Occupational hygiene assessment of exposure to insecticides and the effectiveness of protective clothing during sheep dipping operations

A study of sheep dipping was conducted in 1992 and 1993 to assess the adequacy of guidelines for protective clothing and working methods to protect sheep dipping operators against skin exposure to sheep dips containing organophosphates (OPs). Occupational hygiene evaluations, biological monitoring and biological effect monitoring were used to establish the effectiveness of recommended protective clothing and the body uptake of OP when sheep dips were used according to manufacturers’ guidelines.The main study was undertaken at twelve farms during two phases. In the first phase surveys lasted two days on each farm. Contamination and penetration of protective clothing with OP (propetamphos or diazinon) was assessed using garment samplers. These absorbent suits were worn outside protective clothing on one day and inside on another. Absorbent gauze patches were attached to the outer layer of clothing on both days to obtain an estimate of differences in external contamination between the two days. At the end of each dipping session garment samples were sectioned into 6 pieces, and stabilised where necessary before removal to the laboratory, with the patch samples, for analysis.Penetration of insecticide through the protective clothing was generally minimal with protection factors ranging between approximately 4 and > 1000. The maximum amount on an entire internal sampling suit was approximately 6 mg, although 90% were less than 1 mg of insecticide compared with up to approximately 100 mg when the sampling suit was worn outside the protective clothing. Most of this penetration was detected on the lower arms and legs. A positive association was observed between total patch insecticide masses and the amount found on the corresponding sampling suits. The relationship was less clear when individual suit areas were compared with their associated patches. To assist with evaluation of contamination and comparison of the survey days factual information, such as number and rate of sheep dipped, length of dipping session, amount of concentrated dip used, the method of replenishing the dip bath and the size and composition of the dipping team was recorded. A semi-quantitative assessment of observed splashes on each member of the team was also made using a simple scoring system during every dipping session. At almost every farm, on both days, individuals who plunged the sheep under the dipping liquid (paddlers) had the highest splashing score and, where present, helpers had the lowest score (those gathering sheep). These findings were similar to those obtained from the external garment samplers.During the second phase of the study 32 individuals provided two samples of blood (pre- and post-dipping) and three urine specimens (pre-, post-dipping and next morning) for cholinesterase activity determination and urinary metabolite analysis respectively. Half the farms studied used dips based on the OP diazinon while the remaining six farms used chlorfenvinphos-based dips.Concentrations of metabolites of diazinon (diethyl phosphate (DEP) and diethyl thiophosphate (DETP)) ranged from less than the detection limit (approximately 1 n mole/m mole creatinine) up to 227 n moles/m mole creatinine. Increases in urinary concentrations of over 20 n moles/m mole creatinine were observed in only four individuals. Urinary concentrations only increased by up to 20 n moles/m mole creatinine for all other workers and the urinary metabolite concentrations actually dropped for two individuals. Concentrations of dimethyl derivatives (which are not metabolites of diazinon) were found in at least one urine sample from all participants and in some increased during the sampling period. The reasons for this are not clear.The pattern for urinary concentrations of dichlorobenzoic acid, a product of the metabolites of chlorfenvinphos, was similar to that of diazinon. No urinary metabolites of chlorfenvinphos were detected in the urine of 10 of the 15 workers studied, even after dipping. The highest observed concentration was 47 n moles/m mole creatinine, with other concentrations ranging from 20 to 35 n moles/m mole creatinine.No subject experienced a clinically significant fall in plasma (> 15%) or erythrocyte (> 10%) cholinesterase activity. The highest recorded fall in plasma cholinesterase activity was 9% which was not accompanied by change in erythrocyte cholinesterase activity.A weak positive association was found between splashing score and the increase in urinary metabolite concentration. This relationship was, however, overwhelmed by events at, at least, one farm.The study concludes that supervised use of protective clothing ensembles recommended by NOAH in 1992 resulted in minimal contamination underneath the garments. The guidelines, if followed correctly, effectively reduced the potential exposure and can be regarded, however, as adequate.Concentrations of urinary metabolites in urine were low indicating some but relatively little absorption of OP insecticide during the sheep dipping process. The range of results was similar to that found in another study where no special protective clothing was worn.