废弃砷矿区周边生态系统的重金属分布特征及污染评价

Distribution and Evaluation of Heavy Metal Pollution of the Reservoir near an Abandoned Arsenic Mine

研究废弃砷矿影响下水库及周边生态系统中重金属分布特征和生物污染状况,可为土壤和水生态修复及治理提供参考数据。2019年夏季采集了粤北某水库的动物、植物和水样,测定了砷(As)、镉(Cd)、铅(Pb)、铬(Cr)、汞(Hg)共5种重金属含量,采用单因子污染指数法和均方根综合指数法进行污染评价。结果显示,水中重金属含量沿矿口到水库一线下降明显,As含量最高,为0.0980~1.0010 mg/L;农作物中,重金属综合污染指数由高到低依次为:As>Cr>Pb>Hg=Cd,As污染程度从大到小依次为:白菜(中度污染)>花生(中度污染)>番薯(中度污染)>南瓜(轻度污染);乡土植物中,凤尾蕨对As富集效果明显,平均含量达1286.4234 mg/kg;5种重金属在水生生物中综合污染指数由高到低依次为:As>Pb>Cd>Cr>Hg,3种水生生物重金属综合污染指数由高到低为:河蚌(轻度污染)>太阳鱼(轻度污染)>鲤(轻度污染)。研究表明,受粤北地区重金属高背景值和砷矿的影响,水库生态系统已存在轻微的生态风险,植物和动物处于轻度污染状态,矿口周边的植物污染程度较严重,应引起足够重视。

In this study, we explored the heavy metal distribution and pollution status of a reservoir near an abandoned arsenic mine in Guangdong Province, China. The aim was to provide a reference and data base for evaluating heavy metal pollution and treatment of the ecosystem around the mining area in northern Guangdong Province. The reservoir in this study, located north of Shaoguan City, is connected to the old arsenic mine site by a small stream. Eight sampling sites were set in and near the reservoir: five in the reservoir and one each at the reservoir inlet, the ecological restoration zone and the old mine site. In the summer of 2019, samples of water, plants and aquatic animals were collected and analyzed for heavy metals,including: arsenic(As), cadmium(Cd), lead(Pb), chromium(Cr) and mercury(Hg). The plants sampled included crop and native plants, and the animals sampled included freshwater mussels, sunfish and carps.Heavy metals were determined by ICP-MS, and the heavy metal pollution status of the area was evaluated by the single factor pollution index and the comprehensive pollution index. Heavy metal concentrations in the water decreased significantly from the mine site to the reservoir inlet, and the concentration of As was the highest(0.0980-1.0010 mg/L). Across the five reservoir sampling sites, the heavy metal concentration ranges for As, Cd, Pb, Cr and Hg were, respectively, 0.096-0.104 mg/L, ND-0.0045 mg/L, ND-0.0063 mg/L, 0.0048-0.0064 mg/L and ND-0.0051 mg/L(ND, not detected). The As concentration approached surface water standard IV, indicating a serious As pollution risk. In crop samples, the concentrations of the five heavy metals were in the order As>Cr>Pb>Hg-Cd. The As content of crop plants followed the order, cabbage>peanut>sweet potato>pumpkin. Among the native plants, the As content of ferns was clearly elevated, with an average concentration of 1 286.4 mg/kg. The concentration ranges of As, Cd, Pb,Cr and Hg in the muscle tissue of the three aquatic animals were, respectively, 0.2707-1.5341 mg/kg,0.0018-0.1307 mg/kg, 0.0075-0.3972 mg/kg, 0.0935-0.1986 mg/kg and 0.0087-0.0132 mg/kg. The relative comprehensive pollution index for the heavy metals was, in order, As>Pb>Cd>Cr>Hg and, for the three aquatic animals, the order was freshwater mussels>sunfish>carps. In general, the elevated heavy metal levels resulting from mining activities in Guangdong Province pose a slight ecological risk within the reservoir. Plants and animals in the area are classified as lightly polluted, except for plants near the mine entrance, which are seriously polluted. The single factor pollution index of As in the study area was higher than in other regions of China, indicating that the arsenic mine did pollute local soils and plants.Therefore, trees and grass should be planted to increase filtration capacity and reduce heavy metal inputs to the reservoir.