By Mark S. Kuhar
A study of more than 12,000 nonmetal miners in the United States has determined that heavy exposure to diesel exhaust increases risk of death from lung cancer. The study was carried out by researchers from the National Cancer Institute (NCI), part of the National Institutes of Health, and the National Institute for Occupational Safety and Health (NIOSH), part of the Centers for Disease Control and Prevention, both parts of HHS. The results were distributed in two papers on March 2, 2012, from the Journal of the National Cancer Institute.
The study came under an intense battle starting in 1996 between government researches and the Methane Awareness Research Group (MARG) Diesel Coalition who fought for years to prevent publication of the research that evaluated cancer risk from diesel exhaust, particularly as it may relate to lung cancer, among 12,315 workers at eight non-metal mining facilities. The facilities were located in Missouri (1 limestone mine), New Mexico (3 potash mines), Ohio (1 salt mine), and Wyoming (3 trona mines, which process an ore used in soda ash).
The investigators selected underground mines for their study setting because the heavy equipment used in these mines frequently runs on diesel fuel. In the fairly enclosed environments of these mines, exhaust builds up in the air to levels considerably higher than those found in other occupational settings – like trucking depots or shipyards – and many times higher than the air inhaled by the general population. The investigators selected only non-metal mines because of their characteristically low levels of other exposures that may be related to lung cancer risk, such as radon, silica and asbestos.
The diesel research took into consideration lung cancer risk factors, including smoking, employment in other high-risk jobs, and history of other respiratory diseases.
To quantify exposure for each worker, the investigators collected thousands of measurements of constituents of diesel exhaust in the air at each mine and combined those data with historical exposure information. Importantly, diesel exhaust levels were quantified by measurements and estimates of one of its key components, respirable elemental carbon, which is considered the best index of diesel exhaust in underground mining. The same exposure measurements were used in both the cohort and case-control analyses. The methods for this effort were published previously in four papers in the Annals of Occupational Hygiene in 2010. A fifth paper – an evaluation of the exposure assessment – was published March 2012 in the same journal.
In a news release on the study, Debra Silverman, Sc.D., chief of the Occupational and Environmental Epidemiology Branch in the Division of Cancer Epidemiology and Genetics (DCEG) at the National Cancer Institute, said, “It was vitally important to undertake a large study of diesel exhaust and lung cancer based on a quantitative assessment of historical exposure, taking into account smoking and other potentially relevant factors in order to estimate lung cancer risk,” said lead author of the case-control study.
The risk of lung cancer among heavily exposed underground workers was five times the risk observed among workers in the lowest exposure category.
“These data are especially revealing as they show the effect of diesel exhaust in the absence of smoking,” said Silverman. Although based on small numbers, non-smokers with the highest level of diesel exposure were seven times more likely to die from lung cancer than non-smokers in the lowest exposure category, according to the study.