Update of the morbidity experience of employees potentially exposed to chlorpyrifos

Chlorpyrifos, an organophosphate ingredient of several important insecticides, has been manufactured at The Dow Chemical Company for 25 years. A previous morbidity study among employees of The Dow Chemical Company found no increased prevalence of illness or symptoms among employees potentially exposed to chlorpyrifos from 1977 to 1985 compared with matched controls. The purpose of the current study was to update the original study to 1994, thereby increasing the statistical power.

In the present study, 496 potentially exposed subjects were identified and matched for age, race, sex, pay, and year of hire to 911 control subjects. Morbidity data were abstracted from company medical records.

The prevalence of peripheral neuropathy was not significantly increased among this group of employees potentially exposed to chlorpyrifos. Significantly increased prevalence odds ratios were identified for five diagnostic categories: diseases of the ear and mastoid process; acute respiratory infections; other diseases of the respiratory system; general symptoms, signs, and ill defined conditions; and symptoms, signs, and ill defined conditions involving the digestive system. There was a strong association of diagnosis with duration of observation period, indicating that the exposed workers were more likely than unexposed workers to have a diagnosis abstracted from the company medical records due to their longer mean period of follow up. Analyses by exposure classification and mean plasma cholinesterase activity did not show a dose response.

These data do not support a cause and effect relation of the diagnoses mentioned and exposure to chlorpyrifos.