中水灌溉下重金属在土壤中的垂直迁移及其对地下水的污染风险

中水灌溉是解决水资源短缺的潜在途径,关于中水灌溉条件下土壤中重金属的迁移行为及其对浅层地下水的污染风险至今仍缺乏研究。本文通过土柱模拟试验,分析中水灌溉条件下重金属在土壤中的迁移趋势及其对浅层地下水的污染风险。试验用添加重金属（As、Cd、Cu、Pb浓度分别为2、0.2、20、20 mg.kg-1）的人工污水和中水以1年、3年的灌溉量进行土柱淋溶实验。结果表明,淋溶20天（1年的灌溉量）以及60天（3年的灌溉量）,灌溉水中的As、Cd、Cu和Pb主要在表层（0¹0cm）累积。随着淋溶时间的延长,4种重金属（尤其是Cd）表现出向下迁移的趋势。但与地下水I级水质标准（GB/T14848-93）相比,淋滤液中4种重金属均未超标。因此,从本文的模拟试验来看,以北京市当前的中水进行灌溉,As、Cu、Pb对浅层地下水的污染风险不大。

Leaching of heavy metals in soil column under irrigation reclaimed water:a simulation experiment

Irrigation using reclaimed water would be the potentially effective approach to meet the large demand of agriculture. However,the environment risks of reclaimed-water irrigation still remain unknown.To obtain the knowledge of the impact on soil,crops and shallow groundwater,an investigation was undertaken in Tongzhou,Beijing.As one part of the research,soil column experiments(10 100 cm) were conducted to understand the heavy metal transport behaviors in soil profile under reclaimed water leaching condition and the concentrations of As,Cd,Cu,and Pb in the leachate.Soil columns were leached with artificial reclaimed water(As,2 mg kg~(-1);Cd,0.2 mg kg~(-1);Cu,20 mg kg~(-1);Pb,20 mg kg~(-1)) and reclaimed water(As,0.83g kg~(-1);Cd,0.01g kg~(-1);Cu,1.73g kg~(-1);Pb,2.01g kg~(-1)) in different water amount(4 L,12 L).The results indicated that the maximum values of total As,Cd,Cu and Pb in the superficial horizons(0-20 cm) in soil columns are either artificial reclaimed water leaching or reclaimed water leaching.The trends of heavy metals downward movement were showed with the increase of leaching water amount and Cd demonstrated more mobile in soil columns than other heavy metals,while the mobility of As,Cu and Pb were weak.According to the leachate concentrations of As,Cd,Cu and Pb,which did not exceed the values of the Groundwater Quality Standards I,it could be concluded that irrigation with reclaimed water would not result in heavy metals(As,Cd,Cu and Pb) pollution on the shallow groundwater under reclaimed water leaching condition in this study,and As,Cu and Pb indicate a lower pollution risk to the shallow groundwater than Cd under long-term reclaimed water irrigation condition.