Mercury Contamination in Aquatic Ecosystems

Mercury contamination in aquatic ecosystems arises from both natural processes and pervasive anthropogenic activities, leading to widespread dispersion of elemental, inorganic and organic mercury species. Atmospheric deposition transports elemental mercury released by combustion and mining into rivers, lakes and coastal waters. In situ microbial transformation, predominantly by anaerobic bacteria in sediments, converts inorganic mercury into methylmercury, the neurotoxic form that readily bioaccumulates in aquatic food webs. Methylmercury burdens top predators and poses severe risks to wildlife and human health via fish consumption. Spatial variability in organic matter composition, redox conditions and biogeochemical cycling governs methylmercury production and bioavailability. While policy measures and emission controls have driven declines in some regions, hotspots persist around industrial zones, artisanal gold-mining sites and in climates altering permafrost and ocean circulation. Understanding the interplay of chemical speciation, sediment inputs and ecological drivers is vital for predicting future risks and guiding remediation efforts under global change.

Research from Nature Portfolio

Recent studies have quantified mercury use in small-scale gold mining, revealing that even with emission-reducing retorts, tonnes of mercury enter river systems annually, fuelling downstream methylation and greenhouse-gas co-emissions. Research on the aquatic continuum has demonstrated that specific thiol functional groups in dissolved organic matter, rather than total organic carbon, control methylmercury speciation and uptake by phytoplankton. Concentrations of these binding sites decline sharply from terrestrial to marine settings, explaining systematic increases in bioavailability across environments. Foundational work has further shown that the molecular origin of sedimentary organic matter—whether plankton-derived or terrigenous—critically shapes in situ methylation rates and the balance between local production and catchment-imported methylmercury in boreal lakes.

Mercury Contamination in Aquatic Ecosystems publication trend

The graph below shows the total number of articles in mercury contamination in aquatic ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Methylmercury (MeHg): The organic, neurotoxic form of mercury produced by microbial methylation in sediments and water, prone to bioaccumulation.

Dissolved organic matter (DOM): A complex mixture of organic compounds in water; DOM‐associated thiol (RSH) groups bind methylmercury and influence its bioavailability.

Bioaccumulation: The process by which organisms absorb and retain contaminants from their environment at levels higher than those in water or sediment.

Biomagnification: The increase in contaminant concentration at successive trophic levels in a food web.

Artisanal and small‐scale gold mining (ASGM): Informal mining practice that uses mercury to extract gold, leading to significant releases into aquatic ecosystems.

Speciation: Distribution of mercury among different chemical forms (e.g., Hg⁰, Hg²⁺, MeHg), which determines its mobility and toxicity.

References

1. Mercury and CO2 emissions from artisanal gold mining in Brazilian Amazon rainforest. Nature Sustainability (2023).
2. Dissolved organic matter thiol concentrations determine methylmercury bioavailability across the terrestrial-marine aquatic continuum. Nature Communications (2023).
3. Molecular composition of organic matter controls methylmercury formation in boreal lakes. Nature Communications (2017).
4. Global mercury emissions to the atmosphere from anthropogenic and natural sources. Atmospheric Chemistry and Physics (2010).
5. A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use. Ambio (2018).
6. Modulators of mercury risk to wildlife and humans in the context of rapid global change. Ambio (2018).
7. Permafrost Stores a Globally Significant Amount of Mercury. Geophysical Research Letters (2018).