Final Report: Assessing Levels of Organophosphorus Insecticides Which Could Expose Children From Pets Treated with Flea Control Insecticides

EPA Grant Number: R825170
Title: Assessing Levels of Organophosphorus Insecticides Which Could Expose Children From Pets Treated with Flea Control Insecticides
Investigators: Chambers, Janice E. , Boone, J. Scott , Tyler, John W.
Institution: Mississippi State University - Main Campus
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999
Project Amount: $597,804
RFA: Exposure of Children to Pesticides (1996) RFA Text |  Recipients Lists
Research Category: Pesticides , Children's Health , Health Effects , Health , Safer Chemicals


The objective of this project was to determine the levels of transferable insecticide residues that could be transferred to humans from dogs treated with flea control dips or collars. The flea control dips and collars selected for study were non-prescription (over the counter) products that were commercially available at the time the experiments were initiated. All products selected for study contained an organophosphorus insecticide. The overall design of the project was to sample for transferable residues by rubbing the fur of dogs for a 5 minute period along a 10 inch length of the dog's back along the midline using a white cotton glove. Privately owned dogs of a variety of breeds were recruited by requesting owners to volunteer their pet dogs for the experiments. The dogs were initially shampooed prior to initiation of the experiments to remove any insecticide residues that might have been present in their fur. The pet owners were asked not to use any organophosphorus insecticides on the pets or in the household during the course of the experiments.

The initial product studied was a chlorpyrifos-containing dip (Adams Flea and Tick Dip), which was administered according to package directions at 3 week intervals. Because there was a possibility that residues from a previous dip might still be present when subsequent dips were administered, and an accumulation of the insecticide might occur, the study design included half of the animals which would be shampooed before each successive dipping, while the other half of the animals were not shampooed at intermediate times. Fur residue samples were taken at weekly intervals during the experimental period. In addition, blood samples were taken from the dogs for plasma cholinesterase analysis to test for internalization of the insecticide by the dog. There were 12 replications in the non-shampoo protocol and 12 replications in the shampoo protocol.

The second product tested was a phosmet-containing dip (Paramite Dip), which was administered four times at 2 week intervals as indicated by package directions. Because the initial experiments with chlorpyrifos indicated that insecticide residues had dissipated prior to the next dipping interval, no intermediate shampooing was performed with this dip. Animals were handled as in the previous experiment. There were 24 replications.

The third product studied was a tetrachlorvinphos (Rabon)-containing collar, with sampling occurring periodically for 112 days following placement of the collar. The fourth product studied was a chlorpyrifos-containing collar, with sampling occurring periodically for 168 days following placement of the collar. Dogs were shampooed monthly during these long sampling intervals for the sake of hygiene. In addition to the sample obtained from the fur of the back, samples were taken on the neck with the collar removed and on the neck with the collar in place.

Gloves were pre-extracted prior to use to remove any potentially interfering chemicals. After use in sampling the dogs, gloves were extracted with organic solvents (using an Accelerated Solvent Extractor, ASE), and the levels of insecticide were quantified by gas chromatography with electron capture detection. Serum cholinesterase was assayed for enzyme inhibition using a standard spectrophotometric methodology (Ellman technique).

In addition to the above research which was sponsored by the EPA STAR grant, some additional funding was obtained from some of the flea collar manufacturers to expand the chlorpyrifos collar study to include the quantitation of urinary metabolites in adults and children in the households of the pet dogs. Urine samples (first morning void) were taken and extracted and the levels of trichloropyridinol (TCP), the metabolite of chlorpyrifos, were measured by ELISA methods.

All appropriate Institutional Animal Care and Use Committee (IACUC) approvals were obtained prior to initiation of the experiments. All appropriate Institutional Research Board (IRB) approvals were obtained prior to involvement of any human subjects in the research, and the consent of adults and the assent of all children were obtained from all providing urine samples.

Summary/Accomplishments (Outputs/Outcomes):

The transferable residues obtained in the gloves used to rub the fur of the dogs with both chlorpyrifos and phosmet from their respective dips were found to peak shortly after the dip administration and to dissipate during the time interval prescribed by the dip label directions, i.e., 3 weeks for chlorpyrifos and 2 weeks for phosmet. By the end of these intervals, there were negligible transferable residues measured on the gloves. Therefore there was no evidence of any accumulation of insecticide from one dipping to the next in the fur of the dogs which might create an increasing likelihood of exposure of humans to these insecticides with repetitive use of these products. Peak residues measured in the gloves from the chlorpyrifos dip were 1.23 mg (range 0.16 to 7.00 mg) for the 5 minute rubbing period and for phosmet were 2.84 mg (range 0.08 to 11.62 mg). Variability was high in the residues, as expected, since the design specified use of a variety of types of dogs. Plasma cholinesterase activity was inhibited about 60% compared to pre-test samples in the dogs treated with the chlorpyrifos dip, with some incomplete recovery of cholinesterase activity occurring between the dippings. In contrast, no appreciable cholinesterase inhibition was observed with the phosmet dip. These cholinesterase data suggest that chlorpyrifos was being internalized by the dogs, whereas phosmet was not or alternatively that phosmet is a weak inhibitor of dog plasma cholinesterase.

The tetrachlorvinphos and chlorpyrifos collar both yielded the least transferable residues in the glove samples taken at the back, intermediate residues from the neck with the collar removed and the highest residues from the neck with the collar in place, as predicted. The data indicated that only relatively small amounts of insecticide migrate in the fur from the collar to distant portions of the dog's body; therefore, not all regions of the dog will be of equivalent likelihood of contamination of people following their contact with the dog. As was true for the dips, there was an appreciable degree of individual variation in the residues obtained among the test dogs.

The tetrachlorvinphos collar resulted in very high transferable residues from the neck region of the dog when the collar was in place. These residues peaked at about 1 week after application of the collar, with gradual dissipation over the subsequent weeks. Peak transferable residues at 3 days for the posterior back region were 0.26 mg (range 0.01 to 1.02 mg), and at 7 days for the neck with collar removed 8.67 mg (range 1.16 to 17.31 mg) and for the neck with the collar in place 24.04 mg (range 8.06 to 77.07 mg). There was negligible inhibition of the plasma cholinesterase in the dogs.

In contrast, the chlorpyrifos collar resulted in a rise in transferable residues during the first week after collar application, followed by rather similar transferable residues throughout the remainder of the sampling period. The residues were considerably lower than those obtained with tetrachlorvinphos. Peak residue levels were 0.005 mg on the posterior back, 0.17 mg on the neck with the collar removed, and 0.30 mg on the neck with the collar in place. Plasma cholinesterase activities in the dogs were inhibited about 60% compared to pre-test activities throughout the sampling period. Urine samples from the adult and the child in the households of these dogs indicated that there were low TCP levels present before the collar was placed on the dogs, presumably from exposure to chlorpyrifos from a variety of other agricultural and/or residential uses of chlorpyrifos. While there appeared to be a possible rise in urinary TCP levels in the urine samples from both the children and the adults, variability among individuals was high and there were no statistically significant differences in TCP levels between samples after the collar was placed on the dog to those before the collar was placed on the dog. Adjusting the TCP levels for urinary creatinine concentrations did not reduce the variability of the values appreciably, and there were still no statistically significant differences in the pre- and post-collar samples.


There were appreciable residues of both chlorpyrifos and phosmet that were transferable from the fur of dogs treated with dips containing these insecticides. The residues dissipated to negligible levels during the 2-3 weeks following the dipping, and there was no evidence of a build-up of residues at the time of the next dipping as recommended by the label directions. Plasma cholinesterase activity in the dogs indicated that chlorpyrifos was absorbed by the dogs and that the activity failed to recover prior to the next dipping, whereas there was no evidence of inhibition following phosmet use, which may indicate that phosmet was not internalized by the dog.

Residue levels obtained from rubbing over a tetrachlorvinphos collar were very high, in the 20 mg range at the time of peak residues. While these levels seem to be of some potential concern, there was no evidence of plasma cholinesterase inhibition in the dogs, so there was no evidence of absorption by the dogs. It is possible to assume, from these data in dogs, that people would not be a risk of cholinesterase inhibition either. Residue levels obtained from the dogs treated with the chlorpyrifos collar were considerably lower than those from the tetrachlorvinphos collar; however, appreciable and prolonged plasma cholinesterase inhibition was observed in the dogs, indicating that internalization of the insecticide by the dogs was occurring during the several months of the experiment. There were no statistically significant increases in the urinary levels of TCP (one of the hydrolysis products of chlorpyrifos) in either adults or children (aged 3 to 12 years) living in the households of these pet dogs. Therefore there is no evidence that flea collars containing chlorpyrifos used on pet dogs is a source of exposure of people to this insecticide. The data from both collars indicate that the highest residues were obtained by contact with the collar itself, and that only very low levels migrated to the distant areas of the dog's body.

The data were highly variable, as was expected. It was the intent of these experiments to monitor pet dogs of a variety of types, and not consistent experimental animals, to give a realistic range of potential exposure levels. These experiments were designed to give the best range of data for potential probabilistic approaches in risk analysis.

The EPA regulators in the Office of Pesticide Programs have used the information from the chlorpyrifos collar experiments in their recent risk assessment of chlorpyrifos, so these data have contributed to the cumulative risk assessments now being conducted under the Food Quality Protection Act. Additionally, it is our understanding that the glove protocol developed in this project has been incorporated into OPP's Standard Operating Procedures in its residential exposure analysis methods descriptions.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other project views: All 5 publications 1 publications in selected types All 1 journal articles
Type Citation Project Document Sources
Journal Article Boone, J.S., J.W. Tyler, and J.E. Chambers. 2001. Transferable residues from dog fur and plasma cholinesterase inhibition in dogs treated with a flea control dip containing chlorpyrifos. Environ. Hlth. Perspect. 109:1109-1114. R825170 (Final)
not available

Supplemental Keywords:

exposure assessment; residential exposure assessment; pesticide exposure to children., RFA, Health, Scientific Discipline, Toxics, Environmental Chemistry, Health Risk Assessment, pesticides, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, Children's Health, genetic susceptability, health effects, pesticide exposure, risk assessment, sensitive populations, dermal exposure, adult reference dose, Phosmet, health risks, infants, age-related differences, chlorpyrifos, dermal contact, dogs, measuring childhood exposure, exposure, pets, air pollution, children, assessment of exposure, children's vulnerablity, susceptibility, toxicity, human exposure, insecticides, pesticide residues, exposure pathways, harmful environmental agents, dietary exposure, flea control insecticides, organophosphate pesticides

Relevant Websites:

Synthesis Report of Research from EPA’s Science to Achieve Results (STAR) Grant Program: Feasibility of Estimating Pesticide Exposure and Dose in Children Using Biological Measurements (PDF) (42 pp, 3.87 MB)

Progress and Final Reports:

Original Abstract
  • 1997
  • 1998 Progress Report