宜兴地区水稻土Pb Cd Cu Zn污染及垂直分布特性研究

Pollution and Vertical Distribution of Pb,Cd,Cu & Zn in Paddy Soils in Yixing

通过测定宜兴地区34个采样点水稻糙米和不同土层(0～20、20～40、40～60和60～80cm)中Pb、Cd、Cu和Zn含量,利用单项污染指数法和内梅罗污染指数法对土壤表层和糙米重金属含量进行评价,同时分析4种重金属在土壤剖面中的分布规律以及在糙米中的富集特性。结果表明,水稻土表层Pb、Cd、Cu和Zn的平均含量都处于未污染水平,综合评价结果属于清洁(安全)等级;糙米Pb、Cd、Cu和Zn的平均含量也都处在未污染水平,综合评价结果也属清洁(安全)等级。水稻土Pb和Cd的剖面分布属于表层富集型,表层主要受人类活动的影响,而下层跟母质有关;Cu和Zn的剖面分布同属均匀分布型,表层含量略高与人为因素有关,20～40cm和40～60cm含量略低,可能是因为水稻的吸收作用,60～80cm含量比上层都稍高,主要是受成土母质的影响。糙米中4种元素的富集能力存在极显著差异,其大小顺序为Zn(0.282)>Cd(0.234)>Cu(0.198)>Pb(0.014);糙米Pb、Cd、Cu和Zn的含量与土壤表层相应元素的全量具有极显著的正相关关系,相关系数分别达到0.905、0.925、0.939和0.957;糙米中Cd与Cd/Zn比具有极显著的正相关关系(0.837),糙米Cd/Zn比为0.002,远低于临界值0.015。

The contents of Pb, Cd, Cu and Zn in different layers of paddy soil（0-20, 20-40, 40-60 ＆ 60-80 cm ） and in brown rice from 34 sampling sites in Yixing were measured and then assessed by the single pollution index and Nemerow pollution index. Four elements＇ distribution in soil profiles and accumulation in brown rice were also analyzed. Results showed that none of the four elements reached pollution level in the surface soil, and the Nemerow pollution index indicated that the paddy soils in Yixing were clean（ safe ）. The four metals in the brown rice were all below the standard and their assessment showed that the brown rice in Yixing was clean（ safe ） too. The distribution of Pb and Cd in the soil profiles showed the surface layer accumulation, which was caused by anthropogenic activities. Both Cu and Zn distributed uniformly in the four layers. The contents of these two elements in surface soil were slightly higher, which was mainly related to human factors. Their contents in 20-40 and 40-60 cm were slightly lower; maybe a result of the uptake by rice. Due to the effect of parent material, Cu and Zn were slightly higher in 60-80 cm than other layers. The bioconcentration factors of the four metals differed significantly and were in the following order： Zn（0.282 ） 〉Cd （0.234） 〉Cu （0.198 ） 〉Pb（0.014 ）. There were highly significant correlations between the contents of Pb, Cd, Cu and Zn in brown rice and in surface paddy soils, and the coefficients of correlation（r） were 0.905, 0.925, 0.939 and 0.957, respectively. The correlation between the Cd content and the ratio of Cd/Zn in brown rice was also highly significant（ r=0.837 ）. The ratio of Cd/Zn in brown rice was 0.002, which was far lower than the critical value of 0.015.