Pollution characteristics and probabilistic health risk assessment of potentially toxic elements in surface water from a representative lake in cold-arid regions

As key safeguards of water security in fragile ecosystems, lakes in cold and arid regions are increasingly contaminated by potentially toxic elements (PTEs) from anthropogenic activities. Such contamination threatens water quality, ecosystem stability, and ultimately public health via geochemical cycling. However, the associated health risks and pollution sources have not yet been quantitatively assessed. To assess the pollution status of PTEs in lakes in cold and arid regions over different periods and evaluate the associated health risks for basin populations, 120 surface water samples were collected during ice-free and ice-covered periods in Wuliangsuhai Lake, Inner Mongolia. The concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were measured, and the pollution was evaluated using the Nemerow composite index and Heavy metal pollution index (HPI) methods, while the Positive Matrix Factorization (PMF) model was implemented to trace the pollutant sources and Monte Carlo simulation was adopted to assess the health risks. The results indicated that the overall PTE concentrations in both periods were below the Class III surface water environmental quality standard (GB3838-2002) and farmland irrigation water quality standard (GB5084-2021). The Nemerow index revealed that As, Cd, Cr, Cu, Ni, Pb, and Zn were consistently at clean levels, whereas Hg was clean in 96.67 % of the samples during the ice-free period and was entirely clean during the ice-covered period, making Hg the primary pollutant. Sampling points L11, M14, and Q8 showed slight pollution during the ice-free period but were clean in the ice-covered period, with the overall pollution more severe in the ice-free period. The mean HPI values were 69.30 during the ice-free period and 31.73 during the ice-covered period, both below the acceptable threshold of 100. Attention should be directed toward pollution caused by PTEs at certain sampling points. Source analysis using the PMF model revealed that industrial production, natural factors, mixed sources of transportation and atmospheric deposition, agricultural activities, and mixed sources of human activities and natural factors contributed 22.48 %, 22.01 %, 20.36 %, 17.76 %, and 17.39 % of the PTE pollutants, respectively. Monte Carlo simulations indicated that cancer risk was the main health risk for the population, with the 95 % quantile values of the total cancer risk for adults and children in both periods remaining below the threshold of 1.00E-4, suggesting an acceptable level of risk. Cr has emerged as the most critical environmental factor driving cancer risk, with children being more vulnerable than adults. However, non-cancer health risks for adults and children were negligible during both periods. These results provide valuable data and a theoretical basis for the precise management and mitigation of water pollution in the region.