Heavy metal pollution in a black shale post-mining site of southern China: Pollution pattern, source apportionment and health risk assessment

Source apportionment is critical but remains largely unknown for heavy metals in the soil surrounding black shale mining areas. Herein, the distribution, potential hazards, and sources of heavy metals in the soil around a black shale post-mining site were investigated. The content of Cadmium (Cd) in topsoil samples (0.77-50.29 mg/kg, N = 84) all exceeded the Chinese agricultural soil standard (0.3 mg/kg). The majority of Cd in the soil existed in the mobile fraction posing a high potential risk to the local ecosystem. and Zn and V in soils existed in the residual form. The percentages of HQing > 1 and 0.6-1 for Vanadium (V) in soil were 8.3% and 31.0%, respectively, and the percentages of HQing > 0.5 for Cd in soil were 3.7% showed that V and Cd were the main factors that increased the potential non-cancer risk. Five potential sources were identified using the geostatistical and positive matrix factorization (PMF) model, among which Cd was mainly derived from the short-term weathering process of black shale (81.06%), most Zinc (Zn) was from the long-term weathering of black shale (67.35%), whereas V was contributed by many factors including long-term weathering of black shale (42.99%), traffic emissions (31.12%) and agricultural activities (21.05%). This study reveals the potential risk and identifies the sources of heavy metals, which is helpful to manage the contaminated soil in black shale mining areas.