Using Caenorhabditis elegans to assess the ecological health risks of heavy metals in soil and sediments around Dabaoshan Mine, China

Heavy metal pollution is a global environmental problem, and the potential risks associated with heavy metals are increasing. The acid mine drainage (AMD) which is generated by mining activities at Dabaoshan Mine, the largest polymetallic mine in southern China, is harmful to local residents. A detailed regional survey of the ecological and human health risks of this polluted area is urgently needed. In this study, eight sediments and farmland samples were collected along the flow direction of tailing wastewater and Fandong Reservoir; the content of multiple heavy metals in these samples was determined by inductively coupled plasma mass spectrometry. The biological toxicity of water-soluble extracts from the samples was further assessed by referring to different endpoints of Caenorhabditis elegans (C. elegans). The relationship between specific heavy metals and biological toxicity was estimated by partial least squares regression. The results indicated that the risk of heavy metals in Dabaoshan mining area was very high (potential ecological risk index = 721.53) and was related to geographical location. In these samples, the carcinogenic risk (the probability that people are induced carcinogenic diseases or injuries when exposed to carcinogenic pollutants) of arsenic (As) for adults exceeded the standard value 1 × 10⁻⁴ and indicated that As presented a high carcinogenic risk to adults, while the high risk of non-carcinogenic effects (the hazard degree of human exposure to non-carcinogenic pollutants) in children was related to lead exposure (hazard index = 1.24). In addition, the heavy metals at high concentration in the water-soluble fraction of sediment and farmland soil extracts, which might easily distribute within the water cycle, inhibited the survival rate and growth of C. elegans. Gene expression and enzymatic activity related to oxidative stress were increased and genes related to apoptosis and metallothionein were also affected. In conclusion, the results of chemical analysis and biological assays provided evidence on the toxicity of soil and sediment extracts in the Dabaoshan mining area and advocated the control and remediation of heavy metal pollution around Dabaoshan Mine.