| Transferable Residues From Dog Fur and Plasma Cholinesterase Inhibition in Dogs Treated with a Flea Control Dip Containing Chlorpyrifos J. Scott Boone, John W. Tyler, and Janice E. Chambers Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA Abstract
We studied chlorpyrifos, an insecticide present in a commercial dip for treating ectoparasites in dogs, to estimate the amount of transferable residues that children could obtain from their treated pets. Although the chlorpyrifos dip is no longer supported by the manufacturer, the methodology described herein can help determine transferable residues from other flea control insecticide formulations. Twelve dogs of different breeds and weights were dipped using the recommended guidelines with a commercial, nonprescription chlorpyrifos flea dip for 4 consecutive treatments at 3-week intervals (nonshampoo protocol) and another 12 dogs were dipped with shampooing between dips (shampoo protocol) . The samples collected at 4 hr and 7, 14, and 21 days after treatment in the nonshampoo protocol averaged 971, 157, 70, and 26 µg chlorpyrifos, respectively ; in the shampoo protocol the samples averaged 459, 49, 15, and 10 µg, respectively. The highest single sample was about 7,000 µg collected at 4 hr. The pretreatment specific activities in the plasma of the dogs were about 75 nmol/min/mg protein for butyrylcholinesterase (BChE) , and 9 nmol/min/mg protein for acetylcholinesterase (AChE) . BChE was inhibited 50-75% throughout the study, and AChE was inhibited 11-18% in the nonshampoo protocol ; inhibition was not as great in the shampoo protocol. There was no correlation (p  0.05) between length of hair and residues measured that would explain the residue differences among dogs. Transferable residues had largely dissipated during the three weeks after treatment, with the largest decrease occurring during the first week. Greater plasma ChE inhibition was observed at 7 days than at 4 hr, probably reflecting the bioactivation of chlorpyrifos to chlorpyrifos-oxon. Plasma cholinesterase activity did not return to control levels during the 3-week period. The differences between the shampoo and nonshampoo protocols were explained by differences in the techniques of the dip applicators. Key words: acetylcholinesterase, butyrylcholinesterase, chlorpyrifos, dog fur, flea control, organophosphate insecticide, pesticide monitoring, transferable residues. Environ Health Perspect 109:1109-1114 (2001) . [Online 19 October 2001] http://ehpnet1.niehs.nih.gov/docs/2001/109p1109-1114boone/ abstract.html Address correspondence to J.S. Boone, Box 6100, Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762-6100, USA. Telephone: (662) 325-1079. Fax: (662) 325-1031. E-mail: jsboone@cvm.msstate.edu The authors thank H.D. Cantwell for the use of the animal facilities, S. Waldrop and T. Couch for the cholinesterase assays, K. Lebbin-Hanson for the chemical analyses, C. Boyle for statistical advice, C. Langston for advice on kinetic calculations, and C. Bates, C. Buisson, D. Dunaway, T. Kothstein, A. Smith, and C. Zickus for treatment and sampling of the dogs. The research was supported by a U.S. Environmental Protection Agency grant, EPA R-825170-01-0, and by the Mississippi Agriculture and Forestry Experiment Station (MAFES) under project number MISV-3403 and the College of Veterinary Medicine, Mississippi State University. This article is MAFES publication number J-9617 and Center for Environmental Health Sciences publication number 102. Received 17 November 1999 ; accepted 11 April 2001.
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