Evaluation For Safety Utilization Of Agricultural Soils Contaminated With Heavy Metals Around The Mining Or Industrial Areas

An investigation was carried out over four agricultural areas near industrial and mining areas in order to realize the pollution with heavy metals in the soils and the safety for agricultural utilization.102 sampleas of syrface soils(0-20 cm)were collected and the available(DTPA-extractable)amounts of Cd,Pb,Ni,Cu,Zn were measured.Based on the available ocntents of the heavy metals,the soils were graded according to the safety for agricultural utilization.The main results were as follows:1.The four investigation areas are situated near different industrial or mining districts.Area A is near an industrial district dominated with hardware,machinery and leatherwear factories.Area B is distributed over a piedmont plain at the foot of a Pb-Zn mine.Area C is closed to a high and new technology development zone dominated by electronics and mhachinery factories.The leading industries in the base where area D is located are building materials,coal and machinery.2.The soils of the four areas belong to acidic soils.The mean available contents of Ni,Cu,Zn,Cd and Pb of the soils from area A were 0.37,2.0,5.38,0.08 and 2.64 mg·kg-1,respectively.The avarage available contents of Ni,Cu,Zn,Cd and Pb of the areaB soils were 0.54,2.61,2.75,0.205 and 5.48 mg·kg-1,respectively.The mean available Ni,Cu,Zn,Cd and Pb of the soils from area C were 4.32,18.20,1.92,0.063 and 2.58 mg·kg-1,respectively.As for area D,The avarage available contents of Ni,Cu,Zn,Cd and Pb were 0.24,3.69,4.15,0.14 and 4.85 mg·kg-1,respectively.3.The distribution of the heavy metals in the soils of each investigated area was different because of the different resources of pollution.Correlation analysis,factor analysis and principle component analysis showed that some heavy metals in the soils were homologous.The homologous groups included Cd,Zn and Pb(area A),Ni and Cu(area A),Cd,Zn and Ni(area B),Pb and Cu(area B),Cd,Zn,Ni and Cu(area C),Ni、Pb and Cd(area D),Cu and Zn(area D).4.The evaluation of pollution degrees of the heavy metals in the soils showed that some heavy metals exceeded the criterion of available soil heavy metals for agricultural production.In area A,4 points exceded the safety value of Cd while 1 point exceeded the limit value of Cd.The soils in area B was mainly polluted with Cd because 4 points exceeded the safety value of Cd while 4 points exceeded the limit value of Cd.The soils of area C was seriously polluted with Ni and Cu.The available Ni of 6 soils was higher than the limit value,of 12 points was higher than the dangerous value.There were also 12 soils containing higher Cu than the safety value,and 3 soils exceeded the limit value of Cu.As for area D,the available Cd of 9 soils was higher than the safety value where 2 points exceeded the limit value of Cd.5.The samping units of the fields in each investigation area were grouped into safe unit,alarm unit,limit unit and risk unit for agricultural cultivation,respectively.There were 1 limit unit of Ni,1 alrm unit of Ni,1 alrm unit of Cu,4 alarm units of Cd,and 1 limit unit of Cd in area A.In area B,there were 1 alarm unit of Ni,1 limit unit of Ni,4 alarm units of Cd,and 4 limit units of Cd.There were 3 alrm units of Ni,6 limit units of Ni,and 12 risk units of Ni in area C.There were also 12 alarm units and 3 limit units of Cu in area C.As for area D,there were 1 alarm unit of Zn,1 alarm unit of Cu,1 alarm unit of Ni,l alarm unit of Pb,9 alrm uints of Cd and 2 limit units of Cd.