Short-term to long-term extrapolation of lethal effects of an herbicide on the marine mysid shrimp Americamysis Bahia by use of the General Unified Threshold Model of Survival (GUTS).

Risk assessments for plant protection products and their active ingredients that are based on standard laboratory tests performed under constant exposure conditions may result in an overestimation of risks because exposure in the environment is often characterized by a few short peaks. Here, the General Unified Threshold Model of Survival (GUTS) was used to conduct a refined risk assessment for the herbicide tembotrione and its effects on the marine invertebrate Americamysis bahia, for which the standard chronic effect assessment failed. The GUTS model was first calibrated with time-to-effect and concentration-response data from 2 independent acute experiments with A. bahia. Model parameters for both toxicodynamic assumptions of stochastic death (SD) and individual tolerance (IT) were estimated with the reduced GUTS model (GUTS-RED) using the scaled internal concentration as a dose metric. Both the calibrated GUTS-RED-SD and GUTS-RED-IT models described survival dynamics well. Model validation using datasets of 2 independent chronic tests yielded robust predictions of long-term toxicity of tembotrione on A. bahia, with GUTS-RED-IT being more reliable than GUTS-RED-SD. The validated model was subsequently used to predict survival from time-variable exposure profiles, as derived from the FOrum for Co-ordination of pesticide fate models and their USe (FOCUS). Because ecotoxicological independence of peaks had not been empirically verified, the link between exposure and effects was assessed with complete exposure profiles. Effect thresholds resulting from different peak exposure concentrations and durations were determined with GUTS and directly compared with the exposure concentrations from the FOCUS surface water scenarios. The derived values were higher than the predicted FOCUS critical concentrations. Additionally, comparing the areas under the curve (AUCs) derived with GUTS for multiple peak exposure profiles to those from FOCUS revealed significant additional safety margins, demonstrating that only unrealistically high exposure concentrations would produce significant effects. In conclusion, no unacceptable effects of tembotrione on aquatic invertebrates under realistic environmental exposure conditions are expected. Integr Environ Assess Manag 2019;15:29-39. © 2018 SETAC.