Two-Compartmental Toxicokinetic Model Predicts Interspecies Sensitivity Variation of Imidacloprid to Aquatic Invertebrates

A two-compartmental toxicokinetic modelelucidates the interspeciessensitivity of imidacloprid to various aquatic invertebrates by distinguishingthe toxicologically relevant levels in the organisms. Interspecies sensitivity to the same chemical can beseveral ordersof magnitude different. Quantifying toxicologically internal levelsand toxicokinetic (TK) parameters is critical in elucidating the interspeciessensitivity. Herein, a two-compartmental TK model was constructedto characterize the uptake, distribution, and elimination kineticstoward interspecies sensitivity to an insecticide, imidacloprid. Imidaclopridexhibited the highest lethality to the insect Chironomusdilutus, followed by Lumbriculus variegatus, Hyalella azteca, and Daphnia magna. Interspecies sensitivity of imidaclopridto these invertebrates varied by & SIM;1000 folds based on waterconcentrations (LC50). Remarkably, the sensitivity variation decreasedto & SIM;50 folds based on the internal residues (LR50), highlightingthe critical role of TK in interspecies sensitivity. A one-compartmentalTK model failed to simulate the bioaccumulation of imidacloprid inthese invertebrates except for D. magna. Instead, a two-compartmental model successfully simulated the slowelimination of imidacloprid in the remaining three species by internallydistinguishing the highly dynamic (C (1))and toxicologically available (C (2)) fractions.We further showed that the species sensitivity of the invertebratesto imidacloprid was significantly related to C (2), demonstrating that C (2) was toxicologicallyavailable and responsible for the toxicity of imidacloprid. This mechanistic-basedmodel bridged the internal distribution of organic contaminants insmall invertebrates and the associated toxic potency.

Automated summary

A two-compartmental toxicokinetic model is used to explain the interspecies sensitivity of imidacloprid to different aquatic invertebrates by distinguishing relevant levels of toxicity in organisms. The sensitivity to imidacloprid can vary significantly among different species. Internal levels of toxicity and toxicokinetic parameters are essential in understanding interspecies sensitivity. The model demonstrates that imidacloprid exhibits the highest toxicity to Chironomus dilutus, followed by Lumbriculus variegatus, Hyalella azteca, and Daphnia magna. The sensitivity of these invertebrates to imidacloprid varies by over 1000 times based on water concentrations, but decreases to around 50 times when based on internal residues, highlighting the importance of toxicokinetics in interspecies sensitivity. The two-compartmental model successfully simulates the slow elimination of imidacloprid in three species by distinguishing dynamic and toxicologically available fractions.