Diesel exhaust particles are highly respirable with mutagenic and carcinogenic compounds adsorbed on their surface. Based on results from laboratory studies in rats and limited evidence in humans, the International Agency for Research on Cancer classified diesel exhaust as a probable human carcinogen in 1989. However, the interpretation of past epidemiologic studies has been limited due to lack of direct measures of diesel exposure and insufficient years of follow-up. We have identified a unique national cohort of 55,750 long-term trucking company workers employed in 1985. We propose to conduct an extensive exposure assessment and assess the association of exposure to diesel exhaust with lung cancer mortality through 2000. The US trucking fleet has included diesel vehicles since the early 1950s. Therefore, there are trucking company workers with long duration of exposure and at least 20 years since first exposure. We will use the results from the exposure assessment, along with external databases of pollution and truck registrations, to develop a prediction model for diesel exhaust exposure and form categorical groupings of exposure levels. The model will include factors that are readily available in company personnel records such as job title and terminal characteristics so that exposure levels can be linked to the individual employees. We will assess ever-exposure, cumulative and duration of exposure. We will use the results from a questionnaire mailed to all current workers to control for potential confounding by smoking. In this retrospective follow-up, we will have 80 percent power to detect a relative risk of 1.25. This large cohort provides a unique opportunity to detect (or refute) suggested carcinogenic effects of diesel exhaust based on animal toxicology and limited epidemiologic studies. Furthermore, since the range of exposure in these workers includes levels similar to the general population, the findings will be relevant to understanding general population risk of lung cancer from diesel emissions and other fine particulate air pollution.
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