Study Of Characteristic On Heavy Metal Contamination And Risk Assessment Of Soil And Plant Along Roadsides Of The Northwestern Sichuan Plateau,China

Traffic activities in roadways are the major resource of the heavy metal contamination on the Northeastern Sichuan Plateau,China.In order to characterize the spatial pattern of heavy metal distribution we collected soil and Saussurea nigrescens samples and measured the concentrations of five heavy metal species(Cd,Cu,Ni,Pb,Zn)from nine sites in Hongyuan County of Sichuan province,including three transects reflecting typical gradients of traffic density,each transect consisting of three levels of traffic density sites,and in order to assess the ecological risk of the heavy metal contamination we calculated single pollution index,Nemerow multi-factor index method and potential ecological risk index.Based on these result,conclusions are as follows:(1)The mean heavy metal concentration of soil decreased following the order Pb > Cr >As >Ni > Zn > Cd > Cu,which was consistent with the order of meadow soil background value.The soil of study sites was up to the quality standard of soil environment of the nature reserve.According to meadow soil background value,the study sites were heavily contaminated by Cd and slightly polluted by Ni,Pb and Zn.(2)Results showed that the soils were contaminated by Cd and Zn,whose concentrations were higher than the natural soil background values in all sampling sites.Moreover,Cd and Zn concentrations increased with increasing traffic density,suggesting that traffic activities were potentially responsible for the metal contaminations.Cd and Cu concentrations of Saussurea nigrescens increased with increasing traffic density.Other heavy metals of Saussurea nigrescens had no tendency with traffic density.(3)The clustering of heavy metals in soil showed that metals could be divided into three major groups: Cd and Zn was the first one,Ni and Cu was the second,and Pb was the third;In plants,metals also could be divided into three major groups: Cd and Cu was the first cluster,Ni and Pb was the second,and Zn was the third.The clustering of heavy metals in soil was more closely related to the law of the periodic table arrangement.(4)According to bioconcentration factors,the intake capabilities of heavy metals from soil to Saussurea nigrescens was in the order of Cd>Zn>Cu>Pb>Ni,which was not consistent with the order of the concentration of heavy metals in soil.(5)Correlations between heavy metals in soil showed that more significant positive correlations between metals in the sites with high traffic density were observed than that in the sites with low traffic density.Fewer correlations of heavy metals of plant were observed in all sites.The influence of transport activities on the accumulation of heavy metals in plants is less obvious than that of in soil.(6)According the standard of safety and sanitation at food,Pb reached hazardous level,Pb from sites with high traffic density reached hazardous level,Cu,Zn reached safety level.(7)According to single pollution index indicate that the study sites were heavily contaminated by Cd and slightly polluted by Ni,Pb and Zn,and according to Nemerow multi-factor index and potential ecological risk index,the study sites areas were suffering moderate potential ecological risks.More specifically,the sites with high traffic density were moderately contaminated and the sites with low traffic density were mildly contaminated.In general,Cd and Zn have highly accumulated in soils of the study region and hence attentions should be paid on the high ecological hazard associated with soil heavy metal contaminations even in the undeveloped regions.