北京市不同区位耕作土壤中重金属总量与形态分布特征

采集北京市不同区位(中心城区、近郊平原、远郊平原)的代表性耕作土壤-麦粒匹配样品23组,分析不同人类活动强度影响下耕作土壤中重金属(Cd、Cu、Zn、Pb)全量、赋存形态以及生物有效性,并探讨其来源差异与健康风险.结果表明:①频繁的交通活动与工业释放致使中心城区(Pb平均含量为35.59 mg·kg-1)土壤呈现出较为明显的Pb富集特征,而长期污水灌溉等农业活动导致了近郊平原局部土壤重金属的明显积累.②土壤中Cu、Zn和Pb主要以残余态(35%～75%)与有机结合态(23%～53%)形式存在,其次是铁锰氧化态(1%～19%),而碳酸盐结合态(n.d.～5%)与离子交换态(n.d.～2%)含量非常少.Pb、Zn和Cu的生物可利用性从中心城区到近郊平原、远郊平原逐渐下降,Cd则呈相反的趋势.近远郊土壤中Cd的离子交换态(13%～31%)与碳酸盐结合态(11%～27%)占有相当高的比例,在4种重金属中生物可利用性最高.③Cd与Zn在麦粒中的含量与土壤中金属的铁锰氧化态含量正相关(P<0.05,r为0.43～0.57);④种植于中心城区与近郊土壤上的小麦籽粒中部分Zn、Pb含量超出了WHO限值,对当地居民健康构成潜在风险.

Total Contents of Heavy Metals and Their Chemical Fractionation in Agricultural Soils at Different Locations of Beijing City

In this study, 23 groups of suited typical soil-wheat grain samples were collected from different locations of Beijing city (central city, suburban plain and exurban plain), the accumulation, chemical forms and bioavailability of heavy metals in arable soils under different human activity intensity were analyzed, and their source identifications and health risk were discussed. The results showed that 1Urban soils exhibited Pb contamination with an average concentration (35.59 mg·kg^-1) above the WHO limit, probably due to the emission of traffic activities and industrial processes. In addition, long-term sewage irrigation and other agricultural activities led to local metal contamination in the suburban agricultural soils. 2Cu, Zn and Pb were predominantly associated with the residual (35%-75%) and organic (23%-53%) fractions, followed by Fe/Mn oxide (1%-19%), and very small proportion of carbonate (n. d. -5%) and exchangeable (n. d. -2%) fraction. Furthermore, compared with the suburban agricultural soils, Pb, Zn and Cu in the urban agricultural soils showed higher mobility, whereas the exurban agricultural soils presented the lowest mobility. For Cd, the order was contrary. Besides, Cd showed the highest bioavailability among the four metals in suburban and exurban arable soils due to its considerable proportion of exchangeable (13%-31%) and carbonate fractions (11%-27%). 3Cd and Zn contents in wheat grains were largely dependent on the Fe/Mn ox. fractions in the studied soils (P<0.05, r were 0.43-0.57). 4Pb and Zn concentrations in wheat grains in some of the urban and suburban agricultural soils were above the standard limit, which might bring potential risk for the health of the local residents.