Assessing Feasibility Of Land Use Change In Heavy Metal Polluted Farmland

Currently,the problem of soil heavy metals endangering human health and the ecological environment has received widespread attention from various countries.More and more heavy metals are discharged into the soil,and sewage irrigation has also become one of the main reasons for soil heavy metal pollution.The problem of soil heavy metal pollution caused by mineral mining and smelting in Baiyin City,Gansu Province is particularly prominent.This study is based on the pollution investigation and risk assessment of heavy metal farmland in Dongdagou,Baiyin City,as well as the feasibility study and remediation effect assessment of land use type change,in order to provide scientific basis for pollution control and risk management of contaminated farmland in Baiyin City.The main contents and achievements of this study are as follows:（1）Taking Dongdagou heavy metal polluted farmland in Baiyin City as an example,a single factor pollution index was used to study the surface and various layers of soil in the polluted farmland.The results showed that:In the surface soil of the study area,areas A and D have the highest accumulation of As,while areas B～C,E,and F have the highest accumulation of Pb.There is slight pollution of As in area F.From the profile analysis,the overall downward migration of heavy metals is severe.The Nemero comprehensive pollution index indicates that there is severe pollution in the surface soil,and the E zone is the most severely polluted in the 0.5-0.75m deep soil;The deep soil layers of 0.75～1.5m are mainly non polluting areas.Pollution source analysis shows that heavy metals in Dongdagou soil mainly come from industrial and mining pollution,agricultural chemical inputs,and sewage irrigation.（2）Taking arsenic,cadmium,copper,and zinc as key pollutants of concern,human health risk assessment was conducted on different contact modes of five pollutants,and the results showed that:Taking arsenic,cadmium,copper,and zinc as key pollutants of concern,human health risk assessment was conducted on different contact modes of five pollutants,and the results showed that:The main carcinogenic risk contributions of cadmium and arsenic are inhalation of indoor particulate matter and oral intake pathways,respectively.Among them,the comprehensive carcinogenic risk of arsenic to future sensitive populations and construction workers can reach 5.41×10^-4 and 4.85×10^-5,respectively,have acceptable and unacceptable carcinogenic risks.Cd and As pose a non carcinogenic risk to future sensitive populations,while Cd,As,and Cu in some areas pose a non carcinogenic risk to construction workers.The adult blood lead model（ALM model）was used for risk assessment of adults（women of childbearing age）at this site,and the results showed that:Areas A～C,E,and G cause fetal blood lead levels exceeding10μg/L,the maximum probability of occurrence of g/L events exceeds 50%,indicating a higher risk of fetal blood lead content.Therefore,it is necessary to control and repair the heavy metal pollution in the soil of the research area.（3）The risk control values for arsenic,cadmium,copper,zinc,and lead calculated through the risk model are 1.35mg/kg,18.89mg/kg,6611.57mg/kg,49586.78mg/kg,and 610mg/kg,respectively.Considering the background value of the contaminated land and the reachability and economic principle of the treatment project,the remediation target values of As,Cd,Cu,Zn and Pb are set to 60mg/kg,20mg/kg,6611.57mg/kg,500mg/kg and 480 mg/kg respectively.（4）The leaching content of heavy metal pollutants（As,Cd,Cu,Pb,and Zn）in the stabilized and repaired soil was measured using the SPSP method.Compared with the target values for construction land remediation,the results showed that:Except for the only point in the bottom and sidewall of Zone B,which is the As content,and the only point in the bottom and sidewall of Zone B,which is slightly higher than the repair target value of Zn,all other points are far below the standard value.Compared with the soil risk screening value for agricultural land,the heavy metal content at all points on the sidewall of each area exceeds the soil risk screening value for agricultural land.Therefore,it is recommended to change the restored farmland to construction land.（5）Feasibility analysis shows that converting farmland into construction land is technically,economically,socially,and politically feasible,and can increase the income of local residents,improve the living environment of surrounding residents,eliminate potential human hazards,reduce water pollution hazards,and comply with future land use planning.It has played a promoting role in the material and cultural life of local people,and has high social value.