Air pollution is increasingly recognised as a major contributor to ill health, including cardiovascular disease. One of the most harmful chemicals released by burning fossil fuels – phenanthrene – is linked to heart disease, as well as other illnesses. Here, Professor Holly Shiels outlines work to investigate the sources of air pollution, the effect on cardiovascular health, and how policymakers can act to clean up our air to save our health.

• Of the 12 characteristics of cardiotoxicity, phenanthrene causes 11 of them.
• Burning fossil fuels – including in car engines, and wood burning stoves – is a major source of phenanthrene, with people in urban areas most at risk.
• Building on momentum from recent years, policymakers and public health officials should go regulate emission sources in new buildings, and introduce routine monitoring of phenanthrene and other pollutants.

Globally, poor air quality contributes to more than 4 million premature deaths each year, and is considered one of the biggest issues in global and public health for the next century. Numerous studies have established a strong link between air pollution and cardiovascular disease (CVD), as well as mortality. Exposure to particulate matter (PM) is associated with serious health issues such as cardiac arrhythmias, heart failure, strokes, and heart attacks, with air pollution contributing to nearly 1 in 5 CVD deaths.

One of the harmful components released by burning fossil fuels is polycyclic aromatic hydrocarbons (PAHs), including phenanthrene, a simple structure of three benzene rings. It is often carried on the surface of particulate matter, including very fine particulate matter (PM2.5), so measurements of particulate matter are frequently used as a proxy for phenanthrene exposure. This compound is present in food, water, the gas phase of air pollution, and on the surface of PM2.5. After being released by the combustion of fossil fuels, phenanthrene can break down into even more harmful products, either while still in the environment, or after entering the body.

The relative toxicity of particulates increases as they get smaller, with PM2.5 capable of reaching the smallest areas in the lungs and even entering the blood stream and translocating throughout the body. Humans can breathe in or ingest phenanthrene, and emerging evidence suggests it causes inflammation and oxidative stress which is linked to a range of conditions like gut and bowel diseases.

The impact of air pollution on cardiovascular health

Ongoing studies indicate that chronic exposure to phenanthrene and PAH causes remodelling of heart function, making the heart more susceptible to arrhythmia. This evidence is supported by studies using mouse and sheep models, as well as human tissue cell models.

An evidence review by researchers at The University of Manchester has linked PAHs exposure to higher levels of poor cardiovascular health in urban environments. These substances are cardiotoxic, meaning they disrupt the activity of the heart. Further research from The University of Manchester found that, of the 12 key characteristics of cardiotoxicity, phenanthrene induces 11. Other chemicals that have a similarly damaging effect on the cardiovascular system, such as lead or arsenic, are heavily regulated and monitored, and yet there is no international regulation specific for PAHs like phenanthrene.

People with pre-existing cardiac dysfunction, including those living with obesity, are more affected by air pollution. Older individuals are also more susceptible, potentially due to a stronger inflammatory response – similar to that seen in COVID-19 patients. As such, air pollution plays a role in exacerbating existing health inequalities.

To mitigate these risks, air filters can be effective as phenanthrene tends to stick to them, helping to remove it from the air. Different types of fuels produce different signatures during the refinery process, and the structure of phenanthrene and other PAHs can be modified by methylation, which can make them either less or more toxic.

Policy recommendations

To address the issue of air pollution as a driver of poor cardiovascular health, there are several concrete steps public health policymakers can take.

First and foremost, the Environmental Agency and the Department for Environment, Food and Rural Affairs (Defra) should introduce routine monitoring of phenanthrene and other PAHs, which is not currently undertaken. Instead, PM2.5 is used as a proxy measure, but specific monitoring of PAHs will provide a better understanding of how these compounds travel from emission sources. Identifying hotspots of PAHs will allow for risk-appropriate mitigation strategies, as well as a deeper insight into the relationship between air quality and cardiovascular risk. Researchers at The University of Manchester have used commercially available equipment to develop new, cost-effective methods to measure these substances using columns linked to air pumps.

The Environment Act 2021 set a legal duty for the UK Government to reduce air pollution, including PM2.5, following widespread concerns about the impact of poor air quality on health. Once routine measurement of phenanthrene and other PAHs is established, Defra should update this legislation to include similar targets for reducing these compounds as well.

Secondly, it is advised to introduce air filters in places where vulnerable populations, such as the elderly and those with pre-existing cardiovascular risk factors, are located. Priority should be given to areas near sources of emissions, such as care homes and hospitals near busy roads.

Lastly, wood burners, which are significant sources of PM2.5 in urban areas, should be regulated more strictly. Although regulations introduced in 2022 required new burners and fuel sources to meet new standards, local authorities have been slow to enforce these regulations, with just four fines issued in 2023 – 2024. Environmental health and health protection teams should prioritise tackling air pollution, and the Ministry for Housing, Communities and Local Government should mandate that no new-build houses in urban areas be fitted with wood-burning stoves.

The Government has recognised air pollution as the largest environmental risk to public health in the UK, directly contributing to between 28,000 and 36,000 deaths every year, at a cost to the NHS and social care of more than £40 million each year. Taking more decisive action on poor quality would help to ease pressures on health services, both directly through pressure on primary care, and in reducing one of the key underlying drivers of persistent ill-health and inequalities. Given the potent cardiotoxicity of phenanthrene, and PAHs more broadly, policymakers and public health officials should make effective steps to reduce exposure a key priority.