Estimation of cumulative exposure to organophosphate sheep dips in a study of chronic neurological health effects among United Kingdom sheep dippers

Abstract

Objectives-To derive a method for retrospectively estimating cumulative exposure to organophosphate (OP) pesticides among a cross section of United Kingdom sheep dippers, as part of a wider epidemiological study of neurological abnormality within this group of workers. Methods-A hygiene study of dipping sessions at 20 farms using diazinon based dips was carried out by two experienced occupational hygienists. Observations on the exposure of people to concentrate and dilute dip were recorded throughout each dipping session, together with the other relevant factors including the use and condition of protective clothing. Concentrations of urinary metabolites of diazinon were used to measure actual exposure to OPs. To estimate exposure in the subsequent epidemiological study, an occupational exposure history questionnaire was developed using results from the hygiene study and an empirical exposure model. Results-In the hygiene study, increased urinary metabolites were associated with the handling of concentrate dip and exposure to dilute dip wash through splashing. Very few dippers wore the recommended protective clothing. The handling of concentrate dip was the principal source of exposure to OPs. Dipping task was used as a surrogate for splashing of dilute dip in retrospective exposure estimation. In the epidemiological study, cumulative exposure to OP sheep dips was highly correlated with the total number of dipping days, but not with age.

Exposure profiles of pesticides among greenhouse workers: implications for epidemiological studies

“…Most studies are limited to the use of surrogate measures of intensity and only few studies have used transparent algorithms to quantify pesticide exposure (Brouwer et al, 1994;Buchanan et al, 2001;Dosemeci et al, 2002). In this study, a task-based model was used, taking into account frequency and duration of different tasks throughout the year, and intensity of pesticide exposure during the tasks.…”

“…Most epidemiological studies on occupational pesticide exposure use qualitative exposure assessment methods that often rely on expert judgment. However, a new generation of studies based on quantitative exposure indices or algorithms is slowly emerging (Brouwer et al, 1994;Buchanan et al, 2001;Dosemeci et al, 2002).…”

The virtues of a deliberately mis-specified disease model in demonstrating a gene-environment interaction

“…In assessing exposure of farmers who dip sheep, repeated measurements from subjects within groups were not collected and, therefore, between- and within-worker variances in the study of Buchanan et al 19 were unknown. However, the magnitudes of between- and within-worker variances were similar across routes of exposure, industries and agents, and were covered by the conditions in the simulation study 23 24…”

“…All subjects were genotyped for specific polymorphisms in the paraoxonase gene. Cumulative exposure for each organophosphate pesticide group was estimated individually according to the procedure previously developed and validated by exposure measurements19 (further details are in Appendix 1). Environmental and working conditions during measurements used to derive the exposure intensity models may have differed from those experiences by cases and referents, creating an additional source of error in estimated cumulative exposure.…”

“…Given that inputs into these calculations were obtained from self-reports, they can be deemed to be imprecise and the resultant cumulative exposure estimates to contain error. Model-based exposure intensity estimation used by Buchanan et al 19 to validate their various exposure metrics, was analogous to group-based assessment of exposure intensity 25…”