Kotsiri_2026_Environ.Sci.Pollut.Res.Int__

Emerging contaminants such as pharmaceuticals and microplastics can potentially interact with marine biota through their entry into the marine environment via sewage treatment plants. Moreover, microplastics can sorb pharmaceuticals potentially affecting their uptake by marine species. This study aims to assess sublethal effects of two widely used pharmaceuticals, i.e., clarithromycin, an antibiotic, and venlafaxine, an antidepressant, separately and in combination with polystyrene (PS) microplastics in mussels Mytilus galloprovincialis under experimental conditions. Measurements of biomarkers reflecting oxidative stress [catalase (CAT), lipid peroxidation measured as thiobarbituric acid reactive substances (TBARS)], biotransformation [glutathione-S-transferases (GSTs)] and neurotoxicity [acetylcholinesterase (AChE)] were caried out in mussels that were exposed for 29 days to nominal concentrations of 1.5 microg/ L clarithromycin, 0.5 microg/ L venlafaxine, 0.8 mg/ L PS microplastics and their mixture. Elevated CAT activities were found in mussels exposed to clarithromycin and venlafaxine alone but not in those exposed to PS microplastics and their mixture with the two pharmaceuticals, and the same tendency although not significant was observed for lipid peroxidation. These results indicate oxidative stress related effects of clarithromycin and venlafaxine are diminished when mussels are exposed to clarithromycin and venlafaxine in combination with PS microplastics. AChE responses were only evident in PS exposed mussels while GSTs activities variations among treatments were not significant. The Integrated Biomarker Response (IBR) index indicated a trend of increased overall stress in mussels exposed to clarithromycin, venlafaxine and PS microplastics alone in comparison to their mixture. Results can contribute to understanding effects of pharmaceuticals and microplastics in marine organisms as well as their potential interactions.