An epidemiological study of the relations between exposure to organophosphate pesticides and indices of chronic peripheral neuropathy and neuropsychological abnormalities in sheep farmers and dippers

Objectives-To investigate the hypothesis that chronic low level exposure to organophosphates (OPs) in sheep dips is related to clinically detectable m easures of polyneuropathy. Methods-The design was a cross sectional exposure-response study of sheep d ippers and other non-exposed groups. The study group consisted of 612 sheep dipping farmers, 53 farmers with no sheep dipping experience, and 107 cera mics workers. Retrospective exposure information was obtained by questionna ire based on stable and easily identifiable features of sheep dipping found during the first phase of the study; in particular, estimates of handling concentrate and splashing with dilute dip. Neurological assessments were ba sed on a standard neuropathy symptoms questionnaire, and thermal and vibrat ion quantitative sensory tests. Results-Adjusted for confounders there was a weak positive association betw een cumulative exposure to OPs and neurological symptoms, the significance of which was dependent on the inclusion of a few individual workers with ex tremely high exposure. There was no evidence of an association between cumu lative exposure and the thermal or vibration sensory thresholds. However, s eparating the effects of exposure intensity and duration showed a higher pr evalence of symptoms, primarily of a sensory type, among sheep dippers who handled the OP concentrate. There was also evidence that sensory and vibrat ion thresholds were higher among concentrate handlers, the highest exposed group of dippers. Conclusions-The findings showed a strong association between exposure to OP concentrate and neurological symptoms, but a less consistent association w ith sensory thresholds. There was only weak evidence of a chronic effect of low dose cumulative exposure to OPs. It is suggested that long term health effects may occur in at least some sheep dippers exposed to OPs over a wor king life, although the mechanisms are unclear.