Dislodgeability of chlorpyrifos and fluorescent tracer residues on turf: comparison of wipe and foliar wash sampling techniques.

Residential use of pesticides has increased substantially in the United States over the past twenty years. Contact with pesticide-treated turf may result in dermal exposures, particularly among children. This study evaluated wipe sampling and foliar wash techniques to measure chlorpyrifos on turf following insecticidal treatments with Dursban 4E. Residues of the fluorescent tracer Uvitex OB were also measured as part of a larger study adapting video imaging analysis to children's exposure to pesticides. The wipe technique recovered an average of 0.50 microgram/cm2 of chlorpyrifos, or 1.5% of the initial deposit, and an average of 0.21 microgram/cm2 of tracer, or 6.1% of the initial deposit, from bluegrass turf 1-3 hours after application. The foliar wash technique recovered significantly more chlorpyrifos and tracer (1.3 micrograms/cm2, or 4.0% and 0.36 microgram/cm2, or 10.5%, respectively). The resulting chlorpyrifos/tracer ratio was also significantly greater for the foliar wash technique (4.6) than for the wipe sampling technique (2.6). Variability associated with each technique was similar. Chlorpyrifos dissipation on irrigated and non-irrigated plots was evaluated through collection of wipe and foliar wash samples at six time intervals over a 48 h period. Wipe technique results indicated that irrigated residues were significantly lower than non-irrigated during the first 6.5 h post-application; foliar wash residues were significantly lower on the irrigated plot during the first 3.5 h post-application. No effect of irrigation on dislodgeability of chlorpyrifos residues was observed after 24 h. The findings indicate that foliar wash sampling removes larger amounts of chlorpyrifos and fluorescent tracer residues from turf than wipe sampling, and would therefore produce higher estimates of potential exposure among children if used as a turf contact-transfer factor. They also demonstrate that foliar was sampling produces a higher relative transfer factor for video imaging analysis of skin exposure than does wipe sampling. Wipe sampling was found to be far simpler than foliar wash sampling in regard to both sample collection and analysis. Further investigations are required to determine the accuracy of these two techniques in estimating transfer of pesticides from turf to skin.