The influence of moisture on indoor pesticide exposure of humans using chlorpyrifos, a model semi-volatile pesticide

Homeowners and professional applicators frequently use chemicals to control insect pests in urban environments. The identification and evaluation of determinants of human exposure are critical to conduct reliable and responsible human exposure assessments following indoor residential chemical applications. Three related studies are presented using chlorpyrifos (CP) as a model semi-volatile pesticide to evaluate moisture as a determinant of human exposure.; Evaluation of the influence of moisture on pesticide transferability and potential human exposure followed a CP and two water-only applications (after 24 and 48 hours) made to nylon carpet. Total chemical residue remained a stable source of CP. Transferable chemical residue measured using the California roller (Ross et al., 1991) declined rapidly following the CP and two water-only applications. The decline in transferable chemical residue correlated significantly with the percent carpet moisture (ca. 0.5--10%).; The in vitro effect of sweat on dermal absorption was studied using penetration-evaporation cells to measure percutaneous absorption. Cells received artificial sweat or were left "dry" prior to application of 14C-CP-treated carpet fiber. Sweat did not increase percutaneous absorption, but resulted in more radiolabel recovered after 24 hours from the epidermis and tape stripping the skin surface.; The effect of sweat on absorbed dose in humans was evaluated with human volunteers that participated in a structured activity program (SAP). Participants (n = 20) performed a warm-up exercise to induce light sweating prior to a SAP on CP-treated nylon carpet (Ross et al., 190; Krieger et al., 2001). Absorbed daily dosages (ADDS) were calculated using urinary biomonitoring of trichloropyridinol. Participation in the warm-up exercise prior to the exposure SAP resulted in an increased ADD of CP equivalents by approximately 50% (n = 2). Measured ADDS averaged 2.8 and 2.0 mug CP equivalents/kg/day in volunteers who participated in the warm-up exercise prior to exposures 1 and 2, respectively. In participants who rested prior to the exposures, ADDs were significantly lower at 1.9 and 1.3 mug CP equivalents/kg/day. These values were less than estimates of ADD made from CP deposition, the California roller, and clothing dosimeters worn by participants.; These studies indicate that moisture is an important determinant of contact transfer and human exposure.