杭州市居民区土壤重金属的化学特性及其与酸缓冲性的关系

CHEMICAL CHARACTERISTICS OF HEAVY METALS AND THEIR RELATIONSHIPS WITH ACID BUFFER CAPACITY OF SOILS IN RESIDENTIAL SITES IN HANGZHOU CITY, ZHEJIANG PROVINCE

杭州市居民区土壤中Cd、Cr、Cu、Ni、Pb、Zn、Mn和Mo均有不同程度的积累;除Cr、Mo外, 居民区重金属的积累一般低于该市商业区。居民区土壤中Cd、Co、Cr和Ni主要以稳定的残余态为主;而Cu、Pb、Zn和Mn则以可提取态为主。在正常条件下,居民区土壤具有较高的重金属吸持能力,被吸持的重金属较为稳定,绝大部分不易被中性盐所交换。但随着pH的下降,土壤对重金属的吸持能力明显降低,而重金属的释放潜力明显增加。杭州市居民区土壤的酸缓冲性有较大的变化,主要受土壤CaCO3含量的影响,缓冲性高的土壤,重金属可溶性较低。居民区土壤由于受建筑物质中CaCO3的影响,具较高的酸缓冲性,增加了土壤重金属的稳定性。

Sustainable management of urban soils to minimize their potential impact on the environment requires an understanding of factors influencing mobility of heavy metals in the soils. The objective of this study was to analyze concentrations, forms and acid solubilities of heavy metals in the soils from fifty residential sites in Hangzhou City. In addition, Pb, Cu, Zn, and Cd adsorption-desorption behavior, relationship between release of heavy metals and pH, and acid buffer capacity of the soils were also studied. The soils in the residential sites had been anthropogenically contaminated by heavy metals to a different extent. Except for Cr and Mo,however, concentrations of these heavy metals in the soils were found lower than those in the soils in commercial districts. Cd, Co, Cr and Ni were mainly in stable residual forms, while Cu, Pb, Zn and Mn were mostly in extractable forms. Generally the soils in the residential sites had a high capacity to adsorb heavy metals,so stably that they were not liable to get displaced by neutral salts. The capacity however, decreased with the decrease in pH, and release of heavy metals from the soils increased rapidly when soil pH went down below 4.0～6.0. The acid buffer capacity of the soils varied greatly and was mainly controlled by soil CaCO_(3) content. The heavy metals in soils with a high acid buffer capacity were low in solubility. Since the soils in the residential sites contained higher CaCO_(3) brought in by construction materials, they often had a high acid buffer capacity and thus enhanced stability of the heavy metals in the soils. Our data indicated that heavy metals of the soils from residential sites in Hangzhou City did not pose significant hazard to the environment in normal conditions.