Epidemiological study of the relationships between exposure to organophosphate pesticides and indices of chronic peripheral neuropathy, and neuropsychological abnormalities in sheep farmers and dippers. Phase 1. Development and valid

A study of sheep dipping practice was conducted in the summer of 1996 in order to develop a model for uptake of organophosphates (OPs) based on simple task, procedural and behavioural aspects of sheep dipping, and to validate the model by comparisons with OP urinary metabolites during various dipping procedures. Occupational hygiene evaluations made by observation of work practices and biological monitoring were used to develop the model. Furthermore, methods for improving the control of exposure to OP dips during dipping operations were identified.This study formed the first part of a three part investigation in to the possible chronic effects associated with OP exposure during sheep dipping. The hypothesis under investigation is that repeated exposures to OP pesticides may cause small increments of damage to nervous tissue, which even allowing for some recovery, may accumulate to the point where it is clinically relevant.The study involved one day surveys of twenty dipping sessions at farms mostly located in the Scottish Borders. Each survey involved observation and recording of the activities performed by individuals including: the frequency and extent of handling the concentrate dip; the extent and time of contact with dip wash (working strength dip); protective clothing worn; hand washing; smoking and eating habits, and any other significant incidents. Sheep dippers were also asked to provide urine samples before and after work. These were used to measure metabolites of diazinon to enable an estimate of uptake to be made. Finally, a brief questionnaire on exposure to sheep dip, other pesticides, and relevant aspects of behaviour during the 72 hours prior to the visit was administered to each individual to allow other possible sources of urinary metabolites to be accounted for.The study found that the most important source of exposure to OPs was contact with concentrate dip, which occurred almost always on the hands and usually as a result handling the concentrate container during the preparation and replenishment of the dipping bath. Levels of urinary metabolites were found to increase with increased handling of the concentrate containers. Larger flock sizes tended to result in more replenishment of the bath and hence more handling of the concentrate. Generally one person at each farm had responsibility for handling concentrate dip, this was usually the paddler, the individual responsible for submerging the sheep in the dip wash. Increased splashing with dip wash was found to be positively associated with increment in urinary metabolites for a subset of individuals who had not been exposed to concentrate dip. Splashing with dip wash was related to proximity to the dipping bath, and was found to be highest for paddlers, then for chuckers, the individual responsible for manoeuvring the sheep into the bath, and lowest for helpers, the individual responsible for herding sheep toward the bath.A comparison was made with the results of two earlier studies undertaken by the IOM (Niven et al, 1993 and Niven et al, 1996) which similarly looked at factors which influenced both exposure and uptake among sheep dippers. These results helped to formulate the structure of the uptake model. The present study confirmed the results of the earlier work particularly in relation to concentrate being the most important source of exposure. The limited observations of exposure to concentrate in earlier studies have been improved upon during this study to allow a quantitative exposure-response relationship to be estimated. A weaker relationship with exposure to dip wash from splashing has also been found in this study as well as in earlier work, confirming that it is also an important source of uptake.Based on the regression analysis of the factors influencing exposure a model has been proposed for the uptake of OPs during a full sheep dipping session:-Uptake = a*CONC + b*DIPThe model requires inputs from the two important sources of exposure identified in the study, CONC representing concentrate and DIP representing dip wash. However, it is acknowledged that other, as yet unconfirmed, sources may have a significant effect on uptake. CONC is the expected number of times concentrate is handled. DIP is the expected time weighted splash score had an individual been observed and data recorded in a manner similar to this study. From the regression analysis which jointly fitted terms for concentrate and dip wash estimates for the coefficients of a and b are 3.6 and 0.2 respectively. This model explains 62% of the variation measured in the present study.Factors which may result in a more acute exposure and which have not been taken account of in the basic splash scores for concentrate and dip wash include paddlers who plunge dip with their hands and incidents of falling into the bath. Data on uptake for these events is minimal or zero in the present study so if they were to be included in the model estimates of the effects on uptake of these events would be required. Alternatively, scores could be derived based on perceived exposure, and the model used to predict the additional effect of this exposure.The refined uptake model has been used to develop a questionnaire for retrospective exposure assessment to be used in the second part of the study. It is essential that the information sought by the questionnaire can be reliably recalled by farmers potentially over the duration of a working life. Therefore, surrogate measures of exposure to concentrate or dip wash have been chosen. The factors chosen relate to important aspects of task or behaviour observed in the present study, and are considered to be relatively constant factors, which farmers could recall in relation to specific jobs, for example the task performed, whether they prepared of replenished the bath and the size of flock.The use of control measures including protective clothing was found to be patchy and fragmented, typical of what is often seen in small businesses. During dipping protective clothing was most commonly worn on the lower body. Gloves were worn by about half of the individuals who handled concentrate, however, none were considered to afford good protection each time the concentrate was handled. An important reason for this was that no individual habitually washed their gloves and as a result concentrate may have permeated the glove material.Eliminating or reducing skin contact with concentrate dip is considered essential to improve the control of exposure. This could best be achieved by improving the design of concentrate containers, the effectiveness of gloves and the working practices of individuals.