Patch technique, pesticide exposure

The feasibility of employing fluorescent tracers and video imaging analysis to quantify dermal exposure to pesticide applicators has been demonstrated under realistic field conditions. Six workers loaded a tracer with the organophosphate pesticide, diazinon, into air blast sprayers, and conducted normal dormant spraying in pear orchards. They were examined prior to and immediately after the application. UV-A illumination produced fluorescence on the skin surface, and the pattern of exposure was digitized with a video imaging system. Quantifiable levels of tracer were detected beneath cotton coveralls on five workers. The distribution of exposure over the body surface varied widely due to differences in protective clothing use, work practices and environmental conditions. This assessment method produced exposure values at variance with those calculated by the traditional patch technique. 

The personal samples on the chest and back allow an estimate of pesticide exposure based on the standard technique of extrapolating from patch to total body region. The standard method only considers unprotected regions of the body to be exposed. In this case, only the head and neck of the workers are unprotected, and in four of six cases face shields were worn. Thus, beyond a comparison of head and neck exposure for workers 1 and 2, it is not clear how the patch technique could be applied in this study. Later in this paper the patch data will be employed to make this comparison. These... 

The calculation of exposure by the patch technique also assumes that deposition of pesticide is uniform over... 

Among the first dermal dosimeters used in exposure research were 4 x 4-in cellulose or gauze patches which were pinned to the outer and inner surfaces of clothing or vests which farm workers would wear during the application or re-entry phase of the smdy. These patches were easy to manufacture and when pinned to the shirt or pants of the worker made for an easily used dosimeter pad. The major advantage to the use of the patch to estimate worker exposure was this method s ability to differentiate the relative contributions of pesticide residues to different parts of the worker s body. This sampling technique in turn could lead to recommendations (i.e., the use of... 

Preliminary results using a fluorescent tracer, which was added to the spray tank at the same time as the pesticide (Guthion WP), indicated that the distribution of the tracer, and presumably the pesticide, was not uniform, emphasizing the difficulty in the placement of the patches (2) This tracer technique is currently being evaluated as a tool for quantitative exposure estimation. This could result in a more realistic measurement of pesticide contact on the skin and minimize the reliance on extrapolation from the patch data. 

Measurements were made of the concentration of pesticide in the breathing zone of the workers, on patches attached to the workers clothing, and in the urine of crew members. In the 2,4-D tests, comparisons were made between amounts found under normal spray operations and amounts found when techniques for limiting exposure were used including special instructions and the use of protective clothing consisting of hat, boots, gloves, and Tyvek coveralls. 

Participants also expressed concern over techniques for estimating dermal exposure such as the use of patches, and the interpretation of data generated from patch contamination. Patch exposure cannot be correlated with uptake by unprotected skin, nor with blood levels or urinary excretion (except in some cases such as the phenoxy herbicides). Among questions remaining are how to extrapolate the ratio between acute dermal and acute oral doses in animals to man, whether re-entry data will be needed for every pesticide in every crop or crop grouping for every geographic location, and whether humans can legally be used for dermal absorption studies. 

Only recently has the problem of the loss of pesticide from patches used In the field been addressed ( ). Many studies do not report laboratory or field recovery data for sampling substrates or comment on correction for recovery of the data (,9). Serat ( ) found that cotton gauze retained only 30% of extractable parathlon and 70% of extractable dlcofol under field conditions. He concluded that In the absence of adequate controls to determine the quantity of chemical lost from the fabric collectors there Is no assurance that the extracted depositions represent anywhere near the actual values. This factor seriously limits the usefulness of many older exposure studies. New techniques using fluorescent markers (10) are promising and will undoubtedly lead to more quantitative estimates of contact exposure. 

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