Determination of handwash removal efficiency: incomplete removal of the pesticide chlorpyrifos from skin by standard handwash techniques.

This study was designed to develop standard procedures whereby the removal efficiency of handwash techniques can be determined. A known amount of the insecticide chlorpyrifos (Dursban), was transferred to the hands of volunteers, which were washed by a standard technique. The following experimental variables were studied: time between exposure and washing, washing solvent, and skin loading. Ethanol removed only 30% of the chlorpyrifos on skin at loadings of approximately 7 micrograms/cm2, with residence time on skin having no effect. Prewashing with ethanol increased removal efficiency. A 10% isopropanol/distilled-water wash removed 43% immediately following exposure, and 23% one hour post-exposure, with skin loadings of approximately 12 micrograms/cm2. Removal efficiency immediately following contact decreased for lower skin loading levels (21-23% for loadings of 0.1-1 micrograms/cm2). These findings indicate that substantial amounts of the insecticide were either absorbed through or adsorbed to the skin, and that pesticide residue levels recovered by standard handwashing techniques are unlikely to represent accurate estimates of dermal exposure. Approximately two-fold to five-fold underestimations of exposure can occur for pesticides with handwash procedures similar to those tested. All experimental variables studied can each alter significantly the fraction of total pesticide on skin that handwashing removes. If handwashing is to be used to estimate dermal exposure in the workplace, appropriate laboratory-based removal efficiency studies should be conducted prior to field investigations. Further efforts should be made to develop accurate and reproducible hand measurement techniques.