如何准确、客观表征再生水长期灌溉的重金属污染风险是人们关注的主要问题之一。研究通过调查不同水源灌溉条件下土壤、小麦重金属含量,结合不同输入途径对再生水灌区土壤重金属的贡献,评估再生水灌溉对土壤、农作物的重金属污染风险。结果表明,污灌区、再生水灌区土壤均呈现不同程度的重金属累积,但不同灌区小麦籽粒的重金属含量之间没有差异。北京市再生水重金属浓度远远低于农田灌溉水质标准,再生水灌渠中采集的水样重金属浓度与地下水重金属浓度之间的差异并不显著。通过再生水灌溉途径带入的重金属与地下水灌溉相当,低于大气沉降和有机肥施用等输入途径带入的重金属。当前再生水灌溉导致土壤重金属污染的风险较小,并不会导致农作物重金属超标。再生水灌区土壤重金属污染并不一定是由于再生水灌溉导致,更大程度是早期的污水灌溉或有机肥施用造成的。
It was difficult to precisely assess the risk of heavy metals pollution of reclaimed water irrigation by field survey due to the shortage of irrigated area of long-term irrigation with reclaimed water and the interference cased by wastewater (sewage sludges) used in some reclaimed water irrigated area. The objective of this paper was to assess the pollution risk of heavy metals with reclaimed water irrigation by investigating the areas irrigated with irrigation water from different channels and comparing the heavy metals input from three different channels in the irrigated area. Compared to heavy metal concentrations of soils irrigated by groundwater, heavy metals were accumulated in the soils of wastewater irrigated area and reclaimed water irrigated area to a larger extent. However, there observed no significant difference in heavy metals concentrations of wheat grain sampled from different irrigated areas. Further investigation on the effluent of Beijing wastewater treatment plants and water sampled from Beiyechang irrigation canal showed that the heavy metal concentrations of reclaimed water were much lower than the standards for irrigation water quality. The input of heavy metals by reclaimed water irrigation was close to the input of heavy metals by groundwater irrigation, and was lower than the input by atmospheric deposition and organic fertilizer application. It was proposed that the risk of heavy metals caused by reclaimed water irrigation was small. Compared to early findings about environmental pollution of Beijing in 1976, the present study showed that the current heavy metal pollution of soils in the reclaimed water irrigated area did not necessarily result from reclaimed water irrigation but to a larger extent was caused by early wastewater irrigation (sewage sludges) or organic fertilizer application and atmospheric deposition.
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