Seasonal anti-androgen activity in the brackish Baltic waters in relation to the gene expression profiles of the blue mussel Mytilus trossulus.

Endocrine disruptors (EDs) in aquatic environments pose significant risks to marine organisms, affecting critical physiological processes such as reproduction, metabolism, and stress responses. The Baltic Sea, with its high anthropogenic pressure and unique ecological conditions, is particularly vulnerable to EDs contamination. Our study aimed to evaluate the endocrine-disrupting, metabolism-impairing, and cytotoxic effects of water samples collected seasonally from a sewage treatment plant outlet in the Gulf of Gdańsk (Poland). Simultaneously, the gonadal transcriptome profiles of Mytilus trossulus were analyzed to investigate potential responses at the molecular level. Anti-androgenic activity of water samples, quantified using the XenoScreen YAS assay, was the highest in autumn (36.47 µM flutamide equivalents) and winter (23.57 μM), decreasing in spring (4.48 μM) and summer (0.54 μM). No estrogenic or anti-estrogenic activity was detected in the collected water samples tested with the YES assay and using the cell line BT-474. RNA-sequencing of mussel gonads enabled the identification of seasonal transcriptomic changes linked to gametogenesis, steroid and lipid metabolism, and detoxification processes. Seasonal fluctuations in anti-androgenic activity were observed in water samples, accompanied by distinct shifts in gene expression patterns in mussels. While no acute physiological disturbances were detected, the ongoing anthropogenic impact on the Baltic Sea underscores the need for continued monitoring. The findings highlight the potential for EDs-induced disruptions in marine organisms, emphasizing the importance of mitigating human-caused environmental stressors to protect aquatic biodiversity.