The application of preliminary sediment quality criteria to metal contamination in the Le An River

An equilibrium partitioning approach was employed to develop preliminary sediment quality criteria (SQC) for heavy metals in surficial sediments of the Le An River, near the large Dexing copper mine. Acid-volatile sulfide and interstitial water criteria toxic units for single and multiple metals were derived in this study. After comparison, the results indicated that, within different sections of the river, violation of corresponding SQC by current concentrations of copper, lead and zinc occurred to varying extents. This situation is probably attributable to the discharges of acidic drainage carrying a large amount of copper originating from Dexing copper mine, and to wastewaters containing high levels of zinc and lead released from numerous small smelters and panning activities along the banks of the river. The acidity of effluents from mining activities, and the excessive concentrations of multiple metals, particularly copper in the sediments, made dominant contributions to the severe degradation of local benthic ecosystems. These conclusions are in accordance with an assessment made using the integrative sediment quality triad. Based on combined evidence from different approaches, therefore, control at the contaminant sources is urgently required.