Academic journal article Environmental Health Perspectives

Use of Dieselized Farm Equipment and Incident Lung Cancer: Findings from the Agricultural Health Study Cohort

Academic journal article Environmental Health Perspectives

Use of Dieselized Farm Equipment and Incident Lung Cancer: Findings from the Agricultural Health Study Cohort

Article excerpt


Diesel exhaust has recently been classified by the International Agency for Research on Cancer as a lung carcinogen based primarily on epidemiological findings in miners and truck drivers and bioassays (Benbrahim-Tallaa et al. 2012). However, other occupational groups have exposure to diesel exhaust (Pronk et al. 2009). For example, farmers and agricultural workers have used diesel-powered equipment, such as tractors, combines, large trucks, and other heavy equipment since at least the 1970s in the United States (Coble et al. 2002; U.S. Census of Agriculture 2015).

Despite their potential exposure to diesel exhaust, it has been observed in multiple studies, including the Agricultural Health Study (AHS), that farmers have lower rates of lung cancer than the general population (Blair et al. 1992; Koutros et al. 2010). This may be explained partially by a lower prevalence of smoking (Blair and Freeman 2009). However, it may also be attributable to endotoxins, a component of the outer membrane of Gram-negative bacteria present in organic dust, which have been linked to reduced risk of lung cancer, likely through immunologic mechanisms (Lundin and Checkoway 2009). High levels of endotoxins have been reported in agricultural settings, particularly in animal farming and during machine harvest (Liebers et al. 2006). A few epidemiologic studies, including the AHS, have shown reduced risks of lung cancer associated with contact with farm animals (dairy farming, poultry, and large numbers of livestock) after adjustment for smoking (Beane Freeman et al. 2012; Mastrangelo et al. 2005).

We evaluated whether the use of dieselized farm equipment was associated with total and subtypes of lung cancer in farmers and their spouses in the AHS, while considering smoking and concomitant potential exposure to endotoxins.


Cohort enrollment and follow-up. The AHS is a prospective cohort study that includes licensed pesticide applicators (private and commercial applicators) and their spouses in Iowa and North Carolina (Alavanja et al. 1996). Because we were interested in farm-related exposures, we restricted the present analysis to private applicators (i.e., farmers) and their spouses. Farmers were recruited between December 1993 and December 1997 from pesticide certification sessions (84% of eligible farmers enrolled) and completed a self-administered questionnaire during the session. They were given a second, more detailed questionnaire on other occupational exposures to complete at home and return by mail (take-home questionnaire). This questionnaire was completed by 22,916 farmers (44% of 52,394 enrolled farmers) at enrollment. Farmers who returned the take-home questionnaire were similar to nonresponders with regard to demographic characteristics, farming practices, and medical history (Tarone et al. 1997). Spouses of the 43,692 enrolled farmers who reported their marital status as married or living as married were asked to complete a questionnaire, brought home by the farmers, which was different from the farmer take-home questionnaire. A total of 32,345 spouses returned the questionnaire, which we estimated to be 74% of the eligible population.

Cohort members are matched to cancer registry files in Iowa ( and North Carolina ( for case identification and to the state death registries (Iowa:; North Carolina: and the National Death Index to ascertain vital status ( We identified incident cancers between date of enrollment and 31 December 2010 for North Carolina and 31 December 2011 for Iowa. Histological subtype was coded according to the International Classification of Diseases for Oncology, 2nd and 3rd Revision. We identified cohort members no longer residing in Iowa or North Carolina by linkage to several national databases, including Internal Revenue Service records and address databases, and pesticide license registries of the state agricultural departments. …

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