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In vivo dermal absorption of pyrethroid pesticides in the rat.
Hughes, M. AND B. Edwards. In vivo dermal absorption of pyrethroid pesticides in the rat. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. Taylor & Francis, Inc., Philadelphia, PA, 79(2):83-91, (2016).
What is the study? We examined the in vivo dermal absorption of the pyrethroid pesticides bifenthrin, deltamethrin and permethrin in the Long-Evans male rat. The pyrethroids were radiolabelled. We had previously published an in vitro dermal absorption study with these same pyrethroids and animal model. We also included data from human cadaver skin. In the in vivo study, the animals were dosed on the back with the pyrethroid. The animals were placed in metabolism cages to collect excreta. At 24 h post-exposure, the treated skin was washed to remove unabsorbed pyrethroid. One group of animals were euthanized. Another group was placed back in the metabolism cages to collect excreta for 4 additional days. These animals were then euthanized. Excreta and tissues collected from the euthanized animals and analyzed for radioactivity. Why was it done? Pyrethroid pesticides are more commonly used today because of the phase out of organophosphate pesticides. One of the ways human are exposed to pesticides is by the dermal route. Dermal exposure to pesticides can occur during the spraying of pesticides or contacting contaminated surfaces. The information on the in vivo dermal absorption of pyrethroid pesticides is limited. What is the impact to the field and Agency? Using the data from this experiment and the data from our previous in vitro dermal absorption study, we estimate the in vivo human dermal absorption of these three pyrethroid pesticides to be less than 10%.
The potential for exposure to pyrethroid pesticides has risen recently because of their increased use. The objective of this study was to examine the in vivo dermal absorption of bifenthrin, deltamethrin and permethrin in the rat. Hair on the dorsal side of anesthetized adult male Long-Evans rats was clipped with an electric razor. The next day, the rats were anesthetized and dosed on the skin with 1750 nmole (312.5 nmole/cm2) of radiolabeled (5 uCi) bifenthrin, deltamethrin or permethrin applied in acetone. A non-occluding plastic cover was glued to the skin over the dosing site. The animals were placed in individual metabolism cages to collect urine and feces. At 24 h post-dosing, the rats were anesthetized and the dosing site was washed with soap and water. One group of rats were euthanized by cardiac puncture and tissues were collected. The washed skin was removed from the euthanized rats and tape stripped. A second group of animals were returned to the metabolism cages after the wash for 4 additional days. Five days after exposure these animals were euthanized and tissues were removed. The excreta, skin wash, tape strips, tissues and carcass were analyzed for pyrethroid-derived radioactivity. Greater than 50% of the applied dose for the 3 pyrethroids was removed by the wash. The next highest percentage of the dose was detected in the skin, ranging from 9 to 24%. Cumulative radioactivity in excreta (urine + feces) ranged from 0.5 to 7% at 24 h and 3 to 26% at 120 h. Less than 0.3% of the dose for each of the pyrethroids was detected in the internal tissues analyzed, while the carcass retained 2 to 5%. Assuming absorption is equal to the cumulative recovery in skin (washed and tape stripped), excreta, tissues, and carcass, absorption was permethrin ~ bifenthrin > deltamethrin at 24 h and permethrin > deltamethrin > bifenthrin at 120 h. Human dermal absorption of these pyrethroids was estimated using the parallelogram approach with previous published in vitro data. It was estimated that human dermal absorption is < 10% of the dose applied to skin.