HEAVY METAL CONTAMINATION AND RISK ASSESSMENT OF WATER, SEDIMENT, AND FARMLAND SOIL AROUND A Pb/Zn MINE AREA IN HUNAN PROVINCE, CHINA

To investigate the influence of heavy metals on water, sediment, and farmland soil around a mining zone, the Panjiachong lead and zinc mining area in Hunan Province was used as the research object, and 30 samples were collected from the river, bottom sediment and soil of nearby farmland in the downstream river area of the Panjiachong tailing darn along the Gantian River. The concentrations of 7 heavy metals, Zn, Pb, Cd, Cr, As, V and Tl, were analyzed. In addition, the heavy metal pollution and risk levels of water, sediment and soil samples were evaluated by the Nemero index, geoaccumulation index and potential ecological risk index. The heavy metal concentrations in 11 water samples were relatively low and were all lower than the limit of the class V water quality standard in the Environmental Quality Standards for Surface Water of China (GB3838-2002). The heavy metal concentrations in sediment and farmland soil samples were relatively high, and the average values of Zn, Pb, Cd and As in 7 sediment samples were 2254, 1720, 2.06 and 259 mg.kg(-1). respectively. The average values of Zn, Pb, Cd and As in 11 farmland soil samples were 688, 510, 2.65 and 87.9 mg.kg(-1), respectively, and the heavy metal concentration gradually decreased with distance from the tailing dam. The three evaluation methods showed that the sediment and farmland soil were at the level of heavy pollution and extremely strong ecological harm, and the order of the ecological risk level of the seven heavy metals was Cd > Pb > As > Zn > Tl > V > Cr. The significant correlation between the heavy metals Zn, Pb, Cd, Cr, V and Tl in sediment and farmland soil samples indicated they originated from the same pollution source.