Effects of antidepressant exposures on a stream detrital food chain: Microbial decomposers and invertebrate detritivores

Antidepressants are often found in freshwater ecosystems, yet their potential impacts on ecological processes and species interactions remain poorly understood. This study assessed the ecological influence of fluoxetine and amitriptyline at environmentally realistic levels (1-100 ng L^-1) on a detritus-based food chain that encompasses microbial decomposers and freshwater snails. In the experiment, we monitored the responses of microbial decomposers (biomass and enzyme activity), and Cipangopaludina cathayensis (consumption rates and antioxidant capacity), as well as leaf litter traits (decomposition rate and nutrient content). After 30 days of exposure, fluoxetine at concentrations of 1 and 10 ng L^-1 significantly inhibited the activities of leucine aminopeptidase, glycine aminopeptidase and N-acetylglucosaminidase, thereby reducing the river snail's ability to extract nitrogen from leaves. The activities of β-glucosidase and polyphenol oxidase were significantly inhibited by amitriptyline at concentrations of 10 and 100 ng L^-1, which may reduce leaf palatability and subsequently decrease the consumption rate of the river snail. Furthermore, fluoxetine at 1 ng L^-1 and amitriptyline at 10 ng L^-1 affected the river snail by triggering an antioxidant stress response, leading to a significant increase in the activities of glutathione peroxidase and superoxide dismutase. Thus, fluoxetine and amitriptyline exhibited different bottom-up effects on the detrital food chain by acting on distinct microbial enzymes. Consequently, this study demonstrates that antidepressants disrupt key ecosystem processes, impacting nutrient cycling and freshwater ecosystem health.