污灌条件下重金属在耕作土壤中的积累与形态分布特征——以北京市通州区凤港减河污灌区农用地为例

Impacts of Sewage Irrigation on Heavy Metal Distribution and Chemical Fractions in Arable Soils: A Case Study About Sewage-irrigated Farmlands of the Fenggangjian River in Tongzhou District of Beijing, China

以北京市通州区凤港减河典型污灌农用地为研究对象,分析了污灌对耕作土壤中Cd、Cu、Zn和Pb的全量与形态分布特征的影响。结果表明：①土壤中Cu、Zn和Pb的含量均低于WHO（World Health Organization）限值,Cd的含量明显高于WHO限值。然而,4种重金属的污染负载指数（PLI为1.49~4.54）均高于1,其中Cd的PLI值最高,表明长期污灌已经导致耕作土壤中重金属的积累;②总体来看,随土壤深度的增加,重金属含量呈先减少,后增加的趋势。距离灌渠越远,土壤中重金属含量越少;③土壤中Cu、Zn和Pb主要以残余态和有机结合态形式存在,其次是铁锰氧化态,碳酸盐结合态和离子交换态非常少。而土壤中Cd的碳酸盐结合态与离子交换态占有相当大的比例。4种重金属的生物可利用性次序为：Cd〉Cu〉Pb〉Zn,且表土层高于底土层。同时,研究发现距离灌渠越近,表土层中Cd的生物可利用性越低。总的说来,污灌土壤中较高的Cd含量与其较高的生物可利用性对食品安全与人类健康构成了潜在风险。

In this study,distribution and chemical fractions of Cd,Cu,Zn and Pb in sewage-irrigated arable soils located in the sewage-irrigated farmlands of the Fenggangjian River in Tongzhou District of Beijing were investigated.The results showed that： 1） Cu,Zn and Pb concentrations in soils were below WHO limits,while Cd was obviously above the limit.However,due to long-term sewage irrigation,studied soil exhibited metals accumulation with their pollution load indices（1.49-4.54） above one,especially Cd with the highest PLI.2） On the whole,with soil depth rising,total contents of four metals presented firstly decreasing,then increasing trends.For metal fractions,Cu,Zn and Pb were predominantly associated with residual and organic fraction,followed by Fe/Mn oxide,and very small proportion of carbonate and exchangeable fraction,whereas,the carbonate and exchangeable fractions of Cd accounted for considerable proportion.Their mobility and bioavailability followed the sequence： CdCuPbZn.Besides,in topsoils,their bioavailability was higher than that of subsoils.3） Generally,the contents of heavy metals in soils showed a decreasing trend with the increment of the distance from the irrigation channel.Also,it was observed that the arable soils closer to the irrigation channel showed the lower Cd bioavailability in topsoils.Therefore,higher Cd contents and its higher bioavailability in sewage-irrigated soils might constitute potential risk on food security and human health.