土壤—农作物系统中重金属元素迁移转化规律研究——以湖北宣恩县为例

Study on the Migration and Transformation Law of Heavy Metals in Soil-crop System

为研究土壤中重金属元素在不同作物系统中的迁移转换规律及其控制影响,采集湖北宣恩地区的茶叶、水稻、玉米、土豆、黄金梨、白柚及其对应的根系土样品,对根系土中的重金属元素含量、生物可利用性、内梅罗综合污染指数以及农作物中的重金属富集程度进行分析。结果表明,农作物土壤中Cd平均含量显著高于宣恩县土壤背景值。评价区土壤中Pb、Hg、As、Cu和Zn等重金属元素主要为强有机结合态(F6)与残渣态(F7),很难以离子形态释放出来,而Cd在土壤中的赋存形态主要为水溶态(F1)和离子交换态(F2),占比高达35. 59%,很容易被生物吸收利用。评价区水稻根系土已经遭受Cd污染,农作物重金属污染一方面与土壤背景值有关,另一方面与生物可利用性相关。除玉米茎部特别富集Cd和水稻根部特别富集As外,所收集的农作物可食部分从根系土中转移Pb、Cd、Hg、As、Cu和Zn等6种重金属元素的能力很弱。

In order to study the law of soil heavy metal migration and transformation in different crop systems and its control effects,collecting tea,rice,maize,potatoes,gold pear,white shaddock and their corresponding root soil samples in Xuanen county of Hubei Province,the contents of heavy metal elements,bioavailability,the comprehensive contamination index and the degree of heavy metal concentration in crops are analyzed.The results show that the average content of Cd in crop soil is significantly higher than that in Xuanen county.Heavy metal elements such as Pb,Hg,As,Cu and Zn in the soil of the evaluation area are mainly fraction bound to organic matter(F6)and residue fraction(F7)which is difficult to release the ion form,while the occurrence form of Cd in the soil is mainly water soluble states(F1)and ion exchange states(F2),accounting for up to 35.59%,which is easy to be absorbed and used by organisms.The rice root soil in the evaluation area has been contaminated with Cd,heavy metal pollution of crops is related to soil background value on one hand and bioavailability on the other.In addition to the special enrichment of Cd in maize stems and As in rice roots,six heavy metal elements,such as Pb,Cd,Hg,As,Cu and Zn,are weakly transferred from the edible part of the collected crop from the root soil.