Gut Microbiota-Associated Changes in Toxicokinetics of Imidacloprid across a Terrestrial Food Chain: Aggravated Transfer and Biotransformation upon Coexposure to ZnO-NPs

Agricultural applications of nanotechnologies inevitably introduce nanoparticles and pesticides into agroecosystems as complex mixtures, with unknown implications along terrestrial food chains. We investigated the joint effects of ZnO-NPs and imidacloprid (IMI) along a lettuce–snail food chain over 21days of uptake and 10 days of depuration, focusing on IMI biotransformation and the associated changes of gut microbiota. Coexposure to ZnO-NPs increased the uptake rate constants and the kinetic trophic transfer factor of IMI from lettuce to snail soft tissues by 1.98–2.14-fold and 1.78–1.92-fold, respectively. Higher biotransformation rate constants and 5-hydroxy-imidacloprid (5-OH-IMI) concentrations in mixture treatments suggested enhanced IMI metabolism under coexposure. IMI predominantly accumulated in soft tissues, whereas 5-OH-IMI was primarily excreted via feces, and Zn was retained in viscera. Coexposure was accompanied by larger shifts in gut bacteria and predicted xenobiotic-metabolism-related functional changes, which correlated with IMI and 5-OH-IMI toxicokinetic patterns. These findings underscore the relevance of nanoparticle–pesticide–microbiota–host interactions to agroecosystem risk assessment.