The February 2020 edition of Air Pollution News, the newsletter published by the All Party Parliamentary Group on Air Pollution, published an article by Dr Robin Russell-Jones.
APPG Newsletter February 2020
Air Pollution is a global problem. 90% of the urban population worldwide are exposed to levels above the WHO guideline limit for small particulates (PM2.5) of 10 microgrammes per cubic metre of air (µg/m3).  Recent studies estimate that air pollution causes 8.8 million premature deaths globally, which represents 15.7% of all deaths.  This makes ambient air pollution the greatest preventable cause of death globally, bigger even than smoking at 7.2 million deaths.
The new estimate for mortality in the UK is 64,000 premature deaths annually. UK citizens lose on average 2.2 years of life due to a health hazard that is beyond their control. These latest estimates are based on 41 studies from 16 different countries. 
Excess mortality is only a small part of the total picture. A joint Royal Colleges report from 2016, based on 40,000 deaths annually, estimated that air pollution in the UK costs the economy £20 billion per annum, with mortality contributing only 8% of the total. The rest relates to morbidity – in other words the chronic effects of air pollution which begin before birth, and persist throughout life. This review will examine some of these other effects.
“Air Pollution costs the economy £20 billion per annum, with mortality contributing only 8% of the total.”
Birth-weight is a critical measure. An analysis of 32 studies linking pregnancy outcomes with the level of small particulates (PM2.5) concluded that each increase of 10 µg/m3 in PM2.5 lowers birth-weight by 16 grams. It is well known that smoking during pregnancy also lowers birth weight, but mothers have the option of stopping, and most do. Living in urban areas does not give pregnant women this option. In Central London pregnant women are exposed to a level of small particulates that will lower the birth weight of their baby by around 24 grams. It is the equivalent of passive smoking twenty four hours a day for 9 months.
Levels of PM2.5 in the capital are below the annual EU limit of 25 µg/m3, but the health effects of small particulates are without threshold. The EU commission are currently reviewing the Ambient Air Quality Directive and are likely to lower the annual limit. In the US, the legal limit is 12 µg/m3, and 8 µg/m3 in Australia.
During the Olympic Games in 2008, the Chinese Government made every effort to reduce pollution levels in Beijing, notably by restricting vehicle access, and birth weight increased. The maximum benefit (23 grams) was for women who were in the last trimester of their pregnancy during the Olympic Games – in other words the stage of pregnancy associated with maximum foetal growth.
Exposure in utero
Low birth weight is linked to a host of adverse outcomes in later life, including lower IQ. Evidence also exists for a direct impact of pollution during pregnancy. Polycyclic Aromatic Hydrocarbons (PAHs) are generated by any combustion process, so members of the public are exposed from activities such as smoking, cooking, domestic fires, and of course traffic, particularly diesel. Researchers in New York have reported that exposure to PAHs during pregnancy in non-smoking mothers is linked to developmental delay at 3 years; an IQ reduction of 4-5 points at 5 years; increased anxiety, depression and inattention at 6-7 years; reduced surface white matter in the brain at 8 years; and delayed self-regulatory behaviour that was most significant at 11 years.
These observations have not yet been replicated in the UK. Even so the situation may be worse as diesel vehicles represent a much larger proportion of the UK car market than in the US. Since 2000 the proportion of new vehicles which run on diesel has increased from 14% of the new car market to almost 50%. Levels of Benzo-a-pyrene, the only PAH monitored in the EU, have increased by 52% at traffic monitoring sites since 2000.
Effect on IQ
These observations have profound implications for public health and educational attainment. UK children and teenagers are currently suffering a mini epidemic of mental health problems which the medical profession are struggling to explain. Commentators have targeted social media, but the toxic impact of air pollution on developing brains is equally worthy of attention, and a vital area for further research.
Thus air pollution has also been linked with IQ deficits in teenagers and a recent London based study showed higher rates of depression amongst teenagers exposed to higher levels of air pollution.14,15 It could be argued that these associations are not causal, but intervention studies are compelling and cannot be dismissed so easily. For instance, a recent US study demonstrated an increase in the cognitive performance of school children when air filters were fitted to schools in Los Angeles.
There are also data showing that air pollution also impacts cognitive function in later life. A systematic review in 2016 identified 31 studies linking air pollution with cognitive decline: 15 in the Americas, 5 in Asia and 11 in Europe. In 2017 a study of 2.2 million older adults living in Ontario showed that their chances of developing dementia increased the closer they lived to a major highway, indicating a dose-response relationship for traffic-derived pollution and dementia. In 2018 a study of 75 GP practices in Greater London showed that the chances of developing dementia was linked to ambient levels of both PM2.5 and NO2. The authors concluded that 14% of dementia cases in the UK are attributable to air pollution.
It is obvious that the UK Government should be doing more to mitigate these health effects.
HMG could increase the tax on diesel, introduce a diesel scrappage scheme, bring forward the phase-out date for fossil fuel vehicles from 2035 to 2030, and give councils the powers to identify and fine highly polluting vehicles at the roadside. They should also introduce WHO limits by 2030 at the latest with a mandatory air quality standard for PM2.5 of 10 µg/m3, and an intermediate target of 12 µg/m3 by 2025.
Instead, DEFRA has produced a Clean Air Strategy which conspicuously fails to address the problem posed by diesel. It contains a commitment to halve the number of people in the UK exposed to levels above the WHO limit for PM2.5 by 2025. This is not a standard. This is an aspiration that lacks any legal force
It is for these reasons that the UK needs a Clean Air Bill and a National Clean Air Agency tasked with responsibility for both indoor and outdoor air quality.
Dr Robin Russell-Jones is Scientific Advisor to the APPG on Air Pollution. He was previously Chair of CLEAR, The Campaign for Lead Free Air.
- Landrigan P et al. ‘The Lancet Commission on pollution and health.’ Lancet (2018); 391: 464-512
- Lelieveld et al. ‘Cardiovascular disease burden from ambient air pollution in Europe reassessed using novel hazard ratio functions.’ European Heart Journal, (May 2019); vol.40: 1590-96: https://doi.org/10.1093/eurheartj/ehz135
- Burnett R et al. ‘Global estimates of mortality associated with long-term exposure to outdoor fine particulate matter.’ Proceedings of the National Academy of Sciences of the USA (2018); 115: 9592-9597 15
- Royal College of Physicians and the Royal College of Paediatrics and Child Health ,‘Every Breath We Take: The Lifelong Impact of Air Pollution’ (2016): https://www.rcplondon.ac.uk/projects/outputs/every-breath-we-take-lifelong-impactair-pollution
- Sun X et al. ‘The association between birth weight and exposure to fine particulate matter (PM2.5) and its chemical constituents during pregnancy: a meta-analysis.’ Environ pollution (2015); 211: 38-47. https://doi.org/10.1016/j.envpol.2015.12.022
- Smith R et al. ‘Impact of London’s road traffic air and noise pollution on birth weight: retrospective population based cohort study.’ BMJ (2017);359:j5299
- Rich D et al. ‘Differences in birth weight associated with the 2008 Beijing Olympics air pollution reduction: results from a natural experiment.‘ Environ Health Perspect (2015);123: 880-87
- Perera F et al. ‘Effect of prenatal exposure to airborne polycyclic aromatic hydrocarbons on neurodevelopment in the first 3 years of life among inner-city children.’ Environ Health Perspect (2006); 114: 1287-1293’
- Perera F et al. ‘Prenatal airborne polycyclic aromatic hydrocarbon exposure and child IQ at age 5 years.’ Pediatrics (2009); 124: 195-202
- Perera F et al. Prenatal polycyclic aromatic hydrocarbon (PAH) exposure and child behaviour at age 6-7 years. Environ Health Perspect (2012); 120: 921-926.
- Peterson B et al. ‘Effects of prenatal exposure to air pollutants (Polycyclic Aromatic Hydrocarbons) on the development of brain white matter, cognition, and behaviour in later childhood. ‘ JAMA Psychiatry (2015); 72: 531-40.
- Margolis A et al. ‘Longitudinal effects of prenatal exposure to air pollutants on self-regulatory capacities and social competence.‘ Journal of Child Psychology and Psychiatry (2016); 57: 851-60.
- European Environment Agency 2016 report. EEA report no 28/2016: https://www.eea.europa.eu/publications/airquality-in-europe-2016
- Wang P et al. ‘Socioeconomic disparities and sexual dimorphism in neurotoxic effects of ambient fine particles on youth IQ: A longitudinal analysis.’ PLOS ONE (2017); 12(12): e0188731. https://doi.org/10.1371/journal.pone.0188731
- Roberts S et al. ‘Exploration of NO2 and PM2.5 air pollution and mental health problems using high-resolution data in London-based children from a UK longitudinal cohort study.’ Psychiatric Research 2019; 272: 8-17.
- Gilraine M et al. ‘Air Filters, Pollution and Student Achievement.‘ EdWorking Paper No 20-188. (Jan 2020)
- Clifford A et al. Exposure to air pollution and cognitive functioning across the life course- A systematic literature review. Environ Research (2016); 147: 383-398.
- Chen H et al. ‘Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: a population-based cohort study.’ The Lancet (2017); 389:718-726.
- Carey I et al. ‘Are noise and air pollution related to the incidence of dementia? A cohort study in London England.’ BMJ Open (2018);8:e022404.doi:10.1136/bmjopen-2018-022404
- Russell-Jones R. ‘Air pollution in the UK: better ways to solve the problem.’ BMJ (2017); 357:j2713 doi: 10.1136? bmj.j2713.
- DEFRA. Clean Air Strategy Published Jan 14. 2019. Ref PB14554. GOV.UK : https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/770715/clean-air-strategy-2019.pdf