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Diesel Exhaust in Miners Study links lung cancer to diesel exposure

8 March 2012

A study of non-metal miners in the United States found that heavy exposure to diesel exhaust increased the risk of lung cancer and the risk of death from lung cancer. The study was carried out by researchers from the National Cancer Institute (NCI) and the National Institute for Occupational Safety and Health (NIOSH).

The research—a part of the “Diesel Exhaust in Miners Study”—was designed to evaluate cancer risk from diesel exhaust, particularly as it may relate to lung cancer, among 12,315 workers at eight non-metal mining facilities that used diesel equipment. The facilities were located in Missouri (1 limestone mine), New Mexico (3 potash mines), Ohio (1 salt mine), and Wyoming (3 trona mines). Data was collected on the miners’ health and exposure levels to various air pollutants from the time when the mine company first introduced diesel equipment—between 1947 and 1967—until the end of the study in 1997. Only non-metal mines were selected because of their characteristically low levels of other exposures that may be related to lung cancer risk, such as radon, silica, and asbestos. The study used elemental carbon as a marker for exposure to diesel exhaust.

The results of the study were reported in two complementary papers. The first documented the risk of dying from any cause, with an emphasis on lung cancer, using data from the full study population (the cohort study). The second reported on the lung cancer deaths in the cohort study (the case-control study). Results of the case-control study were controlled for other known lung cancer risk factors, including smoking, employment in other high-risk jobs, and history of other respiratory diseases.

The cohort study found that the risk of lung cancer among heavily exposed underground workers was five times the risk observed among workers in the lowest exposure category.

The results of the case-control study, which took into account smoking and other lung cancer risk factors, showed a three-fold risk of lung cancer death overall and about a five-fold risk for heavily exposed underground workers, which was consistent with the cohort analysis. “Heavily exposed” workers were defined as those with elemental carbon exposures above 1005 μg/m3 (the median of the top quartile).

The study—finished in 1997—was conducted at the time when “Tier 0” diesel engine technology of high exhaust emissions was used in mines and miner’s exposure to diesel particulate matter was not regulated. Since May 2008, a miner’s exposure to diesel PM in an underground non-metal mine must not exceed 160 μg/m3 (8 hour average), defined as total carbon (the sum of elemental carbon and organic carbon).

The Diesel Exhaust in Miners Study has been a subject of a controversy and a legal dispute since the mid-1990. In the most recent chapter, in August 2011, a US District Court in Louisiana affirmed an earlier ruling granting a mining industry coalition led by the Mining Awareness Resource Group the right to a review of any data before publication. This decision was stayed by a US Court of Appeals on February 29, 2012, which opened the door for the publication. The papers with the study results were published online on March 5, 2012 in the Journal of the National Cancer Institute.

Source: NCI