Surficial sediments and water (27 samples each) were collected from three representative lakes collapsed by mining activities in Huaibei, China. Contents of heavy metals (Sb, As, Cd, Pb, Zn) in both water and sediments were detected via atomic absorption spectrophotometry and atomic fluorescence spectrometry, respectively. The variation coefficient (C.V.) of each heavy metal as well as the partition coefficient (Kd) between surficial sediments and water was calculated. The ecological risks of heavy metals in collapsed lakes were assessed via geoaccumulation index (I geo), and we estimated the Pearson correlation coefficients between heavy metals. Together with the real situations around collapsed lakes, we resolved the sources of heavy metals. We found that the contents of heavy metals in water were basically below Surface Water Quality Standard I. The contents of heavy metals in the majority of sediment samples exceeded the background levels in the Yangtze River and Huai River areas, but were below the threshold effect concentration. The spatial distributions of heavy metals in surficial sediments were not uniform, as the C.V.s indicate medium variations. Analysis of Partition coefficient showed that Lieshan collapsed lake (LSH) was under severe risk. An analysis of I geo revealed gentle-medium ecological risks from Sb, As, and Cd. The classification and frequency distributions of I geo of five heavy metals indicate that the ecological risk of Cd was the largest. The ecological risk was lowest in Yangzhuang collapsed lake (YZH). These results were confirmed by analysis of C.V. and Kd. Analysis of heavy metal sources showed that the inputs of Sb and As into the three collapsed lakes were human-driven and very complex, probably due to point-source pollution, including leaching from gangue piles and industrial discharge. Cd mainly originated from non-point-source agricultural pollution, while Pb and Zn might mainly originate from natural sources.
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