Geochemical distribution and speciation of Tl and other trace metals in upper Beijiang River in South China: Approach of in-situ DGT monitoring

Abstract

Mining activities frequently result in severe contamination of river water. This study aimed to better understand the spatial distribution characteristics of Tl and other metals (e.g., Al, Cd, Co, Mn, Ni, Zn, Pb, V, As, Mo, and Sb), and to assess their risks to human health. Surface water samples were collected from the upper Beijiang River (South China) via grab sampling and the diffusive gradients in thin-films (DGT) technique. The concentrations of Tl measured by grab sampling and δ-MnO2-DGT ranged from 0.045 μg L−1 to 0.231 μg L−1 and from 0.056 μg L−1 to 0.131 μg L−1, respectively. Most of the metals monitored were below the threshold levels allowed by the drinking water standard in China, except for As, Sb, and Mn at specific sampling sites. The concentrations of other metals measured by grab sampling were higher than those measured using the DGT technique because of the differences in speciation during these measurements. The hazard quotient (5.43 × 10−4–8.0 × 10−1 for grab sampling and 2.23 × 10−4–2.8 × 10−1 for DGT technique) for the monitored trace metals demonstrated minimal health risk to human beings. The pollution status of these toxic metals in the study area was generally acceptable. As was found to be potentially the most harmful metal in the studied area, with hazard quotients at some sampling sites calculated by grab sampling of >1. It has previously been suggested that As is the most important non-carcinogenic contaminant. The combination of grab sampling and the DGT technique provides a comprehensive understanding of trace metals, especially Tl, in terms of potential bioavailability and ecological assessment.