Hydrogeochemistry of groundwater surrounding a pyrite mine in southern China: Assessment of the diffusive gradients in thin films technique for in situ monitoring

Abstract

Acid mine drainage (AMD) resulting from pyrite mining causes hydrogeochemical evolution of groundwater and, in particular, the consequent release of potentially toxic elements (PTEs), posing health risks to populations dependent on groundwater. In this study, hydrogeochemical characteristics and evolutionary mechanisms were systematically illustrated via multivariate statistical methods and hydrogeochemical methods based on groundwater samples (n = 40) collected in a pyrite mining area in southern China. The diffusive gradients in thin films (DGT) technique was applied to evaluate the accuracy of metal content detection in groundwater at low concentrations. Based on principal component analysis (PCA), the groundwater dataset was classified into four types: brackish water dominated by sulfate, brackish water dominated by Ca-HCO3, low-mineralized water with the presence of PTEs, and freshwater in its natural state. The main controlling factors of hydrogeochemistry are evaporative crystallization and water–rock interactions. Fe, Mn, Pb, and Cd were detected in groundwater in the study area at levels exceeding World Health Organization (WHO) parameter values, and the highly toxic trace metal Tl was detected at levels up to 20 μg/L. The assessment of the applicability of the DGT technique to groundwater systems showed that reliable DGT detection results could be obtained under neutral or alkaline conditions at low Mn and Cd levels. This study highlights the evolution of the groundwater hydrogeochemistry under the combined influences of human activities such as mining and remediation management. In particular, the release of PTEs can affect human health, while the adoption of in situ DGT technology can provide strong support for studying these issues.