九龙江流域水稻土重金属赋存形态及污染评价

采用改进的BCR四步提取-电感耦合等离子体质谱法(ICP-MS)分析九龙江流域71个水稻土中12种重金属元素的赋存形态特征,运用风险评价编码法(RAC)、次生相与原生相分布比值法(RSP)和地质积累指数法(Igeo)评价重金属污染特征.结果表明,大部分重金属总量已存在不同程度的富集且不同重金属元素在水稻土中的赋存形态特征差异较大.Cd和Mn主要以F1弱酸溶态存在,平均比例分别为46.2%和35.2%;Fe和Pb主要以F2可还原态存在,平均比例分别为64.5%和41.5%;而V、Cr、Ni、As、Co、Sr、Zn和Cu主要以F4残渣态存在,平均比例分别为79.6%、78.4%、73.1%、67.7%、51.9%、49.7%、45.3%和38.4%.3种污染评价方法分别重点关注弱酸溶态、次生相和重金属总量,均有应用价值,缺点是不够全面.结合3种评价方法能更准确全面评估重金属污染特征.九龙江流域水稻土中Cd为中度~重度污染,Mn和Sr为轻度~重度污染,Zn、Pb、Cu和Co为轻度~中度污染,As和Ni为无污染~中度污染,V、Fe和Cr为无污染~轻度污染.

Assessment of the Speciation and Pollution of Heavy Metals in Paddy Soils from the Jiulong River Basin

Speciation characteristics of twelve heavy metals in 71 paddy soils from the Jiulong River Basin were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and the modified BCR protocol. The risk assessment coding method (RAC), ratio of secondary phase and primary phase (RSP), and geoaccumulation index (I_geo) were applied to evaluate the pollution degree of heavy metals in the area. The results show that most of these elements are abundant in the paddy soils and the speciation characteristics of different heavy metals vary. The elements Cd and Mn mainly exist as acid soluble fractions in the soils, with a mean proportion of 46.2% and 35.2%, respectively; Fe and Pb mainly exist as reducible fractions in the soils, with a mean proportion of 64.5% and 41.5%, respectively; and V, Cr, Ni, As, Co, Sr, Zn, and Cu mainly exist as residual fractions in the soils, with a mean proportion of 79.6%, 78.4%, 73.1%, 67.7%, 51.9%, 49.7%, 45.3%, and 38.4%, respectively. The three pollution assessment methods focus on the acid-soluble phase, secondary phase, and total amount of heavy metals, respectively. All have their own application value and disadvantages of incompletion. The comprehensive analysis of these three pollution assessment methods helps to more accurately and comprehensively assess the pollution characteristics of the heavy metals. The results show that the paddy soils are moderately to severely polluted with Cd; the Mn and Sr pollution is mild to severe; the Zn, Pb, Cu, and Co pollution is mild to moderate; the As and Ni pollution is absent or moderate; and V, Fe, and Cr pollution is non-existent or mild.