Leukemia and farm practices in Iowa.

Death certificate analyses of 1675 white, male Iowans over age 30 years who died of leukemia in 1964-1978 were completed. Each case was matched to two controls on age (within two years) at death, county of usual residence and year of death. Consideration of usual occupation, as recorded on the death certificate, resulted in an odds ratio for leukemia mortality among farmers of 1.24 (p less than 0.05). The highest odds ratios for farmers were observed in those born after 1890, those dying after 1970, and those dying at age 65 years or younger. Odds ratios for farmers were also elevated in counties with high soybean and corn production per acre for those born between 1890 and 1900. For those born after 1900, odds ratios for farmers were increased in counties with the greatest numbers of egg-laying chickens and largest number of acres treated with herbicides. The types of leukemia causing elevated mortalities in Iowa farmers were chronic lymphatic and unspecified lymphatic. Mortality from unspecified lymphatic leukemia was associated with corn per acre, number of milk cows and number of egg-laying chickens.