Joint Toxicity and Molecular Mechanisms of Dinotefuran and Pymetrozine to Daphnia magna: An Experimental and Computational Toxicology Study.

Combined pesticide applications are ubiquitous in agricultural production, yet the joint toxic effects and associated molecular mechanisms of such mixtures remain largely elusive. Herein, we assessed the acute and chronic toxicities of dinotefuran (DNT) and pymetrozine (PMZ) to Daphnia magna under single-compound and binary-mixture exposures, quantified mixture interaction patterns via the MIXTOX model with Independent Action (IA) model, and elucidated the underlying molecular mechanisms by computational toxicology approaches. Results showed PMZ was 274-fold more acutely toxic than DNT, and mixture toxicity was strictly additive, consistent with IA predictions. Chronic co-exposure to PMZ and DNT induced severe additive reproductive toxicity: total offspring dropped from 497 ± 20 (control) to 27 ± 11, first brood was delayed to day 11, and brood number reduced to 3-5. Acetylcholinesterase (AChE) was suggested as a putative shared target, with binding free energies of DNT-AChE (-14.62 ± 1.74 kcal/mol) and PMZ-AChE (-18.34 ± 2.82 kcal/mol); DFT calculations revealed electronic differences explaining their binding discrepancies. This study addresses the critical data gap in understanding the joint toxicity of DNT and PMZ mixtures, and provides robust experimental and theoretical support for the ecological risk assessment of pesticide co-exposures in aquatic environments.