Use of Foliar Transfer Coefficients in Conjunction with PBPK/PD Models in Assessing Absorbed Dose and ChE Inhibition from Post Application Dermal Exposure to Pesticides on Citrus and Turf. J. B. Knaak, State University of New York at Buffalo; C. Dary, USEPA; G. T. Patterson, California Department of Pesticide Regulation; and J. Blancato, USEPA
The early work of Popendorf and Leffingwell (Residue Rev. 82, 125 (1982)) and Nigg et al. (Am Ind. Hyg. Assoc. J. 45, 182 (1982)) on the transfer of pesticide foliar residues led to the adoption of standard operating procedures (SOPs) for estimating exposure from dermal contact by EPA. According to an SOP entitled "Postapplication dermal exposure to pesticide residues while harvesting fruit from trees", daily work place exposures (mg/kg) and dose (mg/kg/day) may be estimated using pesticide dislodgeable leaf residue data (DFRs) and crop dislodgeable residue transfer coefficients (Tcs). Exposure (Ed, mg/kg) and absorbed dose (Dd, mg/kg BW) are calculated by equations 1) Ed = (DFR x CF x Tc x ET) and 2) Dd = (Ed/BW) x Ad. EPA’s default value of 100% for dermal absorption (Ad) and California’s default value of 50% based on an experimental saturation model suggested that percutaneous absorption PBPK/PD models would provide better estimates of Ad and adverse effects. An isofenphos dermal PBPK/PD model developed by Knaak et al. (ACS Symposium Series 643) was used in conjunction with a new dermal model developed for parathion to assess Ad and ChE inhibition. This was accomplished by using the foliar transfer coefficients, Tcs, of 10000 cm2/h for the transfer of parathion residues from citrus and isofenphos residues from turf to skin. According to the models, 3% of the transferred residues were absorbed during an 8 h day in citrus or 2 h on turf. Foliar parathion and isofenphos residues of 0.09 ug/cm2 and 0.6 ug/cm2, respectively, produced little or no ChE inhibition in exposed individuals.
The USEPA, through its Office of Research and Development, participated in this research and approved this abstract as a basis for an oral presentation. The actual presentation has not been peer reviewed by the EPA.
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