We present here a means of evaluating the comparative risk of organophosphate (OP) compounds, employing a standard epidemiologic technique known as a case-control study. The study population consisted of 396 cases of ChE related illness among California agricultural workers and 758 comparison subjects derived from California's Pesticide Illness Surveillance Program (PISP). The cases and comparison subjects differed chiefly in respect to the presence or absence of cholinesterase inhibition (definitely or probably present among the case group and definitely absent among the controls). Approximately 72% of the controls had nonspecific symptoms that could conceivably have been due to exposure to a cholinesterase inhibiting compound but had cholinesterase values within the normal population range. The remaining cases involved respiratory and ocular irritation, and some were demonstrably related to other specific medical diagnoses. The individual compound most frequently associated with exposure to both case and control subjects was mevinphos (158 cases [39.9%] and 337 controls [43.9%]. Other compounds accounting for 10 or more case subjects included the carbamate compound (as a co-exposure) methomyl, oxydemeton-methyl, parathion, phosalone, dimethoate, methamidophos, diazinon, chlorpyrifos, azinphos-methyl, methidathion, and demeton. The exposure factors identified as significant in the crude analysis included application work and field residue exposure. Exposure to multiple category 1 OPs and multiple ChE inhibitors, and several individual compounds proved significant risk factors in stratified analysis. These included phosalone, methomyl, oxydemeton-methyl, and mevinphos. For the application associated ChE-illnesses, exposures to mevinphos (OR=6.2) and multiple ChE-inhibitors (OR=2.9) remained significant in the multivariate analysis. Based on the limitations of the cholinesterase assays without baseline values, some misclassification of illness among control subjects actually related to ChE inhibition was possible. The study was also limited by lack of a population-based control sample. The control group was similar demographically to the California agricultural population as a whole and the number of non-ChE illnesses for each compound showed a significant correlation with the corresponding value for number of reported pesticide applications. This registry based case-comparison provides useful focus on individual organophosphate compounds that deserve increased public health attention.
This research abstract was extracted from a portion of the proceedings of "Agricultural Safety and Health: Detection, Prevention and Intervention," a conference presented by the Ohio State University and the Ohio Department of Health, sponsored by the Centers for Disease Control/National Institute for Occupational Safety and Health.
The authors noted above are from: All at the California Environmental Protection Agency.
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