甘肃白银东大沟地区土壤镉地球化学特征及生态风险评价

Geochemical Characteristics of Cadmium,and Ecological Risk Assessment of Soil in Dongdagou Area,Baiyin City,Gansu Province

甘肃白银是中国重要的有色金属基地,历史上不科学不合理的矿产资源开发和农业生产活动,造成白银市及其周边部分地区重金属严重超标。重金属生物有效性控制因素和生态风险预测,一直是元素生物地球化学行为研究非常关注的问题。本文调查研究了白银东大沟灌区及其周边根系土与玉米籽实污染情况,分析东大沟灌区农业集中区土壤2007年与2018年关键指标变化情况,并综合评价玉米种植区生态风险。研究区土壤中局部地段Cd含量超标,平均值17.48 mg/kg,最高值达到51.1 mg/kg,不同形态Cd含量相对大小依次为碳酸盐态>离子交换态>铁锰氧化态>腐殖酸态>强有机态>残渣态≫水溶态,高pH值碱性土壤和低镉积累的耐镉型玉米品种等因素限制了土壤中Cd的生物有效性,玉米籽实超标率仅为8.8%。东大沟灌区玉米地集中种植区内存在一定的Cd污染,但已得到有效控制,制约Cd生物有效性的pH值、Corg和CaO含量一半以上点位呈现升高趋势,可确保现在和未来一段时间内仍将继续保持低风险。为更好地做好东大沟灌区内Cd含量超标区管控,建议继续选择低镉积累的耐镉型玉米品种种植,同时成熟期收获籽粒作为动物饲料或发展玉米种子资源产业,其他部位尤其是根部可作为修复部分进行回收处理,实现“边生产、边修复”的目的。

Baiyin is an important non-ferrous metal province in China.Historically,unscientific and unreasonable mineral resource development and agricultural production activities have breached the heavy metal standards in Baiyin city and its surrounding areas.The controlling factors of bioavailability and ecological risk prediction of heavy metals have always been of great interest in biogeochemical behavior research.In this study,we investigated the contamination of root soil and corn seeds in/around the Dongdagou irrigation area(Baiyin city),analyzed the changes of key soil indicators in 2007 and 2018 in the local agricultural concentration area,and evaluated the ecological risks in the corn growing area.The local soil Cd content(average 17.48 mg/kg,maximum 51.1 mg/kg)exceeds the standard in some areas.The relative Cd content in different forms is carbonate state>ion exchange state>iron and manganese oxidation state>humic acid state>strong organic state>residue state≫water-soluble state.Factors such as high pH alkaline soil and low Cd accumulation of Cd-tolerant corn varieties limited the Cd bioavailability in the soil,and the exceedance rate of corn seeds is only 8.8%.There is certain Cd pollution in the local corn concentrated planting area,but it has been effectively controlled.Over half of the points of pH,Corg and CaO content that constrain the Cd bioavailability show an increasing trend,which imply that the risk will remain low for the coming future.To better control the areas with higher Cd content than the standard,we recommended to continue to choose low Cd accumulation of Cd-tolerant corn varieties for planting,and to harvest the seeds at maturity as animal feed or develop the corn seed resource industry.We also proposed to conduct recycling of other parts,especially the roots as restoration parts,to achieve reduction while restoration.