Heavy Metals Pollution in the Soil of Guangzhou Wanmu Orchard:Investigation and Assessment

Based on investigation and sample analysis,environmental quality of orchard soil was assessed using Geoaccumulation index,Single-Factor Pollution Index and Nemerow Synthetical Pollution Index,in order to find out the spatial and vertical distribution characteristics of heavy metals in the Wanmu Orchard soil,and to address causes of the contamination and provide pollution control advices.The results indicated that Cd pollution is the most serious in the orchard soil,followed by Cu and Zn pollution,and Pb pollution is slight;In a plan called Guangzhou Wanmu Orchard Reserve Planning which divides orchard lands into three conservation districts of three grades,the quality of soil in the first-grade conservation district is clean(its Nemerow Synthetical Pollution Index is 0.732),soil in the second-grade conservation district is slightly polluted(in which Cd is the dominant pollutant,followed by Cu),and soil in the third-grade conservation district is heavily polluted by Cd(its Single-Factor Pollution Index is 6.390 and its Nemerow Synthetical Pollution Index is 4.699,both at heavy pollution level).The content of Cd increases with depth,while that of Pb,Cu and Zn decrease.Compound pollution of Cu and Zn is ubiquitous in the orchard soil.These show that agriculture pollution source is the uppermost one for the first-grade conservation district,agricultural pollution source and industry pollution source exist in the second-grade conservation district,and industry pollution source is the root cause for pollution in the third-grade conservation district.Chemical pollution remediation and ecological agriculture can be applied to control heavy metal pollutions in the soil.