M.A. O'Malley, M.L. Verder-Carlos, L. Mehler and D. Richmond
NIOSH Education and Information Division
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.
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NASD Review: 04/2002
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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