Calibration and validation of AQUATOX model using the General Unified Threshold model of Survival (GUTS) framework
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Recently the European Food Safety Authority (EFSA) issued a scientific opinion on the state of the art of Toxicokinetic/Toxicodynamic (TK/TD) models, and specifically General Unified Threshold model of Survival (GUTS) models and their use in environmental risk assessments for pesticides and aquatic organisms. AQUATOX is a risk assessment modelling framework which incorporates essential TK/TD constructs compiled from the literature and primary research which has undergone extensive peer review in the United States. It has been applied successfully in numerous cases for a variety of pesticide compounds, applied both individually as well as in combination (i.e. multiple stressors) with a variety of aquatic species. Since it is an aquatic ecosystem model, it also incorporates food web dynamics and tracks pesticide movement through the food chain. AQUATOX can be run to represent either external or internal toxicant concentrations of pesticides in a manner consistent with the EFSA scenarios. We have calibrated AQUATOX using the propiconazole dataset (Nyman et al. 2012) which was applied to simulate both a simple tank experiment with the amphipod species Gammarus pulex and a more complex food-chain simulation representing a pond scenario with G. pulex combined with other pond species including other vertebrates and fishes. The results for the simple tank simulation compare very favourably with the validation datasets used for several GUTS validation scenarios which demonstrate the utility of the AQUATOX framework in similar risk assessment scenarios. Both single concentration trials and pulsed trials results were very similar to the validation exercises described in the EFSA documentation. Some differences were observed in that AQUATOX models biomass therefore Gammarus populations continued to grow when toxicants were removed. While there were no data available to validate the pond food-chain experiment, the simulation illustrates the utility of AQUATOX in extending risk assessment scenarios beyond the simple lab experiment case. Discussion of the results and implications to real world comparisons will be illustrated.