Permethrin is registered for use on/in numerous food/feed crops, livestock and livestock housing, modes of transportation, structures, buildings (including food handling establishments), Public Health Mosquito abatement programs, and numerous residential use sites including use in outdoor and indoor spaces, pets, and clothing (impregnated and ready to use formulations).
According to Agency data, approximately 2 million pounds of permethrin are applied annually to agricultural, residential and public health uses sites. The majority of permethrin, over 70%, is used in non-agricultural settings; 55% is applied by professionals, 41% is applied by homeowners on residential areas, and 4% is applied on mosquito abatement areas.
Permethrin is a restricted use pesticide for crop and wide area applications (i.e., nurseries, sod farms) due to high toxicity to aquatic organisms, except for wide area mosquito adulticide use. It is a general use pesticide for residential and industrial applications.
Permethrin also has non-FIFRA pharmaceutical uses as a pediculicide for the treatment of head lice and scabies. The Food and Drug Administration (FDA) approves use of the pesticide-containing pharmaceutical under FFDCA.
Acute, chronic non-cancer, and cancer dietary (food and drinking water) risks from permethrin were below the Agency’s level of concern (LOC).
All non-cancer (dermal and inhalation) risks for individuals handling permethrin products in a residential setting were below the Agency’s LOC. All cancer risk estimates were also below the Agency’s LOC, except for the following scenario: mixing/loading/applying the EC formulation via sponge to horses.
The non-cancer post-application risk estimates for adults and youth aged children exposed to an environment treated with permethrin were below the Agency’s LOC; however, the risk estimate for toddlers exposed to permethrin treated indoor surfaces (carpets) were above the Agency’s LOC. The cancer risk estimates for adults exposed to indoor surfaces treated with permethrin from directed surface sprays or total release foggers were also above the Agency’s LOC.
The Agency considered post-application exposure to both outdoor residential misting systems and permethrin treated clothing. All scenarios were below the Agency’s non-cancer and cancer LOCs.
The acute aggregate risk non-cancer and cancer estimate from food and drinking water does not exceed the Agency’s LOC.
Aggregate short-term (1-30 days) non-cancer risk estimates, which include the contribution of risk from chronic dietary sources (food + drinking water) and short-term residential sources, exceeded the Agency’s LOC for toddlers exposed to permethrin through food and drinking water, and through post-application exposure during high contact activities on lawns and indoor surfaces. The risk
driver for the aggregate non-cancer risk estimate was post-application exposure to permethrin on treated indoor surfaces (carpets).
The aggregate cancer risk estimate exceeded the Agency’s LOC for adults exposed to permethrin through food and drinking water, and through postapplication exposure during high contact activity on lawns and indoor surfaces. Similar to the non-cancer aggregate risk assessment, post-application exposure to treated indoor carpets was the risk driver.
All residential/recreational exposures are expected to be short-term in duration. Therefore, no intermediate-term (1-6 months) or long-term (>6 months) aggregate risk was assessed.
EPA believes that the appropriate way to consider the pharmaceutical use of permethrin in its risk assessment is to examine the impact that the additional nonoccupational pesticide exposures would have to a pharmaceutical patient exposed to a related (or, in some cases, the same) compound. Based on a worse case scenario assessment, EPA estimates that the permethrin exposure a patient is expected to receive from a typical single application of a 1% and 5% permethrin pharmaceutical cream, respectively, is 450 to 2300 times greater than the combined exposure from the dietary and other non-occupational sources of permethrin. FDA has reviewed these estimates and determined that pesticide exposure in patients receiving treatment with a pharmaceutical permethrin drug product would fall within the expected range of exposure following treatment with permethrin drug product alone, and would not present an increased safety risk.
The majority of occupational handler risk estimates were below the Agency’s non-cancer LOC at baseline personal protective equipment (PPE) (long-sleeve shirt, long pants, no gloves, and no respirator). For all other scenarios where the LOC was exceeded considering just baseline PPE, all occupational risk estimates were below the Agency’s non-cancer LOC with additional PPE or engineering controls.
The estimated cancer risks for the majority of grower scenarios were also within the negligible risk range (≤3 x 10-6) or less with baseline PPE and gloves. However, a number of scenarios result in risk in the 10-5 to 10-6 range at this level of PPE, and either require additional PPE before the cancer risk estimates were below the negligible risk range, have no data available to estimate risk, or further mitigation measures were not feasible.
For all agricultural post-application scenarios assessed, the non-cancer risks do not exceed the LOC (MOEs > 100) on the day of application, approximately 12 hours following application. Most of the post-application cancer risk estimated for both hired hands and commercial/migratory farm workers were in the 10-5 to 10-7 range. The highest risk estimates, in the 10-4 range, were for conifer seed cone harvesting and thinning of certain fruit trees.
All non-cancer post-application exposure scenarios for military personnel and garment workers exposed to permethrin-impregnated battle dress or fabric, respectively, do not exceed the Agency’s LOC. Further, all of the postapplication cancer risk estimates for both populations were in the 10-6 range.