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A Probabilistic Approach for Chronic Effects Assessments using Acute to Chronic Ratio Distributions in a Vernal Pool Case Study
Citation:
Oliver, L., S. Sinnathamby, Tom Purucker, AND Sandy Raimondo. A Probabilistic Approach for Chronic Effects Assessments using Acute to Chronic Ratio Distributions in a Vernal Pool Case Study. SETAC North America 43rd Annual Meeting, Pittsburgh, PA, November 13 - 17, 2022.
Impact/Purpose:
A novel probabilistic approach is demonstrated to estimate chronic pesticide effects on a listed aquatic invertebrate species using acute:chronic ratios derived from a chemical-specific database. By incorporating distributions developed for modeled environmental exposure concentrations and for acute toxicity of surrogate species, uncertainty of exposure and effects estimates can be integrated in assessments of risk to species for which little or no toxicity data exists.
Description:
Ecological risk assessments for potential pesticide impacts on listed species must ensure that decisions to grant registration will not jeopardize species or their critical habitats. Pesticides are designed to cause lethality to pest species via physiological pathways that are also shared by nontarget species for which toxicity data is usually unavailable, creating a need for robust methods to estimate acute and chronic toxicity with minimal data. We used a unique probabilistic approach to estimate risk of chronic effects of 2 organophosphate (OP) pesticides on the vernal pool fairy shrimp Branchinecta lynchi. Acute toxicity estimates were derived from Monte Carlo (MC) sampling of acute toxicity distributions developed from interspecies relationships using surrogate species. Within each MC draw, acute values were divided by an acute to chronic ratio (ACR) sampled from a distribution of ACRs for organophosphate (OP) compounds and invertebrates, producing a distribution of chronic effects concentrations. Probability of risk was characterized using MC simulations of exposure concentration distributions representing four seasonal scenarios. A deterministic chronic effects threshold was compared with the probabilistic method, demonstrating the deterministic estimate of chronic toxicity under-estimated chronic risk for two OPs, chlorpyrifos and diazinon. Demonstration of this approach for a focal species, the fairy shrimp B. lynchi, expands potential interpretation of risk to the vernal pool community level. By coupling a novel probabilistic approach for estimating chronic effects using ACRs with probabilistic exposure distributions, risk characterization that harnesses uncertainty in both exposure and effects is possible and applicable to higher-tiered listed species assessments.
