Impacts of UV-filter pollution and low pH: Sperm and adult biomarkers in the mussel Mytilus galloprovincialis in a multi-stressor context

In an era of unprecedented environmental changes, understanding the combined effects of multiple stressors on species' performance is urgent. The increasing UV-filter incorporation in daily-life products raises concerns about their potential impact on marine-coastal environments upon release. As stressors rarely act alone, global change-induced factors, such as ocean acidification (OA), can amplify ecological hazards promoted by contaminants in coastal realms. This study investigated the combined impacts of UV-filters 4-methylbenzylidene camphor (4-MBC) and benzophenone-3 (BP-3), at ecologically relevant concentrations (1 and 10 µg/L), under two target pH levels (8.2 and 7.7, reflecting a ∆pH of 0 and -0.3 relative to the average pH at the sampling site), on the biological performance and male reproductive health of the mussel Mytilus galloprovincialis. Using sperm and adult assays alongside a multi-biomarker approach, the study revealed that pH was the primary driver of the decline in mussel physiological and biochemical performances, further intensifying UV-filters' impacts. While sperm cells showed adaptive responses to low pH conditions alone, characterized by reduced lipid peroxidation (LPO) levels and superoxide anion overproduction, adult mussels experienced more pronounced effects, particularly under simultaneous exposure to low pH and UV-filters. Specifically, the adults exhibited distinct bioconcentration patterns under low pH, enhanced cellular metabolic activity and energy-demand compensatory processes, activation of biotransformation pathways, and regulation of antioxidant defenses. Given the ecological and socio-economic importance of M. galloprovincialis and its demonstrated vulnerability to these stressors, these findings highlight the need for further studies on potential transgenerational impacts and evolutionary implications for mussel populations.