Mercury(Hg) Speciation in different environmental compartments of the India: A Thermo-desorption-Driven Approach

India has a rich environmental ecosystem, stretching from high-rise mountains to coastal areas. The surge in industrialization and economic growth in the country has imposed a considerable burden on the environment, hindering progress toward sustainable development goals. One critical concern in this context is mercury (Hg) pollution, where special attention is needed. On June 18^th 2018, India ratified the Minamata Convention to address Hg pollution. However, a significant data gap exists regarding comprehensive baseline information from different environmental compartments in India, which is crucial for assessing the convention's effects. To bridge this research gap, an effort was made to access Hg distribution and speciation in various environments. For this study, soil and sediments samples were collected from diverse regions: the metropolitan city (Kochi, Kerala, India), agricultural lands (Dhapa, Kolkata), hilly areas (Tea Garden, Darjeeling), and the coastal sediments (collected from continental shelf/slope of the west coast of India). The total soil Hg concentration in metropolitan soil, agricultural soil, and tea garden soil ranged from 16 ± 0.84 µg/kg to 2674 ± 133 µg/kg, 726 ± 36 µg/kg to 2318 ± 115 µg/kg, and 158 ± 7 µg/kg to 9441 ± 472 µg/kg, respectively. Meanwhile, the total Hg concentration in the studied continental shelf sediment samples varied from 8 ± 0.14 µg/kg to 50 ± 2 µg/kg. This result shows that a significantly higher total concentration of Hg in the tea garden soil, whereas lowest Hg concentration were observed in the coastal sediment. Chemical speciation of Hg was carried out using thermo-desorption technique. It was found that the major part of the total Hg was predominantly associated with organic matter in the soil as well as in the coastal sediments. This indicates that organic matter was key host for Hg in soil as well as in coastal sediments. Interestingly, the second-highest fraction in the all types of soil was Hg⁰, indicating more reduction of Hg in the soil. The elevated Hg⁰ levels in the soils raises concerns due to its high volatility at ambient temperatures. The evasion of Hg⁰ from the soil can serve as a significant non-point source of Hg, posing potential risks to individuals living in these areas. Prolonged exposure to this toxic metal could lead to adverse health effects for the local population. Further in the sediments, Hg associated with sulphide was the second dominant Hg fraction, playing crucial role in Hg stability. Overall, these findings not only help to stakeholders and policy makers in addressing Hg pollution, but also contributes to progress towards achieving Sustainable Development Goals.