The alleviating effect and mechanism of selenium on mercury toxicity in a marine copepod

Mercury (Hg) pollution poses a persistent risk to marine ecosystems, yet the influence of trace element interaction on its toxicity remains poorly understood. This study investigated the effects of Hg and selenium (Se) co-exposure on the marine copepod Tigriopus japonicus, focusing on reproductive performance, Hg bioaccumulation, and the underlying molecular responses. Hg exposure alone significantly increased Hg accumulation and reduced fecundity. In contrast, HgSe co-exposure decreased Hg accumulation and partially restored reproductive output, providing clear evidence of their antagonistic interaction. Transcriptomic analyses revealed that Hg disrupted metabolic and lipid homeostasis, and promoted oxidative stress, lysosomal dysfunction, and apoptosis, while suppressing vitellogenin expression. Co-exposure with Se counteracted these effects by enhancing energy production via glycolysis and activating antioxidant and glutathione S-transferase-mediated detoxification pathways, thereby stabilizing cellular function and restoring reproductive investment. Collectively, our findings demonstrate a clear antagonistic interaction between Se and Hg in which Se mitigates Hg toxicity through a dual mechanism: reducing Hg bioavailability and reinforcing cellular defense and energy supply systems. This study provides mechanistic insights into SeHg antagonism in marine copepods and highlights the importance of incorporating trace element interactions into ecological risk assessments for Hg pollution in coastal ecosystems.