射阳河流域稻田土耕作层金属赋存形态及生态风险评价

Speciation and Ecological Risk Assessment of Metal Elements in the Paddy Soil of Sheyang River Watershed

摘要: 为研究江苏东部里下河地区稻田土金属累积特征与生态风险水平，调查了该地区最大天然干河–射阳河流域25个稻田耕作层土壤样品的Cu、Zn、Mn、Fe、Mg、Pb、Cr、Ni总量、赋存形态、pH、Eh、EC及TN、TP、TOC含量。采用主成分分析法判断其主要来源，运用地积累指数法(Igeo)、富集因子法(EF)、改进的潜在生态风险指数法(MRI)进行综合的生态风险评价。结果表明：Mg、Zn、Ni、Cu的平均含量分别为12597.20 mg/kg、1557.54 mg/kg、73.71 mg/kg、58.75 mg/kg，均高于环境背景值，其中，Zn、Ni、Cu含量分别达国家二级标准的5.19、1.23、2.63倍；金属Fe、Mn平均含量为22825.12 mg/kg、487.02 mg/kg，均低于环境背景值；金属Pb、Cr含量较低，在30.72~121.61 μg/kg之间，低于国家二级标准。三种方法评价结果均显示，研究区域土壤耕作层中，金属Zn达到中度至重度污染，Ni、Cu为轻度至中度污染，Mn、Fe、Pb、Cr无污染；富集因子计算结果显示Mg达到中度污染。主成分分析显示Zn、Ni同源性较高，可能源于公路交通污染。结合金属有效态占总量比例，改进的生态风险评价显示Zn未达到重度污染水平，在一定程度上提高了评价的准确性。金属污染的来源、影响累积的环境因子，有待开展更加广泛的调查和分析。

Abstract: To determine the metal accumulation characteristics and assess the ecological risks in the paddy soils in Lixiahe Area, eight metal elements (Cu, Zn, Mn, Fe, Mg, Pb, Cr, Ni) and the related physio-chemical parameters were analyzed along Sheyang River, eastern area of Jiangsu, China. Paddy soils samples (0~20 cm) from twenty five sites were analyzed for pH, Eh, EC, contents of metal elements, their fractions, and nutrients (total nitrogen, total phosphorus, total organic carbon). Geoaccumulation index (Igeo), enrichment factor method (EF) and modified potential ecological risk index (MRI) were used to evaluate the pollution condition. Principal component analysis was applied for identifying the sources of metals. The results showed that the average contents of Mg, Zn, Ni and Cu were 12597.20 mg/kg, 1557.54 mg/kg, 73.71 mg/kg and 58.75 mg/kg, respectively, which were higher than environmental background values. The contents of Zn, Ni and Cu were 5.19, 1.23 and 2.63 folds to the national secondary standard. The average contents of Fe and Mn were 22825.12 mg/kg and 487.02 mg/kg, both lower than the environmental background values. The range of Pb and Cr were 30.72~121.61 μg/kg, lower than the national secondary standard. Three assessment models showed that all sites were severely polluted by Zn and significantly moderately polluted by Ni and Cu. Mn, Fe, Pb and Cr almost showed no pollution, while enrichment factor indicated moder-ate contamination of Mg. Principal component analysis showed that Zn and Ni may both come from road traffic source. Modified ecological risk assessment showed that Zn did not reach the serious pollution level thanks to low bioavailable proportion, which improved the accuracy of the evaluation to certain extent. The accurate source of metal pollutants and environmental factors accelerat-ing metal accumulation in Sheyang River catchment require further extensive investigation and monitoring.