Ecotoxicological Effects of Pharmaceuticals and Personal Care Products on the Microbiome and Oxidative Stress of Freshwater Crayfish Faxonius obscurus.

The ecotoxicity of individual pharmaceuticals and personal care products (PPCPs) in freshwaters is well documented. However, their combined effects as mixtures on aquatic animals and their associated microbiomes remain poorly understood. This study examined the response of freshwater crayfish, Faxonius obscurus, to a mixture of three frequently co-occurring PPCPs, i.e., carbamazepine, estradiol, and triclosan, at environmentally relevant concentrations (10 or 100 μg/L). Our results revealed dose-dependent disruptions of crayfish microbiomes across multiple body locations upon a 96-hr PPCP exposure. These were characterized by an increase in the Firmicutes/Bacteroidetes ratio, an enrichment of opportunistic pathogens (e.g., Staphylococcus), and an elimination of commensal taxa (e.g., Dechloromonas). The taxonomic changes were accompanied by the enrichment of microbial detoxification and oxidative stress response pathways. Meanwhile, systemic oxidative stress was induced in the host crayfish across the carapace, gill, and abdominal muscle. Our findings underscore the urgent need for mixture-based monitoring efforts and risk assessments in environmental management to better protect freshwater ecosystems from the cumulative ecotoxicity of PPCPs.