Trophic transfer of inorganic mercury and methylmercury

Mercury (Hg) is a widespread environmental pollutant with neurotoxic effects. Microorganisms with the hgcA gene can transform inorganic mercury (IHg) into methylmercury (MeHg), which, though present at very low concentrations in seawater (subpicomolar to femtomolar), accumulates in marine food webs, posing risks to marine life and humans. However, the toxic effects of this bioaccumulation have been understudied in natural conditions. Most studies focus on the toxicity of IHg at high concentrations, including oxidative stress, disruption of energy metabolism, and alteration of essential metal homeostasis, but few address MeHg at low marine concentrations. The blue mussel, Mytilus edulis, native to the Atlantic-Channel coasts, has a high capacity to bioaccumulate trace metals in contaminated coastal waters. This study aims to enhance our understanding of the accumulation and effects of different Hg forms (inorganic and organic) in M. edulis, exposed through both water and trophic pathways using enriched stable isotope mixtures, 199IHg and 201MMHg, at realistic (10 pM), moderate (100 pM), and high (1 nM) concentrations over a 96-hour period. For trophic exposure, two types of microalgae (chlorophytes and diatoms) will be cultured under axenic conditions. We will assess the physiological phenotypes of mussels using classical biomarkers of apical effects related to oxidative stress and defense responses at gene and tissue levels combined with high-throughput omics analyses. Additionally, a valvometer will be used to assess bivalve feeding behavior. Finally, to compare the laboratory results, mussels will be caged in different locations in the Channel to determine Hg bioaccumulation and effects in varying environmental conditions and the presence of other contaminants or nutrients in the field.