Application of the C-BED tool in the analysis of the effect of norfluoxetine as an EDC on the marine mussel <i>Mytilus trossulus</i>

Norfluoxetine (NFLU), a metabolite of the antidepressant fluoxetine, is a known persistent endocrine-disrupting chemical (EDC) detected in aquatic environments. This study applies the Coastal Biosensor for Endocrine Disruption (C-BED) transcriptomic tool to evaluate NFLU's effects on the marine mussel <i>Mytilus trossulus</i>. After an experiment in which mussels were exposed to 500 ng/L NFLU for six days, gonads from both sexes were analyzed for C-BED gene expression. Significant sex-specific changes were observed in the expression of genes encoding caveolin 3 (CAV-3) serotonin receptor (SR) and membrane-bound transcription factor protease (MBTP). NFLU downregulated CAV-3, SR, and MBTP in male gonads but upregulated CAV-3 and SR in females, with the largest change being a 21-fold decrease in CAV-3 expression in males and a 14.6-fold increase in females. These findings demonstrate that C-BED biomarkers are sensitive to norfluoxetine, while revealing pronounced sex-specific differences that underscore their importance for biomonitoring and ecotoxicological risk assessment.