Safe Utilization Evaluation Of Agricultural Land Polluted By Heavy Metals

Heavy metal pollution in agricultural land will affect crop yield and quality,and then threaten human health.The traditional evaluation of heavy metal in agricultural land is only a single study of soil or crop edible parts,cannot fully reflect the excessive degree of heavy metal in agricultural land.This paper explores a new method for safety utilization evaluation of agricultural land combined with soils and crops,and take X town as the study area to conduct empirical research,aiming at a more comprehensive understanding of the excessive situation of heavy metal in agricultural land.And the results show that:(1)In this paper,the evaluation of limits of soil heavy metal that exceed standards are integrated with existing soil environmental quality assessment and food safety evaluation in different pH values of soil and different land use types.Relying on the "soil environmental quality standard"(GB15618-1995)to determine the standard values of heavy metal in the soil of paddy field,dry land,irrigated land,orchard,grassland and woodland.The standard value of heavy metal content in orchard soil was determined by the “evaluation standard of environmental quality of producing area of edible agricultural products”(HJ/T332-2006).The standard value of soil heavy metals in tea garden was determined with the “technical condition of tea habitat environment”(NY/T853-2004).The heavy metal in the soil and the edible parts of rice and wheat were evaluated respectively.Combining with soil and crops,the safe use evaluation of heavy metals in agricultural land was carried out.The results of the evaluation were characterized by excessive rate,safety utilization grade and evaluation grade map.(2)The surface soil of agricultural land in the study area is mainly polluted by Cd,the excessive rate was 32.08%.Ni and Hg were slightly exceeded,and the excessive rates were 13.21% and 5.66%.As,Pb,Cr,Cu and Zn were not exceeded.Rice samples were most polluted by Cd.And rice samples in the study area are also polluted by Pb and Cr,which are also mild excessive.Hg,As,Cr which in Wheat samples were not exceeded,Cd has the greatest impact to wheat,followed by Pb.(3)Evaluate the safe utilization of agricultural land by combining soil and rice,the proportion of agricultural land areas with no risk,slight risk,low risk,moderate risk and high risk is respectively 48.97%,17.34%,15.69%,8.97%,9.03%.Evaluate the safe use of agricultural land by combining soil and wheat,the proportion of agricultural land areas with no risk,slight risk,low risk,moderate risk and high risk is respectively 49.58%,14.28%,8.10%,9.01%,19.02%.Evaluate the safe use of agricultural land by combining soil and rice and wheat,most of the area are at no risk.The proportion of agricultural land areas with no risk,slight risk,low risk,moderate risk and high risk is respectively 44.18%,19.39%,8.44%,8.99%,19.01%.Most of the northwest and southeast regions of the study area and the southeastern part of the study area are free from risk.Most of the northeast and the west-central are at a slight risk.A small part of the central region is at low risk.Some parts of the south are at a moderate risk.The east-central section and parts of southeast of the study area are at a high risk.Corresponding safe utilization strategies are put forward according to different risk grades of agricultural land.And some suggestions on prevention and control of soil pollution are put forward.Comparing to respectively evaluating heavy metal in soil or crops,this method is more rigorous and comprehensive.