Air Pollution: Cancer's Unseen Cause

Air pollution is a mixture of chemicals, particles and other materials in the air that can harm human health. It is a significant and far-reaching threat to public health, with 99% of the world's population breathing unhealthy air, according to the World Health Organization (WHO). Exposure to air pollution has been linked to cancer, stroke, respiratory and cardiovascular diseases, and other health issues.

Outdoor air pollution is caused by emissions from industry, power generation, transportation, and domestic burning, among other sources. Indoor air pollution is caused by radon gas, burning coal or wood, paint or cleaning chemicals, and biological pollutants such as mould or dust mites.

Air pollution has been shown to increase the risk of lung cancer, with outdoor air pollution causing roughly 1 in 10 cases in the UK. While smoking is a much bigger risk factor for lung cancer, air pollution is still a significant concern. Recent studies have also found a link between air pollution and an increased risk of bladder and breast cancer.

The mechanisms by which air pollution can cause cancer are still being studied, but it is believed that air pollutants can generate low-grade and long-term inflammation and oxidative stress, as well as contain mutagens and carcinogens that can damage DNA.

Reducing air pollution is crucial for protecting public health and lowering the risk of cancer.

Outdoor air pollution

Cancer Risk

Mechanisms

There are several ways in which outdoor air pollution may increase the risk of cancer, particularly lung cancer:

• Tiny particles may build up in the lungs and damage DNA in cells, changing how cells divide and leading to cancer.
• Air pollution may cause inflammation in the lungs, which can lead to cancer.
• Air pollution contains mutagens and carcinogens, such as polycyclic aromatic hydrocarbons (PAHs) and dioxins, which can generate DNA adducts and increase cancer risk.
• Air pollution can lead to oxidative stress and an increase in free radicals, which can stimulate cell proliferation, invasiveness, angiogenesis, and metastasis, and inhibit apoptosis, contributing to cancer development.

Interventions

Interventions to reduce outdoor air pollution include:

• Using public transport, cycling, or walking instead of driving private vehicles.
• Reducing emissions from public sector transport services.
• Improving cooking stoves and indoor ventilation, particularly in low- and middle-income countries.
• Advocating for accurate air pollution monitoring and tighter air quality management.
• Increasing green spaces and promoting active transportation, such as walking and cycling.
• Individual-level interventions, such as the use of personal respirators and air filtration systems.

Indoor air pollution

In addition to lung cancer, indoor air pollution has been linked to other types of cancer, respiratory and heart diseases, and other health issues. The risks associated with indoor air pollution are similar to those caused by smoking tobacco. Nearly half of lung cancer cases in people who have never smoked are estimated to be related to air pollution.

To reduce the risk of cancer and other health issues, it is important to minimise exposure to indoor air pollution. This can be done by not smoking indoors, using cleaner energy sources for heating and cooking, and improving indoor ventilation.

Particulate matter

The particles in particulate matter are very small and cannot be seen by the naked eye. However, they can get trapped in the lungs and cause damage to lung cells, leading to inflammation and changes in how these cells replicate. Over time, this can lead to cancer.

According to the World Health Organization (WHO), low- and middle-income countries disproportionately shoulder the burden of outdoor air pollution, especially in Southeast Asia and the Western Pacific regions. Anyone who lives in an area with high levels of particle pollution is at risk of developing lung cancer.

To protect yourself from particulate matter, it is important to reduce your exposure to indoor and outdoor air pollution. Some ways to do this include avoiding second-hand smoke, not burning wood or coal for heating or cooking, and testing your home for radon levels. When spending time outdoors, it is recommended to check the air quality index and limit your activity if pollution levels are high.

Radon gas

Radon is a colourless, odourless, radioactive gas that is produced by the breakdown of naturally occurring radioactive elements such as uranium, found in varying amounts in soil and rock around the world. Radon gas can move from the soil and rock into the air, as well as water sources.

Radon is the second leading cause of lung cancer, after smoking, and is responsible for about 21,000 lung cancer deaths per year. It is the leading cause of lung cancer among non-smokers. Radon gas breaks down into radioactive elements, which can be inhaled and lodge in the lining of the lungs, giving off radiation that damages lung cells.

The risk of radon exposure is higher indoors, in homes, offices, schools and other buildings, particularly in basements. The levels of radon in buildings depend on the characteristics of the rock and soil in the area. Radon can enter buildings through cracks in walls or floors, or gaps in foundations.

The US Environmental Protection Agency (EPA) recommends taking steps to lower radon levels if they reach 4.0 picocuries per litre (pCi/L) or higher. Radon detection kits can be purchased to check radon levels, and mitigation systems can be installed to reduce radon levels.

Radon exposure has been firmly established as a cause of lung cancer over the past four decades, with the highest risk noticed in uranium miners, who work underground and are exposed to high levels of radon.

Benzene and polycyclic aromatic hydrocarbons (PAHs)

Benzene is a colourless, flammable liquid with a sweet odour. It is one of the 20 most widely used chemicals in the United States. It is used to make plastics, resins, lubricants, dyes, detergents, drugs, and pesticides. It is also a natural part of crude oil and gasoline and, therefore, motor vehicle exhaust.

Benzene exposure has been linked with a higher risk of cancer, particularly leukaemia and other cancers of blood cells. It has been shown to induce haematotoxicity in humans and recent studies have reported haematological effects at various benzene levels, including those below 1 part per million in the air.

The International Agency for Research on Cancer (IARC) classifies benzene as "carcinogenic to humans", based on sufficient evidence that it causes acute myeloid leukaemia (AML). The US National Toxicology Program (NTP) and the US Environmental Protection Agency (EPA) have also classified benzene as a known human carcinogen.

The precise mechanisms by which benzene induces tumour initiation remain unknown. However, it is thought that benzene and/or its metabolites cause chromosomal aberrations, such as aneuploidy, commonly observed in AML. Benzene exposure has been associated with higher levels of chromosomal changes, including 5q−/−5 or 7q−/−7, +8 and t(8;21) in the peripheral blood lymphocytes of highly exposed workers.

Several mechanisms have been proposed to explain how benzene induces leukaemia, including:

• The induction of genetic, chromosomal or epigenetic abnormalities and genomic instability in haematopoietic stem cells (HSCs)
• Stromal cell dysregulation
• Apoptosis of HSCs and stromal cells
• Altered proliferation and differentiation of HSCs

Frequently asked questions