Thallium distribution characteristics and pollution evaluation in key river basins in Longnan

The research is to determine the spatial distribution characteristics and pollution status of thallium(Tl) around tailings ponds in key basins of Longnan, and evaluate Tl ecological risk. Analyze and evaluate Tl in various receptors using multivariate statistical methods, single factor evaluation methods, geo-accumulation index method, and health risk assessment methods. The average Tl content in surface water is 0.027 μg·L−1 and in groundwater is 0.043 μg·L−1. The single factor pollution index shows that 96.67% of surface water and 100% of groundwater sites are in a clean state of Tl, with some sites significantly affected by human activities. The average Tl content is 0.200 mg·kg−1 in the topsoil, 0.148 mg·kg−1 in the middle soil layer, and 0.088 mg·kg−1 in the deep soil layer, with some sites exceeding the background value of Gansu Province. The geo-accumulation index method indicates that 97.37% of the surface soil sites are not polluted, and 2.63% are mildly polluted. The health risk assessment shows that the non-carcinogenic risk HQ index of Tl in the topsoil is less than 1 for both adults and children, indicating a low non-carcinogenic health risk. There is a significant spatial distribution difference of Tl in the study area, with the surrounding receptors of 17 tailings ponds not being significantly affected by Tl pollution, resulting in low environmental and health risks.