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Recent Research – The impact of air pollution on human health

Evidence shows that traffic-related air pollution is a contributory factor to a wide range of diseases

But the most harmful pollutants are currently unregulated

September 22nd 2017

The last few years has seen an increasing amount of research into the impact of traffic-related air pollution on human health. Much of the research has focused on the harmful impact of nitrogen dioxide (NO2) and particulate matter (PM), tiny particles that are emitted by diesel vehicles and other sources. In the UK, nitrogen dioxide emissions have exceeded the legal limit as set by the EU for the last seven years and have been the subject of a long-running legal dispute – see last month’s article ‘Air Pollution in the UK – Seven years of illegal NO2 emissions’. Nitrogen dioxide emissions are known to cause breathing difficulties and have been linked to respiratory symptoms and illnesses such as asthma and bronchitis, while PM particles have been found in the bloodstream, the lungs, and more recently in the brain, with research suggesting links with cardiovascular disease and neurological disorders such as Alzheimer’s disease. [1] In this article, we look at a cross-section of the most significant findings, including research on the impact of air pollution on children, research on the possible links between air pollution and a number of illnesses (such as diabetes, cardiovascular disease, and neurological disorders), and the implications of this research for measures to tackle traffic-related air pollution.

The impact of air pollution on London’s schoolchildren

Two years ago, researchers based at King’s College and Queen Mary College, University of London, published the results of a research project that set out to investigate the effects of air pollution on schoolchildren living within London’s Low Emission Zone. The research was funded by the National Institute for Health Research, NHS health trusts and other bodies. The study focused on 8-9 year-old children from schools located at various distances from a number of air pollution hotspots in the east London boroughs of Hackney and Tower Hamlets. The Low Emission Zone, set up in 2008, was predicted to have a significant effect on PM10 and NO2 concentrations, and the researchers hypothesized that “reduced exposure to traffic emissions would result in a reduction in the prevalence of respiratory/allergic symptoms associated with traffic-related pollutants.” [2]

Data was collected over three consecutive winters, November to March, 2008 to 2011. Respiratory and allergic symptoms were assessed using parent-completed questionnaires. These were collected at each visit, when health assessments were also carried out to examine lung function and collect biological samples. Around 1,800 children at 23 schools were invited to take part in the study, with around a thousand (56%) deciding to participate. Computer modelling techniques were used to gather data on air pollution exposure for the duration of the study (including measurements of NO2 and PM10 levels). Statistical analysis of the data “confirmed the previous association between traffic-related air pollutant exposures and symptoms of current rhinitis,” and also identified a direct correlation between exposure to air pollution and a reduction in lung growth. Speaking to the Sunday Times, Ian Mudway, a respiratory toxicologist at King’s College London, said: “The data shows that traffic pollution stops children’s lungs growing properly. The evidence suggests that by 8-9 years of age, children from the most polluted areas have 5 to 10 per cent less lung capacity and they may never get that back.” [3]

“No evidence that Low Emission Zones can reduce pollution”

Additionally the researchers found that, in contrast to the predicted effect, the Low Emission Zone “did not reduce ambient air pollution levels, or affect the prevalence of respiratory/allergic symptoms over the period studied.” They conclude: “Importantly, the London Low Emission Zone has not significantly improved air quality within the city, or the respiratory health of the resident population in its first three years of operation. This highlights the need for more robust measures to reduce traffic emissions.” [4] Professor Chris Griffiths, who coordinated the research, is a GP and Professor of Primary Care at Queen Mary College, University of London, and the Co-Director of the Asthma UK Centre for Applied Research. He said it was very disappointing that the Low Emission Zone, “which was specifically designed as a major public health intervention, has so far brought about no change. This raises questions over the government’s current consultation on air quality, which is based around the idea of creating similar low emission zones in up to 30 other polluted urban areas. There appears to be no evidence that these low emission zones can reduce pollution or improve health.” [5] In fact, these plans were dropped in the Government’s latest plans to tackle air pollution, as we explained in last month’s article, in favour of the long-term ambition of ending the sale of all new diesel vehicles by 2040, whilst in the shorter-term local authorities will be expected to come up with air quality plans.

The social inequalities of air pollution

The impact of air pollution on London’s schoolchildren was also the subject of a report commissioned by the Greater London Authority which was completed in 2013. Last year, however, the Guardian revealed that Boris Johnson, during his period of office as London’s Mayor, had prevented the full report from being published. [6] Speaking to the Guardian, the report’s author Katie King said that the Greater London Authority had publicly disclosed the positive conclusions in the report – namely, that the number of people exposed to illegal NO2 emissions would fall by 2020 – but had held back the negative findings. “The crux of the report was about understanding the inequalities of air pollution,” she said, “so they chose not to make public the findings regarding inequality. The information that they did take from the report was the positive, that exposure was predicted to fall in the future.” The positive findings were highlighted by the Mayor in a progress report on his air quality strategy, delivered in July 2015. These were the predictions that the number of Londoners exposed to illegal NO2 emissions would drop from 1 million in 2015 to around 300,000 in 2020 as a result of the Mayor’s policies on Low Emission Zones. The Mayor’s progress report also noted that deprived communities were more likely to be exposed to poor air quality, but the Guardian says that “it failed to mention the unpublished report’s revelation that in 2010, 433 of the city’s 1,777 primary schools were in areas where pollution breached the EU limits for NO2. Of those, 83% were considered deprived schools, with more than 40% of pupils on free school meals. Of the remaining schools located in areas below the pollution limit, less than a fifth were in deprived areas.” In response, Boris Johnson denied that there had been any cover-up, saying he had highlighted the problem of primary schools and poor air quality in areas of deprivation. However, the Guardian reports that his office did not deny he had stopped the full report from being released. And given the results of the NHS-funded research, mentioned above, the predictions on the impact of London’s Low Emission Zone may turn out to be unduly optimistic as regards the effects on human health.

The BREATHE project: A study of air pollution and child development

Further evidence of the impact of traffic-related air pollution on child development has come from Spain, where a number of research institutions collaborated on a project called BREATHE (also known as ‘Brain Development and Air Pollution Ultra-fine Particles in Schoolchildren’), which was funded by the European Research Council. [7] The research was based in Barcelona and set out to evaluate the impact of air pollution exposure on cognitive development in primary schoolchildren. The researchers say that air pollution concentrations in Barcelona are among the highest in Europe, partly attributed to high traffic density with a large proportion of diesel-powered vehicles (around 50%), relatively low precipitation, high population density, and an urban landscape characterized by high-storey buildings and narrow streets, which reduces the dispersion of pollutants. Of the 416 schools in Barcelona, 40 schools were selected to obtain the greatest contrast in traffic-related air pollution levels, as measured by NO2 concentrations. Of the 40 schools, 39 accepted the invitation to participate and about 2,700 schoolchildren took part in the project. [8]

Air pollution increases the risk of developing myopia

Data gathered from the BREATHE project and published in April this year showed a link between exposure to traffic-related air pollution and myopia in schoolchildren aged 7 to 10 years of age, as measured by the use of spectacles. In their introduction to the study, the authors state:

“Exposure to traffic-related air pollution is associated with a wide range of adverse health outcomes, with the lungs being one of the most commonly affected organs, mainly because of their constant direct exposure to air pollutants. Similarly, the eyes are directly exposed to air pollution, making them a prime target organ for the adverse effects of such an exposure. In addition to the short-term effects of air pollution on the eye, such as irritation of the ocular surface and its accompanying symptoms and complaints, chronic exposure to air pollution has been associated with long-lasting ocular conditions such as dry eye disease and cataract. Although air pollution could induce myopia through systemic inflammation and oxidative stress, to date no studies have reported on the potential effect of air pollution on the development of myopia.” [9]

In this case, data was collected over a three-year period from 2012 to 2015. Air pollution was calculated by monitoring exposure to NO2 and black carbon particles at school, and by the predictive modelling of exposure to NO2 and PM particles (PM2.5) at home. As a result of their analysis, the researchers conclude that exposure to traffic-related air pollution increases the risk of developing myopia, as indicated by the number of children using spectacles.

Air pollution affects cognitive development

More results from the BREATHE project were published in March 2015. This investigation set out to assess whether exposure to traffic-related air pollution has an impact on children’s cognitive development. [10] As in the previous investigation, around 2,700 schoolchildren aged 7 to 10 years from 39 schools in Barcelona participated. The schools were located in both high and low polluted areas, as measured by traffic-related NO2 concentrations. The children were assessed using computerized tests every three months over four week-long visits in a 12-month period from January 2012 to March 2013. During each visit, air pollution was monitored for levels of NO2, elemental carbon and ultra-fine particles with a dimension of 10–700 nm (i.e. 10 to 700 nanometres), both outside and inside the classroom. Analysis showed that those schools that were closest to major roads had the highest concentrations of pollutants in their classrooms. The children’s cognitive development was assessed through their performance in the tests and an analysis of the long-term changes in working memory and attentiveness. Statistical analyses of the data indicated that children from highly polluted schools had a smaller increase in cognitive development over time compared to children from lowly polluted schools. Children with attention deficit / hyperactivity disorder were even more vulnerable to pollution levels. The researchers conclude: “Importantly, these findings do not prove that traffic-related air pollution causes impairment of cognitive development. Rather, they suggest that the developing brain may be vulnerable to traffic-related air pollution well into middle childhood, a conclusion that has implications for the design of air pollution regulations and for the location of new schools.”

Evidence of slower brain growth in schoolchildren

Further news of these findings was reported in Horizon: the EU Research and Innovation Magazine in July this year. [11] The report mentions some findings that were not reported in the 2015 publication. Anthony King reports the finding that even one high-pollution day before a test could effect a child’s performance. Additionally, he says that the researchers used magnetic resonance imaging (MRI) to examine 350 children, which showed that “high pollution was linked to slower growth in the front of the brain, in an area believed to be important in decision-making, social behaviour and complex thinking.” Professor Jordi Sunyer is a senior researcher at the Barcelona Institute for Global Health and a lead scientist on the BREATHE project. He says that the harmful effects detected in the research are due to ultra-fine PM particles, mainly emitted by diesel vehicles. Ultra-fine PM particles refers to particulate matter that has an aerodynamic diameter smaller than 0.1 micrometres (< 0.1µg/m3 or < 100 nm); these are far smaller than the fine PM particles (PM2.5) which have an aerodynamic diameter smaller than 2.5µg/m3. These ultra-fine particles are tiny particles of carbon that are breathed into the lungs, cross into the bloodstream and travel to the brain, he said: they "stimulate immune cells and produce an inflammatory effect at various levels of the brain." On the implications of the research for the building of new schools, he said: "If you move traffic 50 metres from a school, ultra-fine particle amounts drop by more than half. At 200 metres, you get 10 times less." As well as reducing the number of diesel vehicles in Europe, Professor Sunyer recommends that local authorities take short-term measures to alleviate the problem by creating barriers between air pollution and citizens, including natural barriers such as trees, hedges and 'green walls'.

Links with diabetes

Air pollution may also contribute to the development of diabetes, affecting children in particular. Research published by the American Diabetes Association in 2016 suggests a link between long-term exposure to air pollution (PM10 and NO2) and insulin resistance in the general population, “mainly attributable to pre-diabetic individuals” (i.e. individuals whose blood sugar is abnormally high, a condition that increases the risk of contracting diabetes and cardiovascular disease). [12] The American Diabetes Association has also published evidence which suggests that exposure to elevated concentrations of NO2 and PM2.5 may contribute to the development of type 2 diabetes “through direct effects on insulin sensitivity and β-cell function”. This latter research, published in January this year, studied children aged 8 to 15 years who were classed as overweight or obese and were followed over a three-year period. [13]

Effects on the unborn child?

Research has also investigated the effects of air pollution exposure on children at the foetal stage. A longitudinal study was published two years ago by the American Medical Association in its journal JAMA Psychiatry. [14] The participants included a sample of 40 urban youth who were followed up prospectively from the foetal stage up to the ages of 7 to 9 years. The research in this case focused on the effect of polycyclic aromatic hydrocarbons, described as ubiquitous and toxic environmental pollutants. The researchers detected a “close-response relationship” between exposure to these pollutants and reductions in the white matter of the brain in later childhood. These reductions “were confined almost exclusively to the left hemisphere of the brain and involved almost its entire surface.” The reduced white matter in the left hemisphere was closely associated with a slower speed in processing information during intelligence tests and more severe behavioural problems, including symptoms of attention deficit / hyperactivity disorder. The authors of the study also suggest that postnatal exposure contributes to additional disturbances in the development of white matter in later childhood, a finding that shares similarities with the slower brain growth detected in the BREATHE project, as mentioned above.

Links with cardiovascular disease, strokes and heart failure

There is a growing body of research that has demonstrated a link between particulate air pollution and the development of cardiovascular disease, such as furring of the arteries. [15] For those people already suffering from heart disease, air pollution can worsen their condition. A study published in the British Medical Journal shows that short-term exposure to air pollution increases the risk of a stroke, with a risk of hospitalisation or death from heart failure in the following week, [16] while a study published in the American Heart Association journal Circulation shows that short-term exposure to high levels of air pollution can trigger a heart attack (“myocardial infarction”). [17] The British Heart Foundation (BHF) says air pollution “is a particular problem for the 570,000 people in the UK living with heart failure.” [18] At the British Heart Foundation’s Centre for Cardiovascular Science based at the University of Edinburgh, a team of researchers have analysed data from twelve countries covering more than four million people living with heart failure “and found they had an increased risk of hospitalisation and death where pollution levels were high.” Lead researcher Professor David Newby said: “People with heart failure are a vulnerable group and, when the air quality falls, more of them are admitted to hospital.”

Research at the BHF Centre for Cardiovascular Science

Recent research at the Centre for Cardiovascular Science has been particularly concerned about “nanosized particulate matter in air pollution, such as that derived from vehicle exhaust.” [19] This nanosized particulate matter refers to the ultra-fine particles of air pollution that were featured in the research findings described above. The teams working at the Centre for Cardiovascular Science have published research demonstrating “that acute exposure to diesel exhaust causes vascular dysfunction, thrombosis, and myocardial ischaemia in healthy individuals and in patients with coronary heart disease” (‘myocardial ischaemia’ is a blockage or a hardening of the coronary arteries, resulting in a reduction of the blood flow to the heart muscle). [20] However, while research has demonstrated the links between exposure to particulate air pollution and the development of numerous vascular ailments, the mechanisms through which inhalation could trigger acute cardiovascular events, such as strokes and heart attacks, are only beginning to be understood, and there is a major area of uncertainty surrounding the question of how precisely inhaled particles influence the progression of systemic cardiovascular disease, particularly whether inhaled particles are transported from the lungs, enter the bloodstream and make a direct contribution to cardiovascular disorders.

This was the question that researchers set out to answer in a study that was published by the American Chemical Society in April this year and was carried out by scientists from the UK and the Netherlands. The scientists were based at the BHF Centre for Cardiovascular Science, the Medical Research Council Centre for Inflammation Research (also based at the University of Edinburgh), the University of Edinburgh School of Chemistry, the National Institute for Public Health and the Environment (Netherlands), and Utrecht University and VU University (both in the Netherlands). This particular research was motivated by the growth in engineered nanomaterials and concerns over the potential for human exposure. In their introduction, the scientists say that engineered nanoparticles have “potential similarities to environmental nanoparticles that are associated with significant cardiorespiratory morbidity and mortality.” These environmental nanoparticles are the ultra-fine particles whose dimension is far smaller than the so-called fine particles (PM2.5), as mentioned above. Consequently, the research has implications for our understanding of how precisely air pollution may contribute to the development and progression of cardiovascular disease.

The fate of ultra-fine particles

To find an answer to this question, the researchers recruited 14 volunteers who were exposed to biologically inert, and hence harmless, gold nanoparticles of varying sizes. The volunteers were all male, non-smokers, and aged 18 to 35. Prior to exposure, none of the volunteers had gold detectable in the bloodstream, but gold was detectable in the bloodstream as early as 15mins after exposure in some subjects and was present in the majority at 24 hours. Further research was carried out using 12 volunteers who were suffering from a “cerebrovascular accident,” the medical term for a stroke, and were waiting to undergo surgery. As a result of this research, the scientists were able to conclude that inhaled nanoparticles are transported from the lung into the bloodstream, “where they accumulate at sites of vascular inflammation” (‘vascular inflammation’ is a condition characterised by the build-up of a fatty plaque on the walls of the arteries). The smaller particles were more likely to accumulate, indicating that the ultra-fine particles of air pollution, such as the tiny carbon particles emitted by diesel vehicles, are the most harmful to human health.

News of these findings was reported in the New Scientist in April this year by Michael Le Page, who says that the gold nanoparticles could still be found in blood and urine samples three months after inhalation. [21] Mark Miller, who led the research at the Centre, says that the team was “really surprised that levels were so high three months afterwards.” He described the health implications of the research as follows. When nanoparticles get into the body, he said, they accumulate in the fatty plaques that can grow inside arteries, causing heart attacks and strokes, and the reactive compounds found in air pollution could have all sorts of harmful effects, from impairing the contraction of blood vessels to promoting clotting. The New Scientist also quotes a statement from Frank Kelly, Professor of Environmental Health at King’s College London, who said the study goes a long way towards explaining how air pollution causes vascular injury and disease. “If these findings with gold particles reflect the movement of exhaust-generated carbon particles, then the increased production of very small particles by modern engines is a cause for further concern,” he said.

“Efforts to regulate air pollution are focusing on the wrong particles”

The research also has significant implications for the monitoring of air pollution. The technological devices that are widely used to measure air pollution at the roadside are able to measure the total mass of PM particles in a cubic metre of air, but they are unable to measure the number of such particles. And legal limits for PM emissions, as set by the EU, are based on these measures of total mass. However, thousands of ultra-fine particles can weigh much less in total than a small number of larger-sized particles, and it is the ultra-fine particles that are the most dangerous. This has led Professor David Newby to comment that current efforts to regulate air pollution are focusing on the wrong particles. “We are potentially looking in the wrong place,” he said. And Mark Miller says: “Ideally, we would measure numbers, but the technology is not there.” [22] A further problem is that, while EU legislation sets limits for particulate matter smaller than 2.5µg/m3 (PM2.5), there is no separate regulation for these far smaller ultra-fine particles.

Professor Newby also thinks that the number of ultra-fine particles has risen in the past decade over Europe as a result of diesel emissions, which means that the risk to human health has increased. This is in contrast to those who claim that air pollution has improved over the last few decades because the mass of PM2.5 particles has fallen in most of Europe, as measured by the widely used technology. According to a recent EU assessment of its Ambient Air Quality Directive, PM2.5 levels exceeded the legal limit in just six member states in 2014: the Czech Republic, Poland, Bulgaria, France, Hungary and Italy. [23] And, although the UK has broken the legal limit for NO2 emissions over the last seven years, the EU assessment records that in 2013 the UK was within the legal limit for both PM10 and PM2.5 particles. The EU legal limits that are intended to regulate air pollution mean therefore that the UK Government is under less pressure to tackle the problem of ultra-fine particles. [24]

Legal limits are not safety limits

There is also a further problem here in the disparity between the EU’s definition of legal limits and what the World Health Organization (WHO) regards as safety limits. The WHO guideline values for particulate matter are 20μg/m3 for PM10 and 10μg/m3 for PM2.5, whereas the EU legal limits are 40μg/m3 for PM10 and 25μg/m3 for PM2.5, taken as the average over a twelve-month period. In short, the WHO sets higher standards for safety limits. The WHO published a database in May last year of air pollution statistics from urban areas across the globe. These figures show that the UK breached what the WHO describes as safety limits for PM10 and PM2.5 particles in towns and cities across the UK. Safety limits for PM10 were breached in ten towns and cities. These were: London, Glasgow, Leeds, Nottingham, Southampton, Oxford, Scunthorpe, Port Talbot, Eastbourne, and Stanford-Le-Hope in Essex. Safety limits for PM2.5 were breached in 39 towns and cities. These include the ten already mentioned and Middlesbrough, Carlisle, York, Hull, Manchester, Liverpool, Stoke-on-Trent, Birmingham, Bristol, Newport, Cardiff, Swansea, Plymouth, Portsmouth, Brighton, Southend, and Norwich. If we add to this the problem of measuring and regulating the currently unregulated ultra-fine particles, which scientists now regard as the most harmful to human health, it becomes obvious that current regulatory mechanisms are inadequate to tackle the problem of air pollution. [25]

Pathways to the brain

Returning to recent research, we mentioned above that scientists working on the BREATHE project have said that ultra-fine particles are breathed into the lungs, cross into the bloodstream and travel to the brain, with an MRI scan showing an association between a high level of air pollution and a slower development of a child’s brain. [26] However, other researchers have found that airborne pollutants can enter the brain through an alternative pathway: namely, directly through the nose and the olfactory nerve. Further, the finding that PM particles can enter the brain has led some to suggest there may be a link between air pollution and neurological diseases such as Alzheimer’s disease and Parkinson’s disease.

A significant discovery which made national news was published in September last year in the journal PNAS: Proceedings of the National Academy of Sciences of the USA. [27] The research was carried out by scientists from the UK, Mexico, and the USA, and led by Professor Barbara Maher at the University of Lancaster. The scientists analysed samples of brain tissue from 37 people. Some of the samples came from 29 people who had lived and died in Mexico City and whose ages ranged from 3 to 85. The rest of the samples came from 8 people from Manchester whose ages ranged from 62 to 92 and included some who had suffered from severe to moderate forms of Alzheimer’s disease. The scientists found tiny particles of iron oxide, also known as magnetite, in all of the 37 samples. Small quantities of magnetite can occur naturally in the brain, and in the PNAS paper the authors point out that “biologically formed nanoparticles of the strongly magnetic mineral, magnetite, were first detected in the human brain over twenty years ago.” However, in their research the scientists “used magnetic analyses and electron microscopy to identify the abundant presence in the human brain of magnetite nanoparticles that are consistent with high-temperature formation, suggesting, therefore, an external, not internal, source.” Further, these magnetite nanoparticles matched precisely “the high-temperature magnetite nanospheres, formed by combustion and/or friction-derived heating, which are prolific in urban, airborne particulate matter.”

The authors say that, because many of the airborne magnetite pollution particles are so small, they can enter the brain directly through the olfactory nerves (i.e. the cranial nerves supplying the smell receptors to the nose) and by crossing the damaged olfactory unit. The importance of this discovery is that nano-scale magnetite can respond to external magnetic fields and is toxic to the brain. Nano-scale magnetite is implicated in oxidative cell damage which has a causal link to neurodegenerative illnesses such as Alzheimer’s disease; hence, the authors argue, “exposure to such airborne PM-derived magnetite nanoparticles might need to be examined as a possible hazard to human health.”

Millions of nanoparticles in a single gram of brain tissue

Speaking to BBC News, lead researcher Professor Barbara Maher said she had previously identified magnetite particles in air samples gathered next to a busy road in Lancaster and outside a power station, and she suspected that similar particles might be found in the brain samples. [28] Her suspicions were confirmed by the results which she described as shocking, as a magnetic extraction showed there were a million of these particles in a single gram of brain tissue. It was the shape of the nanoparticles detected in the microscopy that gave a clue as to their origins. Naturally occurring particles of magnetite have a jagged shape, but the majority of the millions of particles found in the tissue samples were smooth and rounded, and displayed features that Professor Maher said could only be created in the high temperatures of a vehicle engine or braking system. “They are spherical shapes and they have little crystallites around their surfaces, and they occur with other metals like platinum which comes from catalytic converters,” she said. These particles were 100 times more numerous than the naturally occurring particles. Professor Maher said it was the first time such particles had been found in the human brain and the discovery opened up a new area of investigation: namely, the question of whether “these magnetite particles are causing or accelerating neurodegenerative disease.”

Links with neurodegenerative disease?

David Allsop is a Professor of Neuroscience at Lancaster University who specialises in neurological diseases and is a co-author of the PNAS paper. Speaking to BBC News, he said that pollution particles could be an important risk factor for conditions such as Alzheimer’s and Parkinson’s disease. “There is no absolutely proven link at the moment but there are lots of suggestive observations,” he said. “Other people have found these pollution particles in the middle of the plaques that accumulate in the brain in Alzheimer’s disease so they could well be a contributor to plaque formation. These particles are made out of iron and iron is very reactive so it’s almost certainly going to do some damage to the brain. It’s involved in producing very reactive molecules called reaction oxygen species which produce oxidative damage and that’s very well defined. We already know oxidative damage contributes to brain damage in Alzheimer’s patients so if you’ve got iron in the brain it’s very likely to do some damage. It can’t be benign.” [29]

However, Dr Clare Walton, Research Communications Manager at the Alzheimer’s Society, said there was no strong evidence that magnetite causes Alzheimer’s disease or makes it worse. “This study offers convincing evidence that magnetite from air pollution can get into the brain,” she said, “but it doesn’t tell us what effect this has on brain health or conditions such as Alzheimer’s disease. The causes of dementia are complex and so far there hasn’t been enough research to say whether living in cities and polluted areas raises the risk of dementia. Further work in this area is important, but until we have more information people should not be unduly worried.” [30]

The search for evidence

In the last twelve months there have been a number of studies that have investigated possible links between air pollution and neurodegenerative illnesses such as Alzheimer’s and Parkinson’s disease . A recent study was published in the journal Environmental Health Perspectives last month. [31] The aim of the research was to examine whether exposure to PM air pollution is related to the risk of contracting Parkinson’s disease. In their introduction, the authors state: “Toxins in air pollution have been shown to promote inflammation and oxidative stress, both of which are thought to contribute to Parkinson’s disease.” The researchers, based at a number of institutions in the USA, followed over 50,000 men in the Health Professionals Follow-up Study, a large cohort of men in the USA which included 550 cases of Parkinson’s disease. They estimated the cumulative average exposure to various sizes of PM up to two years before the onset of Parkinson’s by linking each participant’s place of residence throughout the study with location-specific PM models. Statistical analysis of the results did not show any significant associations between PM exposure and the risk of contracting the disease. They conclude: “In this study we found no evidence that exposure to air pollution is a risk factor for Parkinson’s disease in men.”

Other researchers however have found associations between air pollution exposure and the development of Parkinson’s disease. A review of the available literature on the subject was published in the journal Reviews on Environmental Health in July this year. [32] The review focused on a broad range of studies that investigated possible links between a number of pollutants (including PM particles of various sizes, NO2, and airborne metals) and the development of Parkinson’s disease. The author states: “Air pollution exposure is linked to numerous adverse effects on human health, including brain inflammation and oxidative stress, processes that are believed to contribute to the development and progression of Parkinson’s Disease.” The review produced mixed results: some showed a strong association; some showed a moderate association, and some showed none at all. The author found that the studies that looked at air pollution exposure over a longer time span were more likely to find a positive association. The types of pollutants that were investigated in the studies include PM particles (PM2.5 and PM10), traffic-related NO2 emissions, airborne metals, and second-hand smoking.

The problem of size

In the main, research on the impact of air pollution on human health has tended to focus on the impact of NO2 and PM pollution and, because existing data is more readily available, and because new data can be gathered more easily, on PM2.5 and PM10 particles in particular. There has been far less research on the impact of the smaller ultra-fine particles that have featured in the BREATHE project and the PNAS paper. A nanometre is one billionth of a metre, and the nanoparticles (or ‘nanospheres’) in the PNAS study are less than 200 nanometres in diameter. Writing for BBC News, David Shukman draws a comparison with a human hair, which is at least 50,000 nanometres thick. As the size of the particles decreases, the number of pathways increases, together with the potential to do harm. “While large particles of pollution such as soot can be trapped inside the nose,” he says, “smaller types can enter the lungs and even smaller ones can cross into the bloodstream. But nanoscale particles of magnetite are believed to be small enough to pass from the nose into the olfactory bulb and then via the nervous system into the frontal cortex of the brain.” [33] Airborne particles of a smaller size, such as the ultra-fine particles of carbon emitted by diesel vehicles, would find it just as easy to follow this pathway to the brain. In the search for links between air pollution and neurodegenerative disease, it may be the case therefore, as Professor David Newby suggested above, that researchers have been focusing on the wrong particles.

PM particles classified as carcinogenic by the World Health Organization

The Department for the Environment, Food and Rural Affairs (Defra) says: “Generally, if you are young and in a good state of health, moderate air pollution levels are unlikely to have any serious short-term effects.” However, it continues, elevated levels or long-term exposure to air pollution can affect the respiratory system and “can also lead to more serious conditions such as heart disease and cancer.” [34] The link with cancer was given an authoritative status in October 2013 when the International Agency for Research on Cancer (IARC), an agency of the World Health Organization, issued a press release in which it announced that it had classified outdoor air pollution as carcinogenic to humans (Group 1). [35] This followed a press release issued in June 2012, in which IARC declared diesel engine exhaust to be carcinogenic to humans (Group 1), “based on sufficient evidence that exposure is associated with an increased risk for lung cancer.” [36] The press release on outdoor air pollution, issued in 2013, said:

“After thoroughly reviewing the latest available scientific literature, the world’s leading experts convened by the IARC Monographs Programme concluded that there is sufficient evidence that exposure to outdoor air pollution causes lung cancer (Group 1). They also noted a positive association with an increased risk of bladder cancer. Particulate matter, a major component of outdoor air pollution, was evaluated separately and was also classified as carcinogenic to humans (Group 1). The IARC evaluation showed an increasing risk of lung cancer with increasing levels of exposure to particulate matter and air pollution. Although the composition of air pollution and levels of exposure can vary dramatically between locations, the conclusions of the Working Group apply to all regions of the world.” [37]

What do we know?

The World Health Organization estimated in 2014 that, globally, around 7m premature deaths a year can be attributed to air pollution, while an assessment published in the journal Nature in September 2015 estimates that air pollution contributes to more than 3m premature deaths a year worldwide, “predominantly in Asia.” [38] As regards the UK, a report published in 2016 by the Royal College of Physicians says that each year in the UK, “around 40,000 deaths are attributable to exposure to outdoor air pollution.” [39] And as regards specific outcomes, the World Health Organization has said that evidence published in 2013 “strengthened the causal link between fine particles (PM2.5) and cardiovascular and respiratory ill health. It also showed that long-term exposure to PM2.5 can trigger a range of problems, such as atherosclerosis, adverse birth outcomes and childhood respiratory diseases, and suggested possible links with neurological development, cognitive function and diabetes.” [40]

However, evidence of an association between two phenomena does not mean that one is a cause of the other. Research has shown that traffic-related air pollution can trigger asthma attacks in those suffering from severe forms of asthma, but there is no definitive proof that air pollution is one of the causes of asthma. In the case of diabetes, there is evidence that air pollution increases the risk of contracting the disease in certain individuals, but again there is no scientific evidence of causation. In the case of cardiovascular problems and heart disease, research has shown that air pollution can trigger a stroke and is a significant contributory factor in the development of heart disease, with a growing body of evidence that acute exposure to diesel exhaust does indeed cause a number of cardiovascular problems (see the research at the BHF Centre for Cardiovascular Science, above). But in the case of dementia and other neurological illnesses, the evidence for an association with air pollution is contradictory. What we do know however is that PM particles of different sizes can enter the lungs, the bloodstream and the brain, and have a significant impact on young adults; we don’t know whether this increases the risk of contracting a neurodegenerative disease in later life. The links with respiratory illnesses, lung cancer and cardiovascular disease are more certain. And research has shown that air pollution has a significant impact on children, with consequences for their mental capacity, their physical and cognitive development, and their physical health.

The Call for Action

Four years ago, following the announcement that IARC had classified outdoor air pollution and PM particles as carcinogenic to humans, the World Health Organization said the evidence “reveals the urgent need to take action at the local, regional and global levels to reduce the health threat posed by outdoor air pollution.” [41] It repeated an earlier call to all countries “to develop policies and implement measures to improve air quality to meet WHO guidelines” and “to implement the European Union (EU) legislation on air quality in full, with stricter values for air pollution limits.” The UK Government’s response, as discussed in last month’s article, has been inadequate to say the least, and its actions have been motivated less by the need to take urgent action to reduce a health threat and more by economic concerns, in particular by the need to avoid fines from the EU. Whilst the UK Government’s actions have been ineffective, the World Health Organization said in 2016 that there were signs of hope. The good news was that “awareness is rising and more cities are monitoring their air quality,” according to the WHO’s Director of Public Health, Dr Maria Neira. [42] The research discussed in this article suggests that more needs to be done as regard monitoring, particularly with the methods and the technology used to measure ultra-fine particles, now viewed as the most dangerous for human health. More investment in the research and technology in this area would obviously help. That, together with rectifying the lack of regulation in this area, and resolving the disparity between EU legal limits and WHO safety limits, might create some extra signs of hope.


Photograph: London Borough of Camden Air Monitoring Station © Copyright Mike Quinn and licensed for reuse under this Creative Commons Licence.


[1] The UK Government’s Department for the Environment, Food and Rural Affairs says nitrogen dioxide (NO2) irritates the airways of the lungs, increasing the symptoms of those suffering from lung diseases, while fine particles (PM) can be carried deep into the lungs where they can cause inflammation and a worsening of heart and lung diseases. “People with lung or heart conditions may be more susceptible to the effects of air pollution,” it says. See ‘Effects of air pollution’ at https://uk-air.defra.gov.uk/air-pollution/effects. As well as causing breathing difficulties, high levels of NO2 can trigger asthma attacks for those who suffer from a severe form of the condition. See the Asthma UK website at https://www.asthma.org.uk/advice/triggers/pollution/.
[2] Wood, H., et al. (2015) Effects of Air Pollution and the Introduction of the London Low Emission Zone on the Prevalence of Respiratory and Allergic Symptoms in Schoolchildren in East London: A Sequential Cross-Sectional Study. PLoS ONE 10(8): e0109121. https://doi.org/10.1371/journal.pone.0109121. Retrieved from: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0109121.
[3] Quoted by Laura Donnelly in ‘Air pollution stunting children’s lungs, study finds’, The Telegraph, 25/10/2015. Retrieved from: http://www.telegraph.co.uk/journalists/laura-donnelly/11953613/Air-pollution-stunting-childrens-lungs-study-finds.html.
[4] Ibid: see [2].
[5] Ibid: see [3].
[6] Adam Vaughan and Esther Addley, ‘Boris Johnson “held back” negative findings of air pollution report’, The Guardian, 17/05/2016. Retrieved from: https://www.theguardian.com/environment/2016/may/17/boris-johnson-held-back-negative-findings-of-air-pollution-report. The report’s author Katie King is Director of the environmental consultancy Aether, based in Oxford.
[7] See the BREATHE Project website at http://www.creal.cat/projectebreathe/.
[8] Dadvand, P., et al. (2017) Traffic-related air pollution and spectacles use in schoolchildren. PLoS ONE 12(4): e0167046. https://doi.org/10.1371 /journal.pone.0167046. Retrieved from: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0167046.
[9] Ibid: see [8].
[10] Sunyer, J., et al. (2015) Association between Traffic-Related Air Pollution in Schools and Cognitive Development in Primary School Children: A Prospective Cohort Study. PLoS Med 12(3): e1001792. https://doi.org/10.1371/journal.pmed.1001792. Retrieved from: http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1001792.
[11] Anthony King, ‘Traffic pollution prevents children’s brains from reaching their full potential’, Horizon, 17/07/2017. Retrieved from: https://phys.org/news/2017-07-traffic-pollution-children-brains-full.html.
[12] Wolf, K., et al. (2016) Association Between Long-Term Exposure to Air Pollution and Biomarkers Related to Insulin Resistance, Subclinical Inflammation and Adipokines. Diabetes, 65(8): db151567. https://doi.org/10.2337/db15-1567. Retrieved from: http://diabetes.diabetesjournals.org/content/early/2016/08/16/db15-1567.
[13] Alderete, T., et al. (2017). Longitudinal Associations Between Ambient Air Pollution with Insulin Sensitivity, β-Cell Function, and Adiposity in Los Angeles Latino Children. Diabetes, 66(1): db161416. https://doi.org/10.2337/db16-1416. Retrieved from: http://diabetes.diabetesjournals.org/content/early/2017/01/27/db16-1416.long.
[14] Peterson, B., et al. (2015). Effects of Prenatal Exposure to Air Pollutants (Polycyclic Aromatic Hydrocarbons) on the Development of Brain White Matter, Cognition, and Behavior in Later Childhood. JAMA Psychiatry, 72(6), 531−540. https://doi.org/10.1001/jamapsychiatry.2015.57. Retrieved from: https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2205842.
[15] Brook, R., et al. (2010). Particulate matter air pollution and cardiovascular disease: An update to the scientific statement from the American Heart Association. Circulation, 121, 2331−2378. https://doi.org/10.1161/CIR.0b013e3181dbece1. Retrieved from: http://circ.ahajournals.org/content/121/21/2331.
[16] Shah, A., et al. (2015). Short term exposure to air pollution and stroke: systematic review and metaanalysis. British Medical Journal, 350: h1295. Retrieved from: http://www.bmj.com/content/350/bmj.h1295.
[17] Peters, A., et al. (2001). Increased particulate air pollution and the triggering of myocardial infarction. Circulation, 103, 2810−2815. https://doi.org/10.1161/01.CIR.103.23.2810. Retrieved from: http://circ.ahajournals.org/content/103/23/2810.
[18] ‘Research that shows how air pollution can affect our hearts’, British Heart Foundation. Retrieved from the BHF website at:
[19] Miller, M. et al. (2017). Inhaled Nanoparticles Accumulate at Sites of Vascular Disease. ACS Nano, 11(5), 4542–4552. https://doi.org/10.1021/acsnano.6b08551. Retrieved from: http://pubs.acs.org/doi/abs/10.1021/acsnano.6b08551.
[20] Ibid: see [19]. The relevant research was published in the European Heart Journal and Circulation as follows:
(a) Lucking, A., et al. (2008). Diesel exhaust inhalation increases thrombus formation in man. European Heart Journal, 29, 3043−3051.
(b) Mills, N., et al. (2005). Diesel exhaust inhalation causes vascular dysfunction and impaired endogenous fibrinolysis. Circulation, 112, 3930−3936.
[21] Michael Le Page, ‘Pollution nanoparticles may enter your blood and cause disease’, New Scientist, 26/04/2017. Retrieved from: https://www.newscientist.com/article/2128923-pollution-nanoparticles-may-enter-your-blood-and-cause-disease/.
[22] Ibid: see [21].
[23] Implementation of the Air Quality Directive. A study for the European Parliament’s Committee on Environment, Public Health and Food Safety. Nagl, C., Schneider, J., and Thielen, P. April 2016. Retrieved from: http://www.europarl.europa.eu/RegData/etudes/STUD/2016/578986/IPOL_STU(2016)578986_EN.pdf.
[24] In stark contrast to the EU’s assessment, the authors of the study on London’s Low Emission Zone, published in 2015, state: “Levels of traffic-related air pollution in London are among the worst in Europe, with European Union (EU) limit values for particulate matter with an aerodynamic diameter of < 10μm (PM10) and nitrogen dioxide (NO2) regularly exceeded in many areas of the city" (ibid: see [2]). The Environmental Research Group at King's College London provides real-time data on London's air pollution levels via the London Air Quality Network. The network consist of a number of monitoring stations spanning London and the South-East, funded by local authorities and other bodies, and complemented by modelling techniques that can 'fill in the gaps' to provide the missing data between the stations. For further info, see http://www.londonair.org.uk/LondonAir/General/about.aspx.
[25] The World Health Organization database, including notes on measurements and safety limits, is available as a spreadsheet from the WHO website at: http://www.who.int/phe/health_topics/outdoorair/databases/cities/en/. The full list of the 39 towns and cities in breach of the WHO’s safety limits for PM2.5 in 2016 is: Armagh, Belfast, Londonderry, Prestonpans, Middlesbrough, Carlisle, York, Hull, Manchester, Salford, Warrington, Wigan, Liverpool, Birkenhead, Stoke-on-Trent, Birmingham, Leamington Spa, Bristol, Chepstow, Newport, Cardiff, Swansea, Plymouth, Saltash, Portsmouth, Brighton, Southend, Thurrock, and Norwich. For a summary of the WHO’s findings and reactions to the figures, see: Ian Johnston, ‘Air pollution in UK “wreaking havoc on human health,” WHO warns’, The Independent, 12/05/2016. Retrieved from: http://www.independent.co.uk/environment/dozens-of-british-cities-are-breaching-air-pollution-limits-in-public-health-crisis-a7025401.html. The WHO database was updated in April 2017, with more towns and cities added to the list. For the EU legal limits, see: ‘Air Quality Standards’, European Commission, last updated 22/09/2017. Accessed from: http://ec.europa.eu/environment/air/quality/standards.htm.
[26] Ibid; see [11].
[27] Maher, B., et al. (2016). Magnetite pollution nanoparticles in the human brain. PNAS: Proceedings of the National Academy of Sciences of the USA, 113(39), 10797−10801, 27/09/2016. https://doi.org/10.1073/pnas.1605941113. Retrieved from: http://www.pnas.org/content/113/39/10797.
[28] David Shukman, ‘Pollution particles “get into brain”‘, BBC News, 05/09/2016. Retrieved from: http://www.bbc.co.uk/news/science-environment-37276219.
[29] Ibid: see [28].
[30] Ibid: see [28].
[31] Palacios, N., et al. (2017). Air Pollution and Risk of Parkinson’s Disease in a Large Prospective Study of Men. Environmental Health Perspectives, 125(8): 087011, 18/08/2017. https://doi.org/10.1289/EHP259. Retrieved from: https://ehp.niehs.nih.gov/ehp259/.
[32] Palacios, N. (2017). Air pollution and Parkinson’s disease – evidence and future directions. Reviews on Environmental Health, 21/07/2017. https://doi.org/10.1515/reveh-2017-0009. Retrieved from: https://www.degruyter.com/view/j/reveh.ahead-of-print/reveh-2017-0009/reveh-2017-0009.xml.
[33] Ibid: see [28]. In June this year, the journal Current Environmental Health Reports published a review of the literature on the ways in which air pollutants can find a pathway to the brain. The authors state: “Accumulating research indicates that ambient outdoor air pollution impacts the brain and may affect neurodegenerative diseases, yet the potential underlying mechanisms are poorly understood.” They conclude that, to exert effects on the central nervous system, “multiple direct and indirect pathways in response to air pollution exposure likely interact in concert.” See: Jayaraj, R., et al. (2017). Outdoor Ambient Air Pollution and Neurodegenerative Diseases: the Neuroinflammation Hypothesis, Current Environmental Health Reports, 4(2), 166−179. https://doi.org/10.1007/s40572-017-0142-3. Retrieved from: https://link.springer.com/article/10.1007%2Fs40572-017-0142-3.
[34] Ibid: see [1].
[35] ‘Outdoor air pollution a leading environmental cause of cancer deaths’, IARC Press Release No. 221, 17/10/2013. Retrieved from: http://www.iarc.fr/en/media-centre/iarcnews/pdf/pr221_E.pdf. IARC categories (1, 2a, 2b and 3) are based on an evaluation of the evidence, Group 1 indicating “there is sufficient evidence of carcinogenicity in humans”.
[36]’DIESEL ENGINE EXHAUST CARCINOGENIC’, IARC Press Release No. 213, 12/06/2012. Retrieved from: http://www.iarc.fr/en/media-centre/pr/2012/pdfs/pr213_E.pdf.
[37] Ibid: see [35].
[38] Lelieveld, J., et al. (2015). The contribution of outdoor air pollution sources to premature mortality on a global scale. Nature, 525, 367−371. https://doi.org/10.1038/nature15371. Retrieved from: https://www.nature.com/nature/journal/v525/n7569/full/nature15371.html. For the World Health Organization estimate, see: ‘7 million premature deaths annually linked to air pollution’, WHO News Release, 25/03/2014. Retrieved from: http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/.
[39] Every breath we take: the lifelong impact of air pollution, Royal College of Physicians, February 2016. Available as a PDF from: https://www.rcplondon.ac.uk/projects/outputs/every-breath-we-take-lifelong-impact-air-pollution.
[40] ‘Outdoor air pollution a leading environmental cause of cancer deaths’, World Health Organization News, 17/10/2013. Retrieved from: http://www.euro.who.int/en/health-topics/environment-and-health/air-quality/news/news/2013/10/outdoor-air-pollution-a-leading-environmental-cause-of-cancer-deaths.
[41] Ibid: see [40].
[42] Quoted by Ian Johnston in ‘Air pollution in UK “wreaking havoc on human health,” WHO warns’, The Independent, 12/05/2016. Retrieved from: http://www.independent.co.uk/environment/dozens-of-british-cities-are-breaching-air-pollution-limits-in-public-health-crisis-a7025401.html.


New research will investigate the impact of climate change on the UK’s woodlands

How will increased levels of CO2 affect forest ecosystems?

Birmingham Institute of Forest Research launches carbon enrichment facility to find out

April 19th 2017

Scientists at Birmingham University’s Institute of Forest Research are carrying out a ground-breaking research project that will investigate the impact of climate change on our woodlands. The project will help us to understand how our forests and woodlands will respond to future increases in atmospheric carbon dioxide, including the effects on tree growth and their resilience to agricultural pests and diseases.

The Birmingham Institute of Forest Research (BIFoR) was established some years ago thanks to a £15m. donation from a former professor, and the Institute is supported by the Forestry Commission, Natural England, the Woodland Trust, and a number of other organisations. [1] The project is being carried out in woodlands in Staffordshire and involves “treating 30-metre plots of semi-natural oak woodland to the concentrations of carbon dioxide expected to prevail in 2050. Autonomous sensors and instrumented trees will allow scientists to take measurements continuously and remotely, over timescales ranging from seconds to decades, and to follow the carbon as it is taken up by the plants and moved through the woodland ecosystem.” [2]

The Free-Air Carbon Dioxide Enrichment Facility (FACE)

The apparatus for the field experiment is called a Free-Air Carbon Dioxide Enrichment (FACE) facility and the experiment, the first of its kind in Europe, is one of four similar research projects in other countries with different climates. [3] When combined, BIFoR says this will form the largest machine ever built to study how landscapes will respond to our changing climate. Planning permission for constructing the facility was awarded by Staffordshire County Council in December 2014. Work has been progressing since late spring 2015 on protecting the ecology of the woodland, building the apparatus, and spending a year taking vital baseline measurements before subjecting three of six plots in the woodland to elevated levels of CO2, which started a couple of weeks ago.

BIFoR says that the basic element of the FACE facility is a cylindrical ring structure, supporting pipes that deliver CO2 in such a way that the woodland inside the ring is immersed in elevated CO2 while the rest of the woodland remains largely unaffected. Winds disperse the CO2 continuously so it must be replenished using substantial gas-handling facilities; otherwise, the CO2 would be vented directly to the atmosphere. Six completely open cylindrical rings, 30m wide and as high as the tree canopy, are served by these gas-handling facilities, which store 100 tonnes of liquid CO2 and vaporise and deliver up to 15 tonnes of CO2 per day to 3 of the 6 rings via 25m masts. [4]

“Big Science”

The scientists say that a FACE experiment requires bespoke control engineering which responds rapidly to changes in wind speed and direction “so that CO2 is introduced into the ring always on the upwind side and in just sufficient quantity to maintain the target concentration. A successful experiment will expect to provide CO2 within 10% of the target concentration at least 98% of the time when operating for the entire duration of the CO2 application. In order to detect a signal, and to eliminate effects of the FACE installation itself, control rings must be built in which ambient air is used instead of CO2-enriched air.”

BIFoR describes forest FACE experiments as “big science” and liken the BIFoR programme to a terrestrial ecology version of a space programme, large physics experiments, or advanced manufacturing centres in terms of the requirements for sustained and stringent quality assurance and quality control: “Only in this way, can we ‘follow the carbon’ to establish the true contribution of mature forests to the removal of CO2 from the air.”

The experiment will continue to 2026 at least, and the scientists will be measuring a number of aspects over the next decade, including tree growth and interactions with surrounding ecosystems such as leaf litter, soil and insects. BIFoR’s Director, Professor of Atmospheric Science Rob MacKenzie, said the findings will provide evidence on which to base strategies for the protection of iconic landscape features, such as oak woodlands, into the future.

“The entire experiment depends on changing the woodland as little as possible”

There have been a number of experiments across the globe using FACE facilities, including a project in Australia called AGFACE (the Australian Grains Free Air CO2 Enrichment facility), which “enables the exposure of field-grown crops to elevated CO2 levels under dry-land field conditions.” [5] However, BIFoR chose the woodland at Mill Haft because similar experiments in woodlands have only been carried out on young trees in plantations, whereas Mill Haft Wood is an unmanaged woodland of mature trees. In a paper delivered to the 2016 General Assembly of the European Geosciences Union, the scientists describe the woodland as a “mature oak and hazel coppice-with-standards woodland,” with the oaks estimated to be 150 years old. [6] Reporting on this month’s launch of the experiment, the BBC’s environment correspondent Roger Harrabin says the woodland is part of the former hunting ground of the Earl of Lichfield: “It covers 25 hectares and is thought to have been under continuous tree cover for more than than 300 years.” [7]

In the planning and design stage of the experiment, a major challenge for the scientists was how to build the facility without damaging the delicate natural ecosystem as “the entire experiment depends on changing the woodland as little as possible.” No concrete foundations were used and major elements of the infrastructure were put in place by helicopter. The scientists “nestled all of the experimental equipment into the woodland by hand” while the ancillary buildings were designed to blend in with the woodland. The lighting is low-level and non-intrusive to minimise interference with wildlife and to ensure that the facility sits unobtrusively in its location. The whole site is surrounded by a 3m fence.

On the amount of CO2 that will be used in the course of the experiment, BIFoR says: “Our monthly usage is equivalent to one return transatlantic flight so, although not carbon neutral, our experiment is not as profligate as it sounds and is of course directed at understanding the implications of climate change on our fragile ecosystem.”

Looking after our forests: The need for research

Trees soak up carbon dioxide in the atmosphere via the process known as photosynthesis, releasing oxygen and storing carbon. As humans need oxygen, our relationship with trees is a mutually beneficial one in which trees are fed by CO2 which would otherwise remain in the atmosphere and contribute to global warming, while we are fed by the oxygen. However, estimates of how much of the carbon produced by burning fossil fuels is currently stored by trees varies from 25% to 60%. [8]

As CO2 acts as a plant fertiliser, scientists believe that trees will be able to absorb more CO2 as levels increase, storing carbon in their trunks, roots and organic matter in the soil. On the other hand, however, they also believe that the ability to absorb increased levels of CO2 will be mitigated over time by factors such as rising temperatures, a lack of water and a lack of nutrients, which will counterbalance the fertilizing effect. The question is, how long will trees continue to absorb CO2 as levels increase before these mitigating effects come into play? How will our woodlands respond to future increases in atmospheric CO2, and what will the impact be on tree growth and a plant’s resilience to pests and diseases? [9]

Those are the questions that BIFoR’s research is aiming to answer. Talking to BBC News, BIFoR’s Director Rob MacKenzie said: “The impact of changing CO2 should show up in the leaf chemistry of exposed trees within days, and in the soil within weeks. Within three years stem growth, canopy structure, and a host of other structural forest elements should be different in the patches exposed to elevated CO2. Continuing out to 2026, the ‘push’ provided by the elevated CO2 will pass through all the checks and balances of a mature forest ecosystem, allowing, as each year passes, increasingly better estimates to be made of the extent and capacity of the land carbon sink in 2050 and beyond.” The experiment may also reveal other intriguing effects, he said. For instance, trees in a mature forest, in which the intake and the release of CO2 are in balance, might adapt to high CO2 levels by reducing their pores, which in turn would make them more tolerant to drought.

In the UK, our woodlands face a whole raft of problems specific to the region, such as inadequacies in forestry management and a variety of tree diseases, all of which provide further reasons why this research is vital, as BIFoR explains: [10]

“Forests are critical components of global carbon, nutrient and water cycles, influencing the thermal balance of the planet directly and indirectly, and are home to more than half of all known species. As human populations have expanded, increasing pressures have been placed on forests, with the 20th century witnessing the steepest rise in rates of deforestation. The UK has the lowest woodland cover of any large European country, and what remains is under serious threat from climate change and imported tree diseases such as ash dieback, responsible for the loss of 60-90% of ash trees in Denmark and now identified at 600 sites in the UK. Our forest industries struggle to compete effectively with imports, which now constitute 70-80% of our timber use, and our level of skills in forest management is on the decline just when a leap to sustainable stewardship of our landscape is urgently required. FACE experiments study to what extent these environmental benefits will persist into the future.”


[1] In an article for BBC News, Roger Harrabin said the experimental site in Staffordshire has been funded by a Birmingham alumnus and philanthropist, Professor Joe Bradwell, who made money selling diagnostic medical kits developed at the university, mainly in the USA. BIFoR’s Director Rob Mackenzie said Professor Bradwell calculated that to offset his carbon footprint he needed to plant 300,000 trees, and the research project was part of his commitment. See “Sci-fi forest tracks carbon impact,” BBC News, April 3rd 2017, at http://www.bbc.co.uk/news/science-environment-39472425.

[2] “Unique forest experiment given the green light,” Birmingham University news, 18th December 2014, at http://www.birmingham.ac.uk/news/latest/2014/12/Unique-forest-experiment-given-the-green-light.aspx.

[3] One such research project is focused on an old-growth forest in the Amazon basin near Manaus, Brazil. See “Amazon FACE” at https://amazonface.org/about/.

[4] “The Birmingham Institute of Forest Research (BIFoR),” Birmingham University website at http://www.birmingham.ac.uk/university/building/bifor.aspx and “The BIFoR Vision,” Birmingham University website at http://www.birmingham.ac.uk/research/activity/bifor/about/bifor-vision.aspx#visionimpact.

[5] “AGFACE (Australian Grains Free Air CO2 Enrichment),” Primary Industries Climate Challenges Centre. The researchers say: “To successfully adapt crop production practices and agro-ecosystem management in the face of increasing CO2, plant production must be studied in a range of environments under field conditions… The FACE (Free Air CO2 Enrichment) technique is used internationally at more than 30 sites, investigating a multitude of ecosystems including cropping systems, pastures, and forests.” See http://www.piccc.org.au/research/project/252.

[6] The abstract is available as a PDF from the Copernicus website at http://meetingorganizer.copernicus.org/EGU2016/EGU2016-4919.pdf.

[7] See [1].

[8] “Forests and Climate Change,” Food and Agriculture Organization (FAO) of the United Nations, at http://www.fao.org/docrep/005/ac836e/AC836E03.htm. The FAO says: “The increase of CO2 in the atmosphere has a ‘fertilizing effect’ on photosynthesis and thus plant growth. There are varying estimates of this effect: + 33%, + 25%, and + 60% for trees, and + 14% for pastures and crops.” The figures are taken from Climate Change 2001 – IPCC Third Assessment, published by the IPCC (Intergovernmental Panel on Climate Change).

[9] See our article “Conifers and Climate Change” for news of research on the impact of climate change on conifers. Two research projects have produced results that appear to be contradictory.

[10] “About BIFoR,” Birmingham University website at http://www.birmingham.ac.uk/research/activity/bifor/about/index.aspx.


Photograph: The view towards Mill Haft Wood from the tunnel underneath the Shropshire Union Canal, near Norbury Junction, Staffordshire © Copyright Roger Kidd and licensed for reuse under this Creative Commons Licence. The caption to the photograph says the mile-long embankment supporting the Shropshire Union Canal here was the cause of years of delay to its final opening in 1835: “its height here is about 14m and the distance through the tunnel is about 60m.” Scientists from the Birmingham Institute of Forest Research have created a “living laboratory” at Mill Haft Wood to investigate the impact of increased levels of CO2 on our woodlands.

The State of Nature 2016 – New report examines the causes of wildlife decline in the UK

“The UK is among the most nature-depleted countries in the world,” says the report

56% of the species assessed have declined since 1970, whilst 15% are threatened with extinction

September 21st 2016

A partnership of 53 wildlife organisations published a report last week which gathers together data and expertise from a number of bodies to present “the clearest picture to date” of the status of the UK’s native species. The report, titled The State of Nature 2016, analyses a total of 7,964 species and reveals that 56% of the species assessed have declined since 1970, while 15% (1,199 species) are either extinct or are threatened with extinction in the UK, using internationally recognised Red List assessment criteria.

The partnership covers England, Wales, Scotland, Northern Ireland, the Isle of Man, Jersey and Guernsey and the 53 partners include the RSPB, the Wildfowl & Wetlands Trust, the British Trust for Ornithology, the National Trust, the Woodland Trust, the World Wildlife Fund, the Botanical Society of Britain and Ireland, the Centre for Ecology & Hydrology, the Chartered Institute of Ecology and Environmental Management, Friends of the Earth, and a number of rivers trusts and wildlife trusts as well as several specialist organisations concerned with bats, butterflies, bees, dragonflies, bugs, mammals, badgers, fungi, lichen, plants, amphibians, reptiles, frogs, sharks, whales, dolphins, freshwater habitats and marine ecosystems.

The report builds on a previous State of Nature report published in 2013 which analysed data for the period 2002–2013. The new report includes data for more species and takes a longer view by assessing the period from 1970 to 2013. One of the aims of the report is to examine the causes of wildlife decline and to use the diagnosis to highlight the need for conservation projects across the UK, UK Overseas Territories and Crown Dependencies. A further aim is to demonstrate through the use of case studies how targeted conservation is helping to tackle wildlife decline with projects that have benefited species and habitats. The report’s authors hope that success stories such as these will inspire individuals, organisations and governments to work together to reverse the decline and “bring nature back from the brink.”

“The drivers of change”

On the causes of wildlife decline, the report’s authors reviewed evidence concerning the long-term population trends of 400 terrestrial and freshwater species in the UK, sampled from a variety of taxonomic groups, the three main groups being insects, vascular plants and vertebrates. The authors were then able to quantify the impact, both positive and negative, of a broad range of drivers, spanning the period 1970–2012. Their findings were similar across the three main taxonomic groups included in the study.

They found that the largest driver of change by far is the intensification of agriculture, which has had an overwhelmingly negative impact on wildlife. Farming has changed dramatically over the forty-year period under review, the report says, “with new technologies boosting yields often at the expense of nature.” The transformation of agricultural land through intensive management has seen an abandonment of mixed farming systems; the intensification of grazing regimes; the increased use of pesticides and fertilisers; the loss of marginal habitats, such as ponds, hedgerows and small woodland; and a switch from spring to autumn sowing, reducing food and habitat for many species. According to the report, however, this last practice has also had a positive impact, leading to “the increased winter survival of some species that eat autumn-sown crops” (though milder winters are also a factor here).

The second biggest driver is climate change, but the impact here has been both positive and negative. For instance, more species from southerly climes have extended their range into the UK than those species from northerly climes that have been lost. In addition, milder winters have increased the survival rate of some species. However, the negative factors here include the loss of coastal habitat due to sea level rise; the adverse effect on marine ecosystems due to increases in sea temperatures; and the disruption to a species’ feeding and breeding habits due to changes in seasonal weather patterns, such as winter storms and wetter springs. The authors also warn that “novel interactions between species caused by changes to their distributions are likely to affect them in unpredictable ways.”

There are four drivers of change that have also had a negative impact on wildlife though to a lesser extent. These are, firstly, hydrological change. This is another land management issue, involving the drainage of wetlands, upland bogs, fens and lowland wet grasslands, and also a sustainability issue, involving the over-abstraction of water. Secondly, urbanisation, involving the loss of green space, including parks, allotments and gardens; the loss of wildlife-rich brownfield sites; and the loss of habitats, such as lowland heathland, to development. Thirdly, a decline in woodland management: the cessation of traditional management practices, such as coppicing, says the report, has led to the loss of varied-age structure and open habitats within woodland. And fourthly, a decline in managing other habitats, such as heathland and grassland: the abandonment of traditional management, including grazing, burning and cutting, is crucial for their maintenance, the report states.

A fifth driver of change is forestry, which has had both a negative and a positive impact on wildlife, and again is an issue of land management. An overall increase in the area of forestry plantations, whilst this has increased the habitat for species using coniferous plantations and woodland edges, has also reduced the habitat that plantations replace, particularly lowland heaths and upland habitats.

So what does the report say about positive drivers? The report summarises its analysis by saying, in general, the way habitats are managed has had a greater impact on wildlife than changes in the total amount of habitat. Whilst changes in habitat management have been substantial, changes to the areas occupied by different habitats during the forty-year period have been relatively small, compared to the extent of habitat loss in the past. It is therefore unsurprising that land management features in the positive drivers of change. According to the report, habitat creation and the low-intensity management of agricultural land have had the most beneficial impact on wildlife. Habitat creation, in particular, is classed as a positive driver with no negative impact, and the report cites the examples of the creation of new wetlands, either through conservation work or as a by-product of mineral extraction (see below), and the planting of new broadleaved and mixed woodland.

The low-intensity management of agricultural land involves the introduction of wildlife-friendly farming through programmes such as the Countryside Stewardship scheme. However, this is balanced by the negative consequence of reduced grazing, leading to the loss of some habitats. Increased management of other habitats through conservation management, often by reinstating traditional methods, also has a positive impact, but again is balanced by the negative impact of increased grazing pressure.

The report examines the causes of wildlife decline in more detail by focusing on specific habitats, with sections that deal with farmland; lowland semi-natural grassland and heathland; upland; woodland; coastal habitats; freshwater and wetland habitats; the urban environment, and the marine environment. There are also four separate reports that focus on England, Wales, Scotland and Northern Ireland, whilst a supplement to the main report includes a set of tables with statistical breakdowns for habitats, regions, and taxonomic groups. Taking the UK as a whole, the steepest rate of wildlife decline is found in grassland and heathland (a 60% fall), whilst the marine environment shows the smallest at 38%. Comparing regions of the UK, England fares the worst by far, with a 61% decline in vascular plants, a 62% decline in the butterfly population, and a 49% fall in the bird population.

Helping to halt the decline

The report describes a number of ways to protect the natural environment and of helping wildlife to thrive, including: protecting specific sites via national and international legislation; improving habitats; creating new wildlife sites; creating wildlife corridors between sites; taking action on behalf of particular species; and tackling pressures such as climate change.

However, the drivers of change are not the only source of pressure facing the natural environment. There is also the pressure of funding for conservation projects. The report states that government spending on biodiversity has fallen by 32% in the last eight years as a percentage of GDP. Many environmental charities would struggle to exist without funding from alternative sources, such as donations from the general public, whilst many conservation projects are heavily reliant on volunteers, whose help has been indispensable for their completion. In this context, it is fortunate that companies working in the mineral extraction and aggregate industries have demonstrated a strong commitment to playing a significant role in nature conservation, both financially and physically through specific restoration projects, a fact that is acknowledged in the report.

For instance, the Peak District National Park has formed a partnership with Tarmac which will see the company donate £20,000 a year for the next five years to help the National Park employ a new member of staff. The new member of staff will play a lead role in supporting the Park’s programme of conservation volunteering. Tarmac, which owns a quarry near Buxton, has set a target of delivering 50,000 volunteer hours a year by 2020 and, as part of the partnership with the National Park, its employees will help with projects across the Peak District for one day a month for the duration of the partnership. [1]

As another example, earlier this year the company Banks Mining established a £93,000 endowment fund to support the management of Pegswood Country Park in Northumberland, having completed the second phase of a programme of restoration and landscaping work at the 36.5 hectare site. The park includes the site of a former opencast mine which Banks operated between 1997 and 2005, and the first phase of the work, on land to the east of the former mine, was delivered in 2003 while the surface mine was still operational. The ongoing management of the park has now been handed over to the environmental charity Groundwork, and the landscaping work has included the planting of 575 bushes and trees along the side of a lake, the sowing of nectar-rich grasses, and 1.4km of new public footpaths. [2]

Back to nature: Creating new habitats

The RSPB is also involved in a number of partnerships with mineral extraction and aggregate companies, not only working with them on specific projects but also at a national level. The RSPB leads a nationwide minerals restoration programme in partnership with the Mineral Products Association, the British Aggregates Association, and Natural England. The partnership, called Nature after Minerals, recently launched a new website which provides advice on a range of land management issues, including priority habitat creation; species protection; and strategic minerals planning. The resource enables practitioners to share best practice and showcases case studies that illustrate how restoration projects have benefited biodiversity and have engaged the local community.

Moving on to specific projects, the RSPB recently announced a collaboration with Brett Aggregates and Boskalis, a dredging contractor, which will involve transporting clay, chalk and other construction spoil from tunnelling and building projects to a Brett Aggregates site at Cliffe in Kent, close to the Thames estuary, where it will be used to fill two lakes. Shallows and islands will then be created in the larger of the two lakes, providing an enhanced habitat for wading birds and other wildlife, and complementing the neighbouring 236-hectare RSPB Cliffe Pools nature reserve. A report by Agg-Net says that the Brette Aggregates site at Cliffe is ideally located “as materials from large projects such as the Thames Tideway Tunnel scheme and other commercial developments can be delivered by boat or barge to the wharf-side operation.” Julian Nash from the RSPB said this type of site is rare in the UK and is significant for both the internationally important wetland birds of the south Thames estuary and marshes, and as a nationally important saline habitat. In winter, Cliffe Pools can attract up to 7,000 dunlins, 2,000 lapwings and 3,000 ducks including teal, wigeon, shoveler, mallard, gadwall and pintail, as well as other species including redshank and grey plover plus birds of prey in the scrub and grassland areas, including marsh harriers.

Meanwhile, in Cambridgeshire, the RSPB is at the halfway stage in a 30-year partnership project with Hanson UK which will see the creation of the UK’s largest reed bed from a working sand and gravel quarry. In May, Hanson handed over a further 96 hectares of restored land at its Needingworth Quarry which will double the size of the RSPB Ouse Fen reserve. A report by Agg-Net says the handover will make the reserve bigger than 200 football pitches: “The Hanson-RSPB wetland project at Needingworth is the biggest planned nature conservation restoration scheme in Europe. It began in 2001 and is primarily being created for bitterns, a species that until recently was very rare in Britain. The reserve is also home to other scarce species such as marsh harriers, bearded tits, otters and water voles. Hanson will continue to hand over parcels of land as sand and gravel extraction is completed, eventually forming a 700-hectare reserve and recreating some of the lost wetland habitat that once dominated the Fenland landscape but was lost due to drainage and land-use changes. The reed bed will cover around 1.5 square miles, almost doubling the natural wetland habitat.”

The State of Nature report says that habitat creation is one of the most significant drivers of positive change for the UK’s wildlife and points out that much of this habitat creation has taken place at post-extraction mineral sites, “where old quarries are converted to new wetlands, including reed beds, marshes and open water.” Whilst this is an obvious benefit to wetland species, what about grassland and heathland, the habitat that shows the steepest rate of species decline across the UK?

Some wetland projects do incorporate grassland into the landscaping where this is feasible and desirable, but for a project that deals specifically with grassland we turn to another RSPB partnership, this one with CEMEX. As we reported in a previous news item, the RSPB is working with CEMEX to provide habitats for the twite in Derbyshire and for the turtle dove in Warwickshire. The company is managing hay meadows and creating conditions that will allow plant species more usually associated with arable land to flourish and to provide seeds for the birds to feed on at critical times of the year.

The plight of the turtle dove was highlighted last year when the IUCN added the turtle dove to its Red List list of bird species threatened with extinction. [3] Turtle doves are migratory birds that spend less than half a year in the UK but come here to breed, primarily in the east and south-east of England. Operation Turtle Dove reports that their numbers have fallen by 97% since the 1970s, the main reason being changes in arable farming practice which has had an impact on their habitat and food supply. Farmers and landowners in the east of England have subsequently taken up their cause via the Countryside Stewardship scheme, creating feeding habitat for the birds and allowing their food plants to return to the arable landscape.

Threatened with extinction

The turtle dove was not the only bird to be added to the IUCN Red List of bird species in the UK; the puffin, the Slavonian grebe, and the pochard were also added to the list. The causes of the puffin’s decline are thought to be their vulnerability to pollution and also a decline in their food supply, which has reduced the survival rate of young birds. The decline in Slavonian grebes in the UK is thought to be due to a reduction in successful breeding pairs, whilst the decline in the pochard population is thought to be due to hunting and the destruction of habitat. These additions mean that the Red List of bird species in the UK has doubled from four to eight. [4]

Reacting to the news last October, Martin Harper, the RSPB’s Director of Conservation, said: “Today’s announcement means that the global wave of extinction is now lapping at our shores… The erosion of the UK’s wildlife is staggering and this is reinforced when you talk about puffin and turtle dove now facing the same level of extinction threat as African elephant and lion, and being more endangered than the humpback whale.”

The RSPB said that several themes emerge from an examination of the changes to the UK’s birds in the IUCN Red List, including “a deterioration in the fortunes of some sea birds, such as puffin and razorbill; an ongoing and increasingly intense threat to wading birds, such as godwits, curlew, oyster catcher, knot and lapwing; and an increasing deterioration in the status of marine ducks, such as common eider, which joins the velvet scoter and long-tailed duck as species of concern.”

Returning to the State of Nature report, whilst there are a number of success stories with regard to targeted species, the overall picture remains one of general decline. The song thrush population has halved in the UK since 1970, whilst the hedgehog population has declined by a third in the last twenty years. An index of species status, based on abundance and occupancy data for 2,501 terrestrial and freshwater species in the UK, has fallen by 16% since 1970. In addition, using data for 213 priority species, an index describing the population trends of species of special conservation concern in the UK has fallen by 67% since 1970. The report also cites a new measure that assesses the health of a country’s biodiversity, and this suggests that the UK has lost significantly more nature over the long term than the global average. “The index suggests that we are among the most nature-depleted countries in the world,” says the report.

The report summarises the overall picture thus: “The loss of nature in the UK continues. Although many short-term trends suggest improvement, there was no statistical difference between our long and short-term measures of species’ change, and no change in the proportion of species threatened with extinction.”

The State of Nature 2016 was launched by David Attenborough at the Royal Society in London on September 14th and is available as a PDF download from the RSPB website.


[1] See the article ‘Tarmac backing conservation in Peak District,’ as reported by Agg-Net.

[2] See the article ‘Banks Mining complete Pegswood restoration,’ as reported by Agg-Net.

[3] The IUCN (International Union for Conservation of Nature) use a range of categories to assess the status of a species with regard to its population and the priorities for conservation. These are: 1. Extinct; 2. Extinct in the wild; 3. Critically Endangered; 4. Endangered; 5. Vulnerable; 6. Near Threatened; 7. Least Concern; 8. Data deficient; and 9. Not evaluated. The turtle dove is listed as ‘critically endangered’ in the UK and ‘vulnerable’ globally.

[4] See BBC News for a summary, but note that ‘critically endangered’ in the UK does not necessarily reflect the global status of a species, as in the case of the turtle dove above.


Photograph: Ouse Fen, Phase Seven © Copyright Hugh Venables and licensed for reuse under this Creative Commons Licence. The photograph was taken in 2012 and the caption says that sand and gravel extraction by Hanson has finished in this area, “which will now be re-profiled and covered in a peaty topsoil in preparation for the conversion to a reed bed as part of the RSPB Ouse Fen reserve.” The reed bed will eventually cover around 1.5 square miles, making it the largest reed bed in the UK. For more information, see RSPB Ouse Fen.

Scientists warn of widespread pollution from historic landfills

4,000 old landfill sites are at risk of flooding, some containing hazardous waste

March 9th 2016
Scientists at the British Geological Survey and Queen Mary College, University of London, are warning that the UK faces the risk of pollutants leaking out from the large number of historic landfill sites that pre-date EU waste regulations introduced in the 1990s. It is estimated that there are 21,027 historic landfills in the UK, with 1,264 sites situated in estuaries and coastal areas at risk of erosion, and a further 2,946 sites located on floodplains. Current regulations require landfills to be sealed with a protective lining, thereby insulating the waste from the surrounding land and watercourses. However, older landfill sites, some of which date from the late nineteenth century, are unlikely to have such protection, leaving them at risk of flooding from coastal erosion or severe weather such as heavy rain and storm surges.

A report produced by CIRIA in 2012 [1] says that the number of historic landfills is likely to be an under-estimate owing to a large number of unrecorded illegal sites. In addition, as the 21,000 historic landfills were developed when there were no legal requirements for their management or monitoring, records of the waste that was deposited in them can be incomplete or non-existent. Speaking to The Independent, Dr Daren Gooddy, an environmental chemist at the British Geological Survey, said he was particularly concerned about those historic landfills that are located in areas with a high flood risk and that contain dangerous substances such as hazardous chemicals and asbestos. He calculated that there are 1,655 such sites. “While it’s hard to say for sure, I would suggest that many of these legacy sites are vulnerable to flooding,” he said. “Even when flooding does not occur these sites leach out contaminated waste, which generally gets transported towards the nearest river.”

Dr Kate Spencer, environmental chemist at Queen Mary College, University of London, has been carrying out research to assess the potential impact of flooding and coastal erosion on historic landfill sites on low-lying coastal areas. Her research team is working with the Environment Agency to create a vulnerability ranking which will help to identify those sites that present the greatest danger, based on the risk of flooding and the contents of the landfill. “The work we’ve done in the South-East suggests that there has already been widespread pollution from historic landfills,” she said. “At one site we actually found a blue poison bottle from a pharmacist that had a skull and crossbones on it, with a stopper and liquid inside.”

In a blog post for Friends of the Earth, Guy Shrubsole reports on a visit in 2015 to a leaking landfill at Tilbury on the Thames estuary. Walking along the coast, he discovered that a two kilometre stretch of the Thames foreshore was filled with waste. “But this wasn’t just rubbish deposited by the waters of the Thames as it sweeps through London,” he says. “It was clearly eroding out of the sandy banks next to the shoreline, lapped by high tides. The remains of a former sea wall, derelict and ineffective, could still be seen below the high-water mark. It was providing no defence at all to the hungry estuary, which had chewed away at the land to reveal layers and layers of landfilled refuse.”

Guy Shrubsole says that maps produced by the Environment Agency show there are several historic landfills in the Tilbury area, but tidal defences at such sites are not maintained, leaving them with no protection from tidal surges and rising sea levels. “No one is taking any responsibility for the huge amounts of waste that is now very clearly leaking out of the old Tilbury landfills,” he says. “And this is just one example. If, as the research suggests, there are thousands of old landfills at risk of leaking their wastes into watercourses and the sea across the UK, then this is a massive, ticking time bomb.”

Dr Kate Spencer said that historic landfill sites “date back to a time when there were no protective linings, no regulation about what went in and little in the way of records about the contents. Many are on coastlines highly vulnerable to coastal erosion, storm surges and flooding and the big concern is that they will become even more vulnerable as climate change makes storms more frequent and intense.”

As we reported in a previous news item, scientists from the British Geological Survey have carried out research into river pollution from historic landfill sites. The focus of their investigation was Port Meadow which lies on the banks of the River Thames, north-west of Oxford, where 11 such sites are located. Their research, based on ammonium sampling, concluded that there are potentially thousands of historic landfill sites that are currently leaching large amounts of nitrogen into major rivers, which can damage water quality and trigger nutrient pollution. As climate change makes flooding more likely, leakages from landfills located on floodplains are also likely to increase.

[1] Cooper, N., Bower, G,. Tyson, R., Flikweert, J., Rayner, S., Hallas, A.: Guidance on the Management of Landfill Sites and Land Contamination on Eroding or Low-Lying Coastlines (C718). CIRIA, 2012.

Photograph: Cottenham Landfill, near Chittering, Cambridgeshire © Copyright Hugh Venables and licensed for reuse under this Creative Commons Licence.

Conifers and Climate Change

Europe’s conifers have been warming the planet, say scientists – But other scientists predict a widespread loss of conifers due to climate change

Feb 24th 2016

Two research projects into conifer trees and their relationship to climate change have produced two apparently contradictory results. One research project looked at forest management in Europe since 1750 and concluded that new conifer plantations have created a 0.1°C rise in temperature across the region; in other words, these conifers were contributing to climate change. However, a second research project has predicted a widespread loss of conifer woodlands in South-West USA and in the Northern Hemisphere precisely as a result of climate change.

Research into Europe’s Forests and the Impact of Afforestation

This research was carried out by scientists at the Laboratory of Climate Science and Environment in Gif-sur-Yvette, France, and received coverage on BBC News earlier this month (6th February). The research project set out to investigate the last 250 years of forestry in Europe, looking at historical data, forest management practice, and its potential impact on the climate through the use of computer models and simulations.

Historical data shows that the area covered by Europe’s forests decreased by about 190,000 square kilometres between 1750 and 1850, when woodlands were commonly used to supply fuel and for industrial use such as ship building. [1] The Industrial Revolution saw coal replace wood as the major fuel, and from 1850 to the present day the area covered by Europe’s forests has grown by around 386,000 square kilometres, roughly 10% more land than before 1850. The increase is largely due to afforestation programmes, and an estimated 85% of Europe’s woodlands is now managed by humans. [2]

Trees absorb carbon dioxide from the atmosphere naturally through the process of photosynthesis, and the commonly-held view is that planting more trees will generally mitigate the impact of climate change. However, the common forestry practice, driven by economics, is to plant fast growing, needle-leaved evergreens such as pine and spruce, thought to be more commercially valuable than the slower growing broadleaved trees such as oak. Lead researcher Dr Kim Naudts said this replacement of broadleaved trees with conifers has not had the positive impact one might expect, but rather was making a small contribution to climate change.

She explained: “By changing the forest, we also make changes to the amount of radiation, water, and energy that the forest releases.” Compared to broadleaved trees, conifers are darker and absorb more light, reflecting less solar radiation back into space. They also release less water into the atmosphere through evaporation, and consequently have a lesser cooling effect on the atmosphere. In addition, the management practice of fast growth and fast removal tends to release carbon that would otherwise be stored in forest debris, dead wood and soil. The researchers say this practice means far less carbon is being stored than would have been the case if nature was left to its own devices. Dr Kim Naudts said: “Even well managed forests today store less carbon than their natural counterparts in 1750.” [3]

To measure the impact on climate change, the researchers built computer models that incorporated 250 years of forestry data, including the distribution of tree species and the methods used to harvest wood. Whereas previous models have focused on changes in land types and their impact (such as farmland, forests, heath, and so forth), the model created by Dr Kim Naudts and her team examines how the forests were actually used. A three-dimensional representation of the forest canopy, and its changes in the last 250 years, allows the researchers to see differences in how various tree species interact with the atmosphere. The model also includes the removal of trees for wood products or fuel, and looks at how forestry practice, such as thinning the forest but not removing it entirely, might affect the climate.

The result of these simulations has led the researchers to conclude that the changes in Europe’s forests have created a 0.1°C rise in temperature in the region, with 0.08°C being attributed to the twin factors of solar radiation and evaporation, as explained above, and 0.02°C being attributed to the practice of removing trees for commercial use. The researchers calculate that this rise in temperature equates to 6% of the global warming attributed to the burning of fossil fuels. They say 6% is a significant amount and believe that similar impacts are likely in regions where the same type of afforestation has taken place.

“We shouldn’t put our hopes on forests to mitigate what is an emission problem,” Dr Naudts told BBC News. “Our results indicate that in large parts of Europe, a tree planting programme would offset the emissions but it would not cool the planet, especially not if the afforestation is done with conifers.” The researchers argue that a programme of replacement should be considered. This would mean replacing the conifers as they are harvested with broadleaved species.

The research was published in the journal Science, Vol. 351, Issue 6273, pp. 597-600. DOI: 10.1126/science.aad7270.

News of the research was reported by Patrick Monahan in a Science news release on 5th February. DOI: 10.1126/science.aaf4019.

Research into the Risk of Tree Mortality as a Result of Climate Change

The second research project was carried out by an international team of scientists led by forest ecologist Nate McDowell at the Los Alamos National Laboratory in New Mexico. The scientists set out to investigate the risk of tree mortality as a result of climate change, looking in particular at the impact of drought and rising temperatures on conifers in the pine and juniper woodlands of the South-West USA. In a five-year study, the research team developed and evaluated computational models and simulations which were validated by field experiments, the aim of which was to understand tree mortality at three levels: at the individual plant level; at a regional level; and at a global level.

A news release from the Laboratory explains the impact of drought on a needle-leaf tree as follows: During a prolonged drought, it says, “the very mechanism that a tree uses to preserve its water stores can be its undoing. The tree closes the stomata on its needles to prevent water loss, but this prevents the tree’s food source, CO2, from entering, halting photosynthesis. As the air becomes hotter and drier, subsequent pressure change pulls more water from the roots than can be supplied and the water tension in the plant’s vascular system (xylem) can become so great that the straw-like columns no longer support water flow. The hydraulic system can collapse or the tree undergoes the starvation process, and it subsequently becomes defenceless against bark beetles and disease since it can no longer secrete the thick resin that protects it. As the tree decays after death, the carbon stored in its tissues is released into the atmosphere as carbon dioxide.”

The researchers found that a key predictive element of a tree’s mortality is its ‘pre-dawn water potential.’ A plant’s pre-dawn water potential is a measure of water stress and indicates its water status, resulting in part from soil water availability and atmospheric water demands on the plant’s water use. Experimentally, the team found that dominant evergreens in the South-West died when the tree’s pre-dawn water potential fell to levels that impaired the transport and storage of water and carbon.

The news release explains that the team generated predictions using multiple process-based and empirical models which included data from two of the world’s largest drought studies, both based in New Mexico and developed by Los Alamos National Laboratory. These models were backed up and validated using observations and field experiments. In the field experiments, a large drought plot was installed at one site which manipulates precipitation to test the impacts of drought, and the researchers then monitored a tree’s reaction to these changes. Their field experiments restricted precipitation by 50% to mimic drought conditions, and this resulted in an 80% mortality rate in the mature pines.

The news release continues: “In parallel, the scientists developed cutting edge representations of tree mortality within their models and subsequently evaluated them against the drought-manipulation results as well as against an independent set of data from another site in Los Alamos where pre-dawn water potential was monitored monthly for more than two decades. This resulted in the generation, and subsequent confidence in, state-of-the-art models of forest stress and mortality during drought.” The news release says that the regional models “accurately predicted the pre-dawn water potential of evergreens and 91% of the predictions exceeded mortality thresholds this century due to rising temperatures.”

Moving on from a regional understanding, the scientists compared their regional models with results from global vegetation models to examine independent simulations. They discovered that the global models simulated mortality throughout the Northern Hemisphere that was of similar magnitude, but on a much broader spatial scale, as the evaluated ecosystem models predicted for the South-West USA. The press release says that the conclusion of widespread conifer loss in the Northern Hemisphere is consistent with widespread observations of accelerating forest mortality in North America. Lead researcher Nate McDowell said: “We have been uncertain about how big the risk of tree mortality was, but our ensemble of analyses – including experimental results, mechanistic regional models and more general global models – all show alarming rates of forest loss in coming decades.”

In their conclusion, the authors of the research state that the atmospheric demand for water (known as the vapour pressure deficit) is potentially the largest climate threat to survival because increasing temperatures are driving a chronic increase in evaporative demand despite increases in humidity. The press release says: “In other words, according to Nate McDowell, trees may suffer in many places around the world, even in humid climates, due to global warming.”

The research was published in the journal Nature Climate Change on December 21st 2015. DOI: 10.1038/nclimate2873.

Contradictory Results?

Comparing the conclusions of these two research projects, one might well be baffled by what appear to be contradictory findings: on the one hand, conifers are contributing to climate change; on the other hand, conifers will be wiped out by climate change. The comparison suggests that conifers are pursuing a course of self-destruction, and the driver of the course is the plant’s very structure, together with the biochemical processes that, in other species, ensure a plant’s survival.

However, there are a number of differences in the scope of the research projects, and in their conclusions. The most obvious is that the first project is concerned with the past whilst the second is concerned with the future. The first project looks at the historical record and the impact that forestry practice might have had on the climate. The second project makes use of figures that are predicted for rising temperatures over the next century to make predictions about tree mortality. Given that the impact of climate change (in terms of rising temperature) has been more dramatic in recent decades, what has happened over the last 250 years is not a reliable guide to what may happen in the next 250. In addition, conditions vary from one country to another, and even within smaller regions: in the UK in recent times, for instance, whilst parts of the country were suffering from continued rainfall and flooding, other parts were suffering from drought.

On the research into Europe’s forests, Patrick Monahan highlights the temptation to extend the results to other regions. Writing in Science Magazine, he says: “But Europe’s temperature increase was in large part due to the continent’s specific history of forestry, its location, and the kind of tree species that are present there. The tropics, especially, play by different rules – there, slowing deforestation is almost certain to contribute to cooling, because trees in the tropics release comparatively more water into the atmosphere, seeding clouds that reflect light.” He also quotes a scientist who wasn’t engaged on the Europe forestry project, who points out that their model is only one of many possible models: “If a different model were to use the same parameters, it might find different results.”

On the second project, the authors of the research note that there are uncertainties and assumptions that could make their models underestimate or overestimate potential tree mortality. The predictions are concerned with temperature rise and the impact of drought, but exclude other factors such as wildfire and ‘islands of survival.’ Nate McDowell says: “Resolving these uncertainties is a critical next step for the international community because we need forests now more than ever to absorb carbon dioxide, even as that carbon dioxide and associated warming is threatening their survival. Based on the outcomes of the recent climate talks in Paris, we need to protect our forest to reduce the warming, but we simultaneously need to know how the warming can take out forests.”

If we assume that the management of Europe’s forests does not change, and its conifer plantations add their contribution to a global rise in temperature, then we have the scenario whereby Europe’s conifers could be aiding the demise of their distant relations in South-West USA. Which leads us to conclude with that question on predictability framed by Edward Lorenz in 1979 in an address to the American Association for the Advancement of Science (AAAS): “Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?” [4]


[1] A typical ship built in the 1700s incorporated the wood of 3,000 large oak trees, according to figures in Forests and sea power: The timber problem of the Royal Navy, 1652-1862, Robert G Albion, 1926. Cited in Trade and Dominion, J H Parry, 1971.

[2] “Overall, human activity has removed roughly half of the world’s natural forests, with the greatest losses in densely populated countries. With the exception of Russia, less than 1% of Europe’s ‘old-growth’ forests remain, while some 95% of the continental United States’ forests have been logged since European settlement began.” AAAS Atlas of population & environment, University of California Press, 2000.

[3] Figures from the Carbon Dioxide Information Analysis Center at the Oak Ridge National Laboratory, USA, estimate that a conifer ecosystem complex stores 13 kilos of carbon per square metre, whereas a mid-latitude temperate broad-leaved forest complex stores 9 kilos of carbon per square metre. Cited in AAAS Atlas of population & environment, University of California Press, 2000.

[4] Cited in ‘The Butterfly Effect’, in Chaos – Making a New Science, James Gleick, 1979.


Creative Commons Licence
Forestry Commission site, Mid Wales © Copyright Anthony Bloor and licensed for reuse under a Creative Commons Attribution-ShareAlike 4.0 International License.

New research shows cosmetic products contain large quantities of micro-plastics

“Up to 80 tonnes of micro-plastics could be entering watercourses in the UK every year,” say researchers

Oct 1st 2015

Researchers at Plymouth University have been analysing the quantities of small plastic particles contained in everyday cosmetic and cleaning products such as facial scrubs. The particles – known as micro-beads or micro-plastics – are tiny, measuring a fraction of a millimetre in diameter. Their research has shown that around 100,000 of these micro-plastics could be released into the environment with every application of these types of product.

A press release on the research says that the particles are incorporated as bulking agents and abrasives, and because of their small size it is expected many will not be intercepted by conventional sewage treatment. The researchers estimate this could result in up to 80 tonnes of unnecessary micro-plastic waste entering watercourses every year from the use of these cosmetics in the UK alone, eventually ending up in the oceans and with the potential to cause harm to marine life.

Micro-plastics have been used to replace natural exfoliating materials in cosmetics and have been reported in a variety of products such as hand cleansers, soaps, toothpaste, shaving foam, bubble bath, sunscreen and shampoo. Scientists point to growing evidence that the amount of plastics in marine waters is increasing, with around 700 species of marine organism being reported to encounter marine debris in the natural environment, with plastic debris accounting for over 90% of these encounters.

For the Plymouth University study, the researchers selected brands of facial scrubs which listed plastics among their ingredients, and these were subjected to vacuum filtration to obtain the plastic particles. Subsequent analysis using electron microscopy showed that a 150ml amount of the products could contain between 137,000 and 2.8 million micro-particles.

Lead researcher Imogen Napper said she was shocked to see the quantity of micro-plastics apparent in these everyday cosmetics. “Currently, there are reported to be 80 facial scrubs in the UK market which contain plastic material,” she said. “However, some companies have indicated they will voluntarily phase them out from their products.”

Richard Thompson, Professor of Marine Biology at Plymouth University, said: “Using these products leads to unnecessary contamination of the oceans with millions of micro-plastic particles. There is considerable concern about the accumulation of micro-plastics in the environment. Our previous work has shown micro-plastics can be ingested by fish and shellfish and there is evidence from laboratory studies of adverse effects on marine organisms.”

The research – titled “Characterisation, quantity and sorptive properties of microplastics extracted from cosmetics” – has been published in the Marine Pollution Bulletin.

“Solving business problems with environmental data”

Innovate UK publishes directory of feasibility studies

Sept 29th 2015

Innovate UK, the Government’s innovation agency, has published a directory showcasing the feasibility studies it funded in its 2014 ‘Solving business problems with environmental data’ competition, working in partnership with the Natural Environment Research Council. Innovate UK says that the Government has amassed a large amount of environmental data that could help businesses understand how they might be affected by environmental change and how to manage future risks. Data is routinely collected on subjects such as land cover, precipitation, farm performance, biodiversity, water flows, geological surveys and the marine environment.

The aim of the ‘Solving business problems with environmental data’ competition was to help companies develop innovative products and services that use all the environmental data collected by Government through its various agencies. Projects lasted up to 12 months with a value of up to £200,000. The competition funded 33 feasibility studies with a total of £4 million investment. The directory of the funded projects is available as a PDF from the GOV.UK website.