Chronic obstructive pulmonary disease (COPD) accounts for 3 percent of all disability-adjusted life years lost world-wide according to the 2010 Global Burden of disease report. Approximately 15 percent of cases are linked to occupational exposures such as dust and fumes in the workplace. Auto workers are particularly at risk of COPD when metalworking fluids used during manufacturing become aerosolized, inflaming airways and irritating lungs.
In a new study, researchers at UC Berkeley have found that lowering the recommended occupational exposure limit to aerosolized metalworking fluids may be an effective intervention to save lives. Though the National Institute for Occupational Safety and Health recommends an average daily exposure limit of 0.4 milligrams per cubic meter, the recent analysis found no evidence supporting a threshold below which exposure is safe.
Sally Picciotto, assistant researcher and lead author of the study published in the journal, Epidemiology, examined a longitudinal cohort of over 38,500 auto workers followed for COPD mortality. “We wanted to frame our research question from a direction of health protection. How many years of life could have been saved if we had set the recommended exposure limit at different level?”
“We sometimes struggle to make the results of our studies relevant to policy makers,” says Picciotto. “With this framework, they have a number they can understand and our results are easy to interpret.”
She measured the impacts of lowering the occupational exposure limit for particulate matter less than 3.5 microns in diameter using three types of aerosolized metalworking fluids: straight or oil-based, soluble, and synthetic.
“For each fluid type, we could have saved many years of lost life from COPD had we banned it. For soluble fluids, we could have saved an estimated 1550 years of lost life, and that’s just among the workers who died of COPD.” Straight fluids have gone out of use over time because they’ve been proven to harm health, explains Picciotto. “Solubles were the most commonly used, so more workers would be impacted by a ban of this fluid.”
Lowering the limits for all three fluids would have been less effective than a ban. Picciotto notes banning all three fluids is not realistic, but if the use of respirators were enforced, workers would not be breathing the aerosolized contaminants around them.
“From a methodological perspective,” says Picciotto, “we were also interested in addressing the healthy worker survivor effect. With COPD, because it’s a highly symptomatic and debilitating disease, the people who suffer from it have to leave work permanently and therefore stop accumulating exposure. But others who don’t happen to get sick remain at work longer and may thus accumulate more exposure.” Most statistical analyses would then find that exposure was protective, because the healthier workers were more exposed and the least healthy workers were less exposed.
In studies of COPD, this healthy worker survivor effect can muddy the association between occupational exposure and disease. “This is a very real problem for every occupational study that looks at cumulative exposure.” Their study, therefore, used a statistical method that could avoid this bias.
Co-authors from UC Berkeley include John Balmes, director of COEH, Ellen Eisen, director of the Occupational Epidemiology Program, and Jonathan Chevrier, formerly a research epidemiologist in the School of Public Health and now an assistant professor at McGill University. The study was funded by the Centers for Disease Control – National Institute for Occupational Safety and Health.
Read the paper online at: http://goo.gl/0jz5YP.
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