西安市郊不同年限设施菜地土壤Cd和Pb形态分析与污染评价

Speciation and pollution assessment of cadmium and lead in vegetable greenhouse soil from a Xi′an Suburb with different cultivating years

为探究不同种植年限设施菜地土壤重金属的形态与污染程度变化,以西安市郊不同年限设施菜地土壤为研究对象,通过测定不同年限土壤理化性质和重金属含量,利用BCR连续提取法研究土壤中Cd和Pb的不同形态,分析土壤中Cd和Pb不同赋存形态与土壤理化性质之间的关系,并采用地积累指数法和潜在生态风险指数法对设施菜地重金属污染进行风险评价。结果表明:随着种植年限增加,西安市设施菜地土壤呈酸化趋势,且速效养分含量升高;不同年限设施菜地土壤重金属Cd和Pb的总量分别为0.28~1.51 mg·kg^(-1)和0.14~0.5 mg·kg^(-1),Cd有效态含量介于0.14~0.5 mg·kg^(-1),均超过其地方土壤背景值,大棚使用年限为11~15、16~20、21~25 a中Cd总量分别为0.615、1.465、1.515 mg·kg^(-1),在21~25 a中Cd有效态含量为0.5 mg·kg^(-1),均超出标准限值;弱酸态和还原态是大棚土壤中Cd的主要存在形态,而Pb主要存在形态为残渣态。其中土壤中Cd的有效态、Pb的还原态和残渣态与土壤N、P含量显著相关(P<0.05),Pb的还原态与K含量相关。随着年限增长,设施菜地土壤中Cd的地积累指数增加,污染程度达到中度污染。研究区21~25 a设施菜地为中等生态风险,Cd生态风险系数对潜在风险指数的贡献高达94.36%,重金属Cd和Pb存在一定的累积叠加污染风险。高年限设施菜地土壤Cd的潜在生态风险系数大于Pb。

The physioehemieal properties, content and speeiation of heavy metals changes the increasing planting years. To investigate the speeiation and pollution levels of heavy metals in vegetable greenhouse soils with different planting years, a field study was conducted using vegetable greenhouse soil from a Xi ＇ an Suburb. The physioehemieal properties, content, and speeiation of Cd and Pb in soil were investigated, the relationship between Cd and Pb speeiation and their physioehemieal properties in soil were analyzed, and heavy metal pollution in soil was evaluated using the geoaeeumlation and potential ecological risk indices. The results indicated that soil became acidic and the availability of nutrients increased an increase in planting years. The total Cd and Pb content of soil ranged between 0.28～1.51 mg· kg-1 and 0.14- 0.5 mg· kg-1, respectively, and the available content of Cd was between 0.14-0.5 mg. kg 1; all of these values exceeded the background level. The total contents of Cd in 11-15, 16-20 a and 21-25 a were 0.615, 1.465 mg. kg 1, and 1.515 mg· kg-1, respectively, and that of 21-25 a were 0,5 mg·kg-1, which exceeded the standard value. The acid soluble and reducible fraetions were the main speeiations of Cd. The main form of Pb was the residual fraetion. The available Cd, and the reduction and residue fraetions of Pb were significantly correlated with the N and P contents of soil（P〈0.05）, and the reduction fraction of Pb was correlated with K. The geoaccumulation index of Cd in soil increased, and the pollution reached a moderate level as the number of planting years increased. The soil of 21-25 a was at a moderate ecological risk. The contribution of the Cd ecological risk coefficient to the potential risk index was 94.36%. Cd and Pb create a certain risk of superimposed pollution, and the potential ecological risk coefficient of Cd in high-age fields is greater than that of Pb.