Distribution and assessment of Pb in the supergene environment of the Huainan Coal Mining Area, Anhui, China

Coal mining area is highly subject to lead (Pb) pollution from coal mining activities. Several decades of coal mining and processing practices in dozens of coal mines in the Huainan Coal Mining Area (HCMA) have led to the accumulation of massive amounts of coal gangue, which piled in dumps. In order to investigate the impacts of coal gangue dumps on Pb level in the supergene media of the HCMA, a systematic sampling campaign comprising coal gangue, soil, wheat, and earthworm samples was conducted. The average Pb content in the coal mining area soil is 24 mg/kg, which is slightly higher than the associated coal gangues (23 mg/kg) and markedly higher than reference region soil (12.6 mg/kg). Soil in the HCMA present a slight to moderate Pb contamination, which might be related to the weathering and leaching of coal gangue dumps. Lateral distribution of Pb in HCMA soil differed among individual coal mines. The soil profile distribution of Pb depends on both natural and anthropogenic contributions. Average Pb content is higher in roots than in stems, leaves, and wheat husks, while the Pb level in seeds exceeded the maximum Pb allowance for foods (Maximum Levels of Contaminants in Foods of China, GB 2762-2012). Earthworms in the selected area are significantly enriched in Pb, suggesting higher bio-available Pb level in soil in the HCMA.