套种条件下混合螯合剂对污染土壤Cd淋滤行为的影响

为了研究螯合剂对污染土壤Cd向下迁移的影响,对采自广东省乐昌市和清远市的2种铅锌矿废水污染水稻土（分别为中性和酸性土壤）进行100 cm土柱室外淋溶试验,研究在玉米与东南景天套种系统中,在5 mmol.kg-1土的混合螯合剂MC∶柠檬酸∶味精废液∶EDTA∶KCl（摩尔比）=10∶1∶2∶3]的强化作用下对2种污染土壤中Cd的淋滤行为的影响.结果表明,施加混合螯合剂后第2 d,混合螯合剂能明显提高2种土壤各土层淋滤液Cd浓度;施后第8 d混合螯合剂仍能继续提高中性土壤20 cm以下土层和酸性土壤60 cm以下土层淋滤液Cd的浓度,但其活化作用均已迅速下降.施后第2 d和第8 d,2种土壤各土层的套种＋MC处理的淋滤液Cd浓度均超过国家地下水质量标准（GB/T 14848-93）.施加混合螯合剂可降低中性土壤表层全Cd量.不同处理的土壤Cd均有向下层迁移的趋势,尤其是酸性土壤,在20 cm和40 cm处不同处理的全Cd量与起始值比较分别下降了40%～58%和39%～49%,经过100 d的修复即可达到土壤环境质量标准（GB 15618-1995）.上述结果表明,施用混合螯合剂对Cd污染土壤的地下水水质存在一定的潜在污染风险.

Effects of Mixed Chelators on the Leaching of Cadmium in Contaminated Soils Under Intercropping System

In order to elucidate the influence of chelators on Cd leaching in contaminated soil, outdoor soil column (100 cm) leaching experiments were conducted using two paddy soils irrigated with Pb-Zn mining wastewater. Soil samples which under intercropping systems were collected from Qingyuan City (acid soil with pH 4.63) and Lechang city (neutral soil with pH 6.51), Guangdong Province of China. The mixture of chelators (MC) comprised of citric acid, monosodium glutamate waste liquid, EDTA and KCl with molar ratio of 10 : 1 : 2 : 3 at the concentration of 5 mmol x kg(-1) soil. The intercropping system used in this study was a Zn- and Cd-hyperaccumulator (Sedum alfredii) and a low-accumulating crop (Zea mays). Results showed that at day 2 after the application of MC, the Cd concentrations in leachates from every layer of neutral and acid soils increased significantly in the treatment with intercropping and MC. At day 8 the concentrations of Cd in leachate from layers below 20 cm in the neutral soil and below 60 cm in the acid soil were still significantly higher than those of control. However, the mobility of Cd was decreased greatly compared with that at day 2. At day 2 and day 8 the Cd concentrations in leachates from every layer of neutral and acid soils in the Co-crop + MC treatments exceed the value of the Groundwater Quality Standards (GB/T 14848-93). Cd in all soil columns showed the trend to migrate downwards, especially in the acid soil. The total Cd in the soil layers of 20 cm and 40 cm was decreased by 40% -58% and 39%-49% respectively at the end of the experiments compared to the initial value. After leaching of 100 days,the total Cd in 0-40 cm soil layer of acid soil reached the limit of National Soil Environmental Quality Standards (GB 15618-1995). The results also implied that in Cd-contaminated soil MC addition might enhance the potential risks of Cd contamination in groundwater.