OBJECTIVES: To investigate the hypothesis that chronic low level exposure to 
organophosphates (OPs) in sheep dips is related to clinically detectable 
measures of polyneuropathy.
METHODS: The design was a cross sectional exposure-response study of sheep 
dippers and other non-exposed groups. The study group consisted of 612 sheep 
dipping farmers, 53 farmers with no sheep dipping experience, and 107 ceramics 
workers. Retrospective exposure information was obtained by questionnaire 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 based on a standard 
neuropathy symptoms questionnaire, and thermal and vibration quantitative 
sensory tests.
RESULTS: Adjusted for confounders there was a weak positive association between 
cumulative exposure to OPs and neurological symptoms, the significance of which 
was dependent on the inclusion of a few individual workers with extremely high 
exposure. There was no evidence of an association between cumulative exposure 
and the thermal or vibration sensory thresholds. However, separating the effects 
of exposure intensity and duration showed a higher prevalence of symptoms, 
primarily of a sensory type, among sheep dippers who handled the OP concentrate. 
There was also evidence that sensory and vibration 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 with 
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 working life, 
although the mechanisms are unclear.