Water quality analysis and groundwater health risk assessment of acid mine inflow from abandoned coal mines around Guangyuan City

The abandoned coal mines around Guangyuan City were taken as the study area to reveal the impact of acid mine wastewater on the water quality composition of its surrounding groundwater and surface water, as well as the potential hazard of metal element in the groundwater to human health, The conventional index and metal elements in 23 groundwater samples and 39 surface water samples in the target region were determined and analyzed. The environmental quality of groundwater and surface water in the study area was analyzed on the basis of the Nemero comprehensive index method and the pollution index method, and the health risk assessment model was applied to evaluate the health risk of groundwater in the study area. The research showed that the groundwater within the study area contained a high level of total dissolved solids (TDS), SO₄ ²⁻, Ca²⁺ and Mg²⁺ with the highest average mass concentration of TDS and SO₄ ²⁻, which exceeded Class Ⅲ limits in Environmental Quality Standards for Surface Water (GB 3838-2002). In addition, high levels of TDS, SO₄ ²⁻, Ca²⁺ and Mg²⁺ caused poor groundwater quality. Among the above elements, SO₄ ²⁻and TDS had the highest average mass concentrations. The average concentrations of heavy metals in the studied groundwater were in the following order: TFe (sum of Fe²⁺and Fe³⁺) > Al³⁺>Pb²⁺>Zn²⁺>Mn²⁺>Cu²⁺>TCr (sum of Cr³⁺ and Cr⁶⁺)>Cd²⁺>As>Hg, with nine heavy metals exceeding Class Ⅲ limits in Standard for Groundwater Quality (GB/T 14848-2017). According to the results, the eastern region had more metal element in its groundwater than the west; and the groundwater quality in Wangcang County was the most seriously polluted by heavy metals. According to the Nemero index evaluation, most surface water evaluation results were good or excellent, and a few were poor or very poor. This was in good agreement with the pollution index evaluation results, which indicated that the pollution was mainly caused by the discharge of mine water inflow. According to the health risk evaluation results, the groundwater in the study area had a high health risk. The main carcinogenic elements were As, Cd and Cr. The carcinogenic risk of these three elements was all above the maximum risk limit of 10⁻⁴. Meanwhile, the total non-carcinogenic risk of the groundwater exceeded 1 (the acceptable health risk limit), indicating a serious risk of non-carcinogenic disease. The potential non-carcinogenic risk from oral exposure to groundwater in the survey area exceeded that of skin exposure, and the adults bore higher potential non-carcinogenic risk than minors. The results of this study indicated that the quality of groundwater within the study area posed a great threat to people’s health, and the groundwater in the study area was not suitable for drinking. As for the future use of the water bodies, more significance should be attached to the prevention and control of risk from the heavy metals Al, Pb, Zn and Fe.