Diesel fuel emissions associated with cancer – but the risk to the general public is low

The relationship between lung cancer and exposure to diesel exhaust outside of the workplace has not been studied extensively. Measures can be taken to reduce individual and occupational exposure to diesel exhaust. Cancer Council NSW agrees with the conclusion of other reputable cancer organisations, including Cancer Research UK, that diesel exhaust does cause cancer, but the overall risk to the general population is low compared to other risk factors such as tobacco, excess bodyweight, and alcohol.

Emissions from diesel engines are a mix of gaseous compounds and particulate matter. Gaseous compounds include carbon dioxide, water vapour, oxygen, sulphur and nitrogen compounds, carbon monoxide, and low molecular weight hydrocarbons and their derivatives. Particulate matter can contain elemental carbon, organic compounds (including Polycyclic aromatic hydrocarbons, a number of which are known or suspected carcinogens (cancer causing substances)), metals, and other trace compounds. These particles are a public health concern due to their small size (Particulate Matter of ~10 micrometers or less [PM10]) which makes them easy to inhale and able to reach the deep lung.

In June 2012, the International Agency for Research on Cancer (IARC) updated the diesel engine exhaust classification from probably carcinogenic to humans (Group 2A) to carcinogenic to humans (Group 1). IARC is a part of the World Health Organisation which convenes international expert working groups to evaluate the evidence of the carcinogenicity of specific exposures. This category is used when there is sufficient evidence of carcinogenicity in humans. This IARC classification indicates that diesel exhaust damages the DNA, or genetic material, in body cells in a way that leads to cancer, and that this happens in humans. However this classification does not indicate the extent of exposure required to cause this DNA damage, or the significance of the problem for the general population.

The IARC classification of diesel exhaust is based on ‘in vitro’ (studies of cells in laboratory settings), animal and human studies. Studies conducted of cells in laboratory settings such as Petri dishes have shown that diesel exhaust can cause changes in the DNA of those cells. These types of changes are usually necessary for cancer to develop, although not all substances that cause DNA changes also cause cancer.

Animal studies have demonstrated that tumours can develop when diesel exhaust particulate is either applied to the skin or administered internally. A number of studies conducted among laboratory animals such as rats have also shown that long-term inhalation of high concentrations of diesel engine exhaust causes lung cancer in these animals.

Exposure to diesel exhaust is part of everyday life for many Australians. In busy urban areas, exposure to low levels and short-term peak levels of diesel exhaust are often unavoidable. People are exposed to diesel exhaust mainly as a result of inhaling the particles and gases, which then enter the lungs. People may be exposed to diesel exhaust at work, at home, or while travelling; and the amount of diesel exhaust to which individuals may be exposed varies. The main challenges in studying the possible health effects of diesel exhaust among people include: difficulty in defining and measuring the level of exposure, as diesel exhaust is chemically complex and many parts of it are also found in other sources; and difficulty in separating out the impact of other cancer risk factors, such as cigarette smoking.

Lung cancer is the major cancer thought to be linked to diesel exhaust. Most of the recent evidence comes from studies looking at cancer rates among populations that have high levels of exposure to diesel exhaust. Several studies of workers exposed to diesel exhaust have shown small but significant increases in risk of lung cancer. Men with the heaviest and most prolonged exposures, such as railroad workers, heavy equipment operators, miners, and truck drivers, have higher rates of death from lung cancer than men who are not exposed to diesel exhaust fumes as a result of their occupation.

The IARC decision to upgrade diesel exhaust from probably carcinogenic to humans (Group 2A) to carcinogenic to humans (Group 1) followed two papers arising from the Diesel Exhaust in Miners study which were published in the first half of 2012 in the Journal of the National Cancer Institute. This study looked at exposure levels and cancer rates in a population of more than 12,000 miners at eight non-metal mines in the US, and found substantially higher lung cancer rates among those with the highest exposure. The full cohort results showed significant increases in the risk of lung cancer mortality among underground workers as the level of diesel exposure increased, especially among those who had been employed in the mines for more than five years. This nested case-control study, in which miners who died from lung cancer were compared with matched control miners who did not die from lung cancer, showed that, after taking smoking and other lung cancer risk factors into account, miners with heavy exposure to diesel exhaust were three times more likely to die from lung cancer than miners with the lowest exposures.

Reducing your exposure

You can help protect yourself by taking clean transport such as electric trains and light rail whenever possible, and when driving in high traffic areas, closing your car windows and setting the ventilation system to re-circulate the inside air. Additionally, avoid doing regular strenuous exercise in diesel polluted and high traffic areas.

Reducing occupational exposure

Higher exposures to engine exhausts may occur in some occupations, such as transportation and garage work, vehicle maintenance and examination, mining, traffic control and heavy equipment operation. Clear, thoroughly documented workplace practices and training can help reduce diesel exposure. Wherever diesel equipment is operated indoors, the area should be well ventilated. Roof vents, open doors and windows, roof fans, or other mechanical systems can be used to move fresh air through work areas. Respirators should be an interim measure to control exposure to diesel emissions as required.

Diesel equipment operators should use enclosed cabins equipped with high efficiency particulate air filters to reduce exposure to diesel fumes. Routine inspection and regular maintenance of diesel engines is essential to reduce exhaust emissions. The manufacturer’s recommended maintenance schedule and procedures should be strictly followed.

For more information on how to reduce occupational exposure to diesel, please visit the diesel section of kNOw workplace cancer resource developed by Cancer Council.

Advances in technology

In the past two decades, affordable changes in diesel engine technology (e.g., low-sulphur fuel and exhaust after-treatment) have resulted in reductions in diesel particulate matter and the harmful chemical and physical characteristics of diesel exhaust. The Australian Fuel Quality Standards Act 2000 includes requirements of fuel efficiency and the use of emission control technologies. The Fuel Standard (Diesel) Determination Act 2001 sets standards for the physical and chemical properties that must be met before diesel can be supplied for use in Australia.