Mortality surveys and death certificate studies have suggested an association between
leukemia and farming. To investigate whether exposure to
carcinogens in an agricultural setting is related to risk of
leukemia, the authors conducted a population-based case-control interview study of 578 white men with
leukemia and 1245 controls living in Iowa and Minnesota. Consistent with recent mortality studies, there were slight, but significant, elevations in risk for all
leukemia [odds ratio (OR) 1.2] and
chronic lymphocytic leukemia (OR 1.4) for farmers compared to nonfarmers. There were no significant associations with
leukemia for exposure to specific fungicides,
herbicides (including 2,4-D and 2,4,5-T), or crop
insecticides. However, significantly elevated risks for
leukemia of greater than or equal to 2.0 were seen for exposure to specific animal
insecticides including the
organophosphates crotoxyphos (OR 11.1),
dichlorvos (OR 2.0), and
famphur (OR 2.2) and the
natural product pyrethrins (OR 3.7) and the
chlorinated hydrocarbon methoxychlor (OR 2.2). There were also smaller, but significant, risks associated with exposure to
nicotine (OR 1.6) and
DDT (OR 1.3). This finding of elevated risks for
insecticides used on animals deserves further evaluation.