Speciation-Driven Toxicity and Remediation of Mercury: Mechanistic Insights and Policy Implications

Mercury is a worldwide spread pollutant whose effects are more related to chemical speciation rather than concentration. Changes between elemental mercury (Hg 0 ), inorganic mercury (Hg 2+ ) and organomercury species, including methylmercury (CH 3 Hg + ), Dimethyl mercury (CH 3 ) 2 Hg + ) and ethylmercury (EtHg), determine the mobility, bioavailability, and toxicity of mercury in soil, water, sludge, and air. These dynamic changes are caused by factors such as pH, redox potential, organic matter and microbial activity. Elemental mercury (Hg 0 ) causes inhalation toxicity, considered relatively less toxic but can be oxidized to inorganic mercury (Hg 2+ ), which has higher affinity for sulfhydryl groups in protein and enzymes, leading to cellular dysfunction and kidney damage. The most hazardous form is organic mercury, particularly methylmercury which easily crosses biological membranes, including the blood brain and placental barrier. Once inside the body, methyl mercury bind to thiol containing molecules contains molecules, cause sever disproportionate neurodevelopmental damage by food webs. Dimethyl mercury is even more toxic, penetrate skin and tissue rapidly, resulting in acute poisoning at extremely low exposure level. Mercury speciation has a significant impact on plant uptake, cross-species toxicity and remediation. The risks can be alleviated by phytoremediation, microbial transformation, sludge treatment, and thermal or chemical stabilization, and mitigated or inadvertently increased by specification-conscientious planning. Detection is improved by the development of analytical methods, such as HPLC-ICP-MS, CVAFS, X-ray absorption spectroscopy, and biosensors, but in situ and real time monitoring is still problematic. Speciation metrics should replace bulk mercury levels, which should be incorporated in policy systems, including the Minamata Convention. In the future, the integration of mechanistic models and field data, the creation of AI-based speciation prediction, and the implementation of low-cost biosensors are important, especially in poorly-infrastructure-equipped regions. Sustainable mercury management should be based not only on reduction of the total amount but also on conversion of mercury into less toxic and mobile states.