Utility of the avian sub‐acute dietary toxicity test in ecological risk assessment and a path forward to reduce animal use

Abstract

The United States Environmental Protection Agency (USEPA) has long required both avian sub-acute dietary and acute oral studies to inform risk assessments for pesticides. Recently, the USEPA collaborated with People for the Ethical Treatment of Animals to determine whether the results of the acute oral avian toxicity test or the sub-acute dietary toxicity test consistently generated the greatest risk predictions in USEPA tier 1 assessments for pesticides first registered between 1998 and 2017. Their study concluded that in 99% of the cases, risk conclusions were driven by the acute oral study (OPPTS 850.2100, OCSPP 850.2100, or similar) because using these data results in higher risk quotients than sub-acute dietary data. Shortly after publishing these results, the USEPA released a formal memorandum providing guidance for waiving the subacute dietary study for most pesticides. The USEPA will, however, retain the option to require sub-acute dietary studies for pesticides with certain chemical properties. However, as the avian sub-acute dietary study has an exposure regimen that is often more representative of how birds are exposed to pesticides under actual use conditions than does the acute oral study (i.e., as part of a dietary item eaten over the course of a day and not a bolus dose), this study can provide useful context for risk assessment on a case-by-case basis. Decision criteria are needed to determine a path forward that both minimizes vertebrate animal testing and positions the avian sub-acute dietary data as an option for risk refinement. Decision criteria are proposed here with recommendations for refining the design of avian sub-acute dietary studies to ensure that the data generated are optimized to support a science-based acute avian risk assessment, supported by a case study demonstrating when and how sub-acute dietary studies may be used in a higher-tier risk assessment.

Toxicological effects assessment for wildlife in the 21st century: Review of current methods and recommendations for a path forward

“…Although it seems that risk can be assessed with confidence in most cases using just the avian acute oral test (Hilton et al, 2019), subacute dietary studies are still conducted to meet registration requirements of other jurisdictions (e.g., Brazil), and because many products are developed with the intent of global registrations, such data are often still generated. Subacute dietary studies for birds offer a more realistic exposure route and feeding scenario (gorge feeding is less typical) and could be a valuable tool as part of a higher tier risk assessment framework (Bone et al, 2022). Furthermore, for some chemicals (e.g., anticoagulant rodenticides) hazard may be markedly underestimated by acute oral studies, as toxicity is enhanced with repeated exposure (Vyas & Rattner, 2012).…”