Occupational hygiene assessment of sheep dipping practices and processes. Final report on HSE project 1/HPD/126/269/92

A collaborative Health and Safety Executive (HSE); Institute of Occupational Medicine (IOM) study of sheep dipping practices was conducted in 1992 using occupational hygiene evaluations of the five most common sheep dipping practices to rank the potential for and extent of operator exposure, the uptake of organophosphate (OP) insecticide, and the working practices contributing to this exposure.Pilot work was undertaken to evaluate and refine a customised visual assessment proforma developed to record working practices as well as the extent and duration of workers’ skin and clothing contact with sheep dip. Airborne concentrations of the OP insecticide diazinon measured during these studies were all less than the analytical detection limit of the method (<0.01mgm-3). The OES is O.lmmgm-3.In the main study sheep dipping with proprietary formulations containing only diazinon were evaluated. Fourteen different sheep dipping operations were studied which involved 38 individuals. The human metabolism and excretion of the active OP ingredient of sheep clip under the conditions observed were assessed. Samples of blood obtained from participating workers were analysed for red cell and plasma cholinesterase activity. Corresponding urine samples were analysed for the metabolites of the organophosphate diazinon; diethyl phosphate (DEP) and diethylthiophosphate (DETP). Photographic records and video recordings were obtained for all visits and were used to assist descriptions of working methods encountered and interpretation of the results.Splashing was caused by a variety of factors mainly related to working practices such as the speed of dipping, the method for sheep entering the bath, the interaction between dipping team members and general operator fatigue during long sessions. The use of appropriate protective clothing was generally poor with personal hygiene and standards of housekeeping variable. Hazard perception was also generally inadequate.Some workers were visibly soaked, particularly paddlers and chuckers, while some helpers were hardly splashed. A number of useful control measures such as splash-guards and remote operation of gates were in use on a number of farms. It was not possible to assess directly exposure caused by contact with contaminated surfaces or concentrated dip although those individuals who handled concentrate had significantly higher concentrations of urinary metabolites.The levels of diazinon metabolites in urine were low, indicating some but relatively little absorption of organophosphate insecticide during the sheep dipping processes. Metabolites of diazinon (DEP + DETP) were detected in the pre-dipping urine samples of 15 out of 36 workers on farms where diazinon was used. This may have resulted from earlier sheep dipping with diazinon. There was little change in the amount of diazinon metabolites detected from pre- to post dipping samples. Sixteen individuals showed no increase; in the remainder increases ranged from 1 to 56 nmol/mmol creatinine. Thirty out of 36 exhibited an increase in metabolites from pre-dipping to next morning; this ranged from 1 to 146 nmol/mmol creatinine. The amount of metabolite present in next morning samples, adjusted for the initial pre-dipping levels, ranged from 0 to 151 nmol/mmol creatinine, the mean being 22.6 and the median 16 nmol/mmol creatinine.When urinary metabolite results were compared with visual occupational hygiene information no association was found between increases in metabolites and particular occupations or dipping bath type. Individual working practice was the overwhelming explanatory factor for increased exposure.The largest decrease observed in plasma cholinesterase activity for any worker was 14%, which was accompanied by a decrease in red cell cholinesterase activity of 2%. This decrease is within the variation which could occur in a normal, unexposed individual. For red cell cholinesterase activity the largest decrease was 10% (experienced by 1 individual) which is the upper limit of intra-individual variation. No worker experienced what would be considered a clinically significant change in either plasma or red cell cholinesterase activity, that is a decrease of more than 30%.Field trials of the HSE's fluorescent imaging technique for assessing skin contamination were performed at six of the participating farms. Contamination was observed but the quantitative estimates may be a little low because of technical problems with the method. The highest observed skin contamination, however, was found on an individual who was observed to be heavily splashed and to have a relatively high urinary metabolite concentration.The study suggests that the most important cause of exposure was from handling concentrated dip with direct splashes from the working strength dip less significant.