Ecotoxicity of the non-dioxin-like PCB-153 in the model marine diatom Phaeodactylum tricornutum

Despite the ban on polychlorinated biphenyls (PCBs) in developed countries since the 1930s, their persistence and use endured in developing countries, with reported toxic effects on various organisms. PCB congener 153 (PCB-153, 2, 2 ', 4, 4 ', 5, 5 '-hexachlorobiphenyl) is notably prevalent in marine biota. However, its mode of action and impact on primary marine diatoms are not well documented. Phaeodactylum tricornutum cultures exposed to environmentally relevant PCB-153 levels (0, 1, 3, and 6 mu g/L) showed proportional accumulation, impairing photochemical processes by directly affecting the structure and function of Photosystem II and hindering light harvesting and electron conversion. This impairment significantly inhibited growth (calculated IC25 = 3.53; predicted IC50 = 7.09 mu g/L) within environmental concentrations, which is linked to oxidative stress despite antioxidant responses and increased fucoxanthin production. The increased pheophytin a levels along the PCB153 gradient further supported this finding. Key biomarkers identified with a direct correlation with the exposed and internalized PCB doses included pheophytin a, fucoxanthin, catalase activity, non-photochemical reaction index (SFI [NPQ]), and growth inhibition. PSII functioning parameters (ABS/CS, ET/CS, TR/CS, SM, and Mo), photochemical reaction index (SFI), and specific growth rate showed strong inverse correlations with the PCB153 dose. This study provides new insights into PCB-153 ecotoxicity in marine phytoplankton and highlights effective biomarkers for future ecotoxicological assessments of marine diatoms.