Mercury systematics in aquaculture: Accumulation and transformation

The rapid expansion of global aquaculture, which is now a major source of aquatic products comparable to capture fisheries, is accompanied by significant environmental challenges. Among these challenges, mercury (Hg) and its neurotoxic form, methylmercury (MeHg), present serious threats to product safety and human health, necessitating urgent intervention. This review systematically synthesizes the current knowledge of Hg dynamics in aquaculture systems, which involve diverse exogenous and endogenous inputs, as well as complex multimedia/interface transfers and transformations. We detail Hg accumulation in water, sediments, and farmed organisms and elaborate on key processes such as adsorption–desorption, reduction, and competing methylation and demethylation pathways. A central focus is elucidating the mechanisms governing net MeHg production, encompassing abiotic pathways mediated by organic matter and antibiotics, microbial methylation/demethylation, and the roles of benthic organisms. Our synthesis highlights the pivotal yet dual roles of organic matter in regulating Hg (bio)availability and microbial activity. Its interplay with antibiotics and benthic bioturbation ultimately dictates the net MeHg outcome. Finally, we identify critical knowledge gaps and propose future research priorities, including synchronized and species-specific monitoring, advanced source-apportionment models, and mechanistic studies that integrate molecular-scale characterization of aquaculture-derived organic matter with the impacts of antibiotics and benthic communities. By providing a mechanistic framework for assessing MeHg risks, this review aims to guide actionable strategies and support the sustainable development of this vital food sector.