Soil Bioavailability and Native Plant Uptake of Mercury in the Contaminated Sites at Kodaikanal, India

Abstract

This paper presents the evaluation of soil contamination with bioaccumulation and bioavailability of mercury in the surroundings of a former thermometer factory at Kodaikanal in connection with several other soil chemical characteristics. Mercury (Hg), a rare earth element, evolves to be the global concern because of its solubility and its persistence in nature. It is also widely known as a potential neurotoxin since it has the ability to bind with the thiol functional groups in the living system because of the accumulation in food chain and its biomagnifications. The Study was carried out at Department of Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore, India during 2018-2020. Geo-coded soil and plant samples were collected in and around the former thermometer factory in different possible direction. The total mercury content in the soil ranged from 0.19 to 4.7 mg kg-1 and the water soluble mercury fraction ranged from 0.01 to 0.07 mg kg-1 in various sampling sites. The total mercury of the samples ranged from 0.24 to 3.80, 0.84 to 1.55, 0.45 to 1.67 and 0.19 to 4.97 mg kg-1 in east, north, south and west directions, respectively whereas the water soluble mercury fraction ranged from 0.01 to 0.07 and 0.01 to 0.04 mg kg-1 in east and west direction, respectively corresponding to 0.5 to 5.36 % of the total. Despite this analysis, other chemical parameters were also studied to determine their extent of influence on mercury accumulation and availability. Among those parameters, pH was found to be having significant correlation with total mercury and water soluble mercury. The concentration of total mercury and water soluble mercury recorded were less than the permissible limit set by International standards (Canadian Soil Quality Guidelines). Among different plant species, Roots of Sterculia sp. was found to accumulate 1.19 mg kg-1 whereas mercury content was found to be below detectable limits in other plants. Based on the results obtained from Potential Ecological Risk Index, it was concluded that risk associated with soil mercury contamination is low in the study area at Kodaikanal.