12 June 2012
The International Agency for Research on Cancer (IARC), which is part of the World Health Organization (WHO), today classified diesel engine exhaust as carcinogenic to humans (IARC Group 1). After a week-long meeting, the group of international experts agreed that there was “sufficient evidence” that diesel exhaust exposure is associated with an increased risk for lung cancer.
In 1988, IARC classified diesel exhaust as probably carcinogenic to humans (Group 2A). An IARC Advisory Group which reviews and recommends future priorities had recommended diesel exhaust as a high priority for re-evaluation since 1998.
The cancer-causing potential of diesel exhaust has been indicated by a number of studies, particularly those that examined workers exposed to diesel exhaust, as occupational exposure levels tend to be significantly higher than exposures in environmental settings. The IARC decision has been apparently prompted by the recently published results of the Diesel Exhaust in Miners Study (DEMS)—a large US National Cancer Institute/National Institute for Occupational Safety and Health study of occupational exposure to diesel emissions in underground miners, which showed an increased risk of death from lung cancer in exposed workers. The study monitored over 12,000 miners with diesel exposure from the time when the mine company first introduced diesel equipment (between 1947 and 1967) until the end of the study in 1997.
The scientific evidence was reviewed by the IARC Working Group who found that diesel exhaust is a cause of lung cancer (sufficient evidence) and also noted a positive association (limited evidence) with an increased risk of bladder cancer (Group 1). The Working Group also concluded that gasoline exhaust was possibly carcinogenic to humans (Group 2B), a finding unchanged from the previous evaluation in 1989.
While the epidemiological and toxicological research reviewed by the Working Group found a link between cancer and certain components of diesel exhaust—in the particulate and/or gas phase—the IARC has not identified which diesel emissions may cause cancer and classified the entire “diesel exhaust” as carcinogenic. This weakens the value of the IARC assessment as a guidance for governments and other decision makers in their development of environmental standards. After all, diesel exhaust is not a well-defined substance. It consists primarily of nitrogen, oxygen and water vapor, with the actual pollutant emissions that are responsible for health effects being highly variable among different engine technologies.
Perhaps due to this vague definition of the carcinogenic agent, the IARC assessment (based itself on research with old technology diesel engines) was unable to perceive health benefits from modern diesel engines, fueled with ultra-low sulfur diesel and equipped with emission aftertreatment such as particulate filters. Commenting on the evolution of diesel engine technology, the IARC press release said that “while the amount of particulates and chemicals are reduced with these changes, it is not yet clear how the quantitative and qualitative changes may translate into altered health effects; research into this question is needed.” Indeed, what can be reduced is the amount of pollutant emissions coming out of the tailpipe, such as PM and NOx emissions—the amount of “diesel exhaust” from a diesel engine will always remain unchanged.
During the Q&A period at a media event held after the announcement, a question was asked about modern engine technology in view of the results of the ACES study—referenced by the Diesel Technology Forum in their statement on the IARC decision. The ACES study found few health effects from US 2007 heavy-duty engines. Dr Christopher Portier, Chairman of the IARC Working Group, could not provide any comments on the question.
The IARC assessment carries more value for countries where diesel emissions remain unregulated. Dr Christopher Wild, Director, IARC, said that “today’s conclusion sends a strong signal that public health action is warranted. This emphasis is needed globally, including among the more vulnerable populations in developing countries where new technology and protective measures may otherwise take many years to be adopted.”
The summary of the evaluation will appear in The Lancet Oncology as an online publication ahead of print on June 15, 2012.