Bioconcentration, metabolism, and biomarker responses in freshwater fish Carassius auratus exposed to roxithromycin

• ROX in water could accumulate in crucian carp, particularly in liver and bile.
• Seventeen metabolites were detected in bile.
• A plausible scheme for biotransformation pathways of ROX in fish was depicted.
• ROX could induce change of biomarkers, which related to ROX or its metabolites.

To investigate the distribution, bioconcentration, metabolism, and biomarker responses of macrolide antibiotic roxithromycin (ROX) in fish, crucian carp (Carassius auratus) were exposed to various concentrations of ROX (4, 20, and 100 μg L−1) for 20 d. The ROX content in different tissues was quantified using UPLC/MS/MS. The liver exhibited the highest ROX concentration followed by the bile, gills, and muscle tissues. After 15 d of exposure to different concentrations of ROX, the bioconcentration factors were 2.15–38.0 in the liver, 0.950–20.7 in the bile, 0.0506–19.7 in the gill, and 0.0439–13.8 in the muscle; these results were comparable to the estimated BCF values. The metabolites formed in the bile were identified based on metabolic identification in human bile. Additionally, the biomarkers, including acetylcholinesterase in the brain, as well as 7-ethoxyresorufin O-deethylase and superoxide dismutase in the liver changed significantly after 5, 10, 15, and 20 d of exposure (P < 0.05). Our results suggest that ROX can accumulate and be metabolized in fish; therefore, interactions between ROX or its metabolites and the biological systems may induce biochemical disturbances in fish.

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