When registering a new pesticide active ingredient (AI), sub-chronic 90-day oral toxicity studies performed both on both a rodent and non-rodent species, typically rats and dogs, are standard testing requirements in most countries and are intended to be representative of shorter-term non-occupational and occupational pesticide exposures.  To determine how often the 90-day dog study was selected as the point of departure (POD) for assessing risk from non-dietary exposures, human health risk assessments (RAs) for 163 pesticide AIs registered by the U.S. Environmental Protection Agency from 1998 to 2021 were obtained from public sources and reviewed.  The dog study was used in RA for only 40 (25%) of the pesticides analyzed, 36 of which the dog no-observed-adverse-effect-level (NOAEL) was lower than the 90-day rat study NOAEL.  Dose spacing and/or allometric body weight scaling could account for lower NOAELs in dogs compared to rats for 23 of these 36 AIs, suggesting that the dog was more sensitive than the rat for only the remaining 13 pesticides. For some of the 13 AIs, however, studies of appropriate duration were available that had NOAELs comparable to the dog and would have offered a similar level of protection if used as the POD.  Overall, impacts to RA in terms of human health protection were minimal for nearly all 40 AIs in the absence of the 90-day dog study, but in a few cases identification of important hazards or setting of safe exposure levels would have been affected.  The results support the conclusion that in nearly all cases the 90-day dog study does not add materially to pesticide risk decisions.  This analysis provides a firm foundation for further work on developing criteria for determining when the dog study may be needed and when it can be waived for new pesticide registrations

Value of the 90-day dog study in human health risk assessment of agricultural pesticides

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