重金属Cd在再生水—土壤—蔬菜体系中的迁移

Migration of Heavy Metal Cd in Reclaimed Water-Soil-Vegetable System

通过小区试验种植了小白菜和萝卜,以再生水灌溉和污泥施肥,采用修正的BCR法测定了再生水、污泥、土壤、蔬菜中重金属Cd的5种形态含量,分析Cd在再生水(污泥)-土壤-蔬菜体系中的迁移和累积特征。结果表明:灌溉用清水和再生水中Cd的总量均未超出国家农田灌溉水质标准(GB5084-2005)的规定,但水样中的Cd主要以水溶态存在,生物有效性系数K≥0.85。经再生水灌溉和污泥施肥后土壤中Cd的形态和总量均发生了变化。蔬菜地上部分中Cd以水溶态B0和可氧化态B3的形式存在,B0>B3;而地下部分以B0、B2和B3为主,B0<B3。两种蔬菜地上部分B0含量均高于其地下部分的含量。用再生水灌溉和施用污泥的蔬菜比仅用清水灌溉的蔬菜富集系数BCF值更高,生物有效性系数K值也大于仅用清水灌溉的蔬菜,其中小白菜可食用部分K≥0.80。两种蔬菜可食用部分中Cd总含量均未超过国家食品中污染物限量(GB2762-2005)的标准。

Small scale experiments were carried out on pakchoi and radish, which were irrigated with reclaimed water and fertilized with sludge, contents of 5 different chemical speciations of Cd in reclaimed water, sludge, soil, vegetable were detected by using modified BCR method, and the migration and accumulation characters of Cd in reclaimed water-soil-vegetable system were analyzed. The results show： the Cd in irrigation water and reclaimed water do not exceed the National Farmland Irrigation Standard（GB5084-2005）, Cd in water sample basically exists in the form of water-soluble and the bio-availibihy coefficient K 〉/ 0.85. The Cd contents and chemical speeiation in soil are changed after irrigated with reclaimed water or fertilized with sludge. Cd in above-ground portion of vegetables exists in the forms of water-soluble BO and oxidable B3, and B0 〉 B3; while in underground portion, mainly BO, B2 and B3, and B0〈B3. Those two vegetables both contain more B0 in above-ground portion than thai in underground portion. Compared with the vegetables irrigated with clear water, the vegetables irrigated with reclaimed water and fertilized with sludge have the higher accumulation coefficient BCF, and it is same for bio-availability coefficient. For example, the K of eatable part of pakchoi I〉 0.80. The Cd contents in the eatable parts of two vegetables aren＇t beyond the National Limitation of Pollutants in Foods （GB2762-2005）.