Heavy Metals Pollution Characteristics And Evaluation In The Reclaimed Tidal Flat Soils And Crops In The Pearl River Delta

In this paper,the heavy-metal contamination of soil and crops in the coastal reclaimed farmland of the Pearl River Delta was evaluated respectively.The results showed that all the concentrations of Cu,Pb,Cd,Ni,Cr and Zn in soil samples were higher than the background values in Guangdong Province soils. Average contents of Cu,Pb,Cd,Ni,Cr and Zn in the soils are 56.06,48.30, 0.72,41.15,115.1 and 200.1 mg/kg respectively.Compared to the GradeⅡof soil environmental quality standards(GB15618-1995),the concentration of Cu in 73.7% soil samples,Cd in 88.6%samples,Ni in 59.6%samples and Zn in 28.9%samples exceeded the criteria.Based on the Nemerow index method and the China National Soil Environmental Quality Standards(GradeⅡ(pH＜6.5)),the average comprehensive pollutant index for heavy metals in soil was 1.86,which was classified as slight pollution.Evaluated by using Hakanson's Potential Ecological Risk evaluation Index,all ecological risk index RI in the region exceed 300 and can be severe ecological harm.Among them,Cd is the main pollution element.In the six heavy metals,the percentage of phyto-available chemical speciation is in order of Cd＞Pb＞Cu＞Ni＞Zn＞Cr.Compared with some standards such as "limits of pollutants in food",except Cu, all the other heavy metal content in crops exceeded the standard in some samples.The pollution degree of heavy metal in crops is Ni＞Pb＞Cr＞Zn＞Cd＞Cu.The degree of heavy metal contamination in different crops follows:roots＞fruit＞Solanaceae＞leaf. The heavy metals accumulation factor in crops is in order:Cd＞Zn＞Ni＞Cu＞Pb＞Cr.It is obvious that the reclaimed tidal flat soils and crops in the Pearl River Delta were polluted with heavy metals significantly,especially Cd in soil and Ni,Pb and Cr in crop.