复合污染农田土壤镉、铅迁移对水环境的影响

Effects of lead and cadmium migration on water environment in compound polluted farmland soil

  • 摘要:目的】探究复合污染农田土壤重金属镉(Cd)和铅(Pb)在土壤和水环境中的迁移行为,综合分析农田土壤Cd和Pb迁移对地下水环境的污染风险,为降低农田土壤污染区域地下水环境污染风险提供参考依据。【方法】以含Cd和Pb的复合污染农田土壤地表径流为研究对象,在自然降水条件下进行坡地径流试验;以受重金属污染的玉米和马铃薯种植区为监测区域,在自然降水条件下进行田间监测试验,并对地表径流中Cd和Pb含量与不同监测参数进行相关分析;以含Cd和Pb的复合污染农田土壤地下渗流为研究对象,采集3个不同污染水平(自然轻度污染、自然重度污染、人工重度污染)的土壤进行室内土柱淋溶试验。测定土壤理化性质和水样指标,评估Cd和Pb对地下水环境的污染风险。【结果】坡地径流试验结果显示,地表径流中Cd和Pb含量随降水场次的增加呈下降趋势,且迁移距离越远,Cd和Pb含量越低,其中迁移距离为1.25 m时,地表径流中Cd和Pb含量均在第1场降水时达最高值,分别为0.1729和2.2809 mg/L;地表径流中Cd和Pb含量严重超标,且Cd随径流迁移对地下水环境的污染风险高于Pb。田间监测试验结果显示,玉米和马铃薯种植区的Cd含量分别于第2场和第4场降水结束时达最高值和最低值;Pb含量分别于第3场和第5场降水结束时达最高值和最低值;玉米种植区的地表径流中Cd和Pb迁移存在地表水环境重金属污染风险,马铃薯种植区的地表径流中Cd和Pb迁移不存在地表水环境重金属污染风险;相关分析结果显示,地表径流Cd和Pb含量与大气沉降Cd通量、大气沉降Pb通量和降水量呈极显著(P<0.01,下同)或显著(P<0.05,下同)正相关,与土壤pH呈极显著或显著负相关。室内土柱淋溶试验结果显示,在不同污染水平下,土壤淋溶水中Cd和Pb含量随淋溶时间的增加整体呈降低趋势,其中自然重度污染和人工重度污染水平的浅层土壤淋溶水中Cd含量超标,存在地下水环境污染风险;自然轻度污染土壤中的Cd和Pb含量相对较低,对地下水环境无污染风险。玉米种植区浅层土壤Pb随地下渗流迁移的地下水环境污染风险高于Cd,而马铃薯种植区浅层和深层土壤Cd的地下水环境污染风险高于Pb。【结论】复合污染农田土壤中的Cd和Pb随地表径流和地下渗流迁移行为存在一定地下水环境污染风险,且Cd对地下水环境的污染风险较Pb高。地表径流Cd含量和地表径流Pb含量与大气沉降Cd通量、大气沉降Pb通量、降水量和土壤pH相关。

     

    Abstract:Objective】This study aimed to investigate the migration behavior of heavy metals cadmium (Cd) and lead (Pb) in farmland soil with compound pollution within soil and water environments, comprehensively analyze the pollution risk of Cd and Pb migration to groundwater environment, providing a reference for mitigating groundwater pollution risks in polluted farmland areas.【Method】Taking the surface runoff of farmland soil with compound pollution of Cd and Pb as the research objects, slope runoff experiments were conducted under natural precipitation conditions. Taking maize and potato plantation areas polluted by heavy metals as monitored areas, field monitoring tests were carried out under natural precipitation conditions, and correlation analysis was performed between Cd and Pb contents in surface runoff and different monitoring parameters. Taking the subsurface flow of farmland soil with compound pollution of Cd and Pb as the research objects, soils in three different pollution levels (mild natural pollution, severe natural pollution, and severe anthropogenic pollution) were collected for indoor soil column leaching tests. Soil physiochemical properties and water sample indexes were determined to evaluate the pollution risk of Cd and Pb on underground water environment.【Result】The results of slope runoff experiments indicated that the Cd and Pb contents in surface runoff exhibited a decreasing trend with the increase in rainfall events. Furthermore, the longer the migration distances, the lower the Cd and Pb contents. At the migration distance of 1.25 m, the highest values of Cd (0.1729 mg/L) and Pb (2.2809 mg/L) contents were both observed during the first precipitation event, significantly exceeding environmental standards, and the pollution risk of Cd migration via runoff to the groundwater environment was higher than that of Pb. The field monitoring test results showed that in maize and potato plantation areas, Cd contents reached their maximum and minimum values at the end of the second and fourth precipitation events, respectively; Pb contents reached their maximum and minimum values at the end of the third and fifth precipitation events, respectively. The migration of Cd and Pb in surface runoff in the maize plantation areas posed a heavy metal pollution risk to the surface water environment, whereas no such risk was observed in the potato plantation areas. Correlation analysis revealed that Cd and Pb contents in surface runoff had extremely significant (P<0.01, the same below) or significant (P<0.05, the same below) positive correlations with atmospheric deposition flux of Cd, atmospheric deposition flux of Pb, and precipitation amount, while had extremely significant or significant negative correlations with soil pH. The indoor soil column leaching test results showed that under different pollution levels, the Cd and Pb contents in soil leaching water generally exhibited a decreasing trend as leaching time increased. The Cd content in leaching water of shallow soil with severe natural pollution and severe anthropogenic pollution exceeded the standards, posing a pollution risk to the groundwater environment. The Cd content in soil with mild natural pollution was relatively low, posing no pollution risk to the groundwater environment. In maize plantation areas, the pollution risk of groundwater environment of Pb migration from surface soil to subsurface flow was higher than that of Cd. In contrast, in potato planting areas, the pollution risk of groundwater environment of Cd in both shallow and deep soil was greater than that from Pb.【Conclusion】The migration behavior of Cd and Pb in farmland soil with compound pollution via surface runoff and subsurface flow poses pollution risks to the groundwater environment, with Cd exhibiting higher pollution risks than Pb. The Cd and Pb contents in surface runoff are correlated with the atmospheric deposition flux of Cd, atmospheric deposition flux of Pb, precipitation amount and soil pH.

     

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