A Moment of Heat, a Lifetime Exposure? Integrating Effects of Temperature and Heatwaves into Toxicokinetic Modelling of a Neonicotinoid in Aquatic Invertebrates

Chemical pollution and climate change are major threats towards aquatic communities. Yet, their interactions remain poorly understood. Recent studies described the temperature-dependent toxicokinetics of contaminants in aquatic invertebrates but showed limitations for elimination resistant contaminants such as the receptor-binding neonicotinoids. The present study examined temperature effects on toxicokinetics of the neonicotinoid thiacloprid in aquatic invertebrates to improve predictions of bioaccumulation from laboratory to field conditions.A recently developed two-compartment model including irreversible receptor binding was applied to reanalyze a dataset on the temperature dependency of the toxicokinetics of thiacloprid in Gammarus pulex and Hyalella azteca (50 µg L-1 at 6 - 21°C). The Arrhenius equation was used to describe the temperature dependency of the toxicokinetic rate constants. Model parametrization was supported by receptor-binding assays. To test the predictivity of the model under dynamic exposure conditions, additional experiments were carried out in experimental stream mesocosms spiked with thiacloprid (10 µg L-1) under natural ambient and heatwave (+8 °C) conditions (10 - 34 °C).The two-compartment model fitted laboratory data better (R2 = 0.78 – 0.98) than previously applied one-compartment models and the temperature dependency of toxicokinetic rate constants (Arrhenius temperature TA = 7200 to 8300 K−1) matched with physiological endpoints from previous experiments (8000 K−1). Implementing temperature effects into the toxicokinetic model accurately predicted tissue concentrations in the mesocosm experiment, thereby validating the model. The tissue concentrations were two times higher under heatwave conditions compared to ambient conditions (46 vs. 25 µg kg-1) and remained constant after the event of exposure.The present study advances the mechanistic understanding of chemical exposure and bioaccumulation under changing climatic conditions and highlights how extreme heat events can intensify risks caused by neonicotinoids. These findings emphasize the need for regulatory strategies, such as dynamic models, to address the interactions of contaminants and a warming climate.