Heavy metal concentrations and pollution assessment of riparian soils in Shandong Province
山东省部分水岸带土壤重金属含量及污染评价

A total of 39 riparian soil samples were collected in 24 rivers,five reservoirs and Dongping Lake in Shandong province from September to October 2010.Concentrations of heavy metals,such as Cr,Co,Ni,Cu,Zn,Cd,Pb and Hg,as well as some basic physiochemical properties,including pH,particle size and organic matter content,were measured.Using the soil background concentrations of heavy metals in Shandong Province as standards,single factor indices and comprehensive indices of heavy metals were calculated to assess the degree of heavy metal contamination.The potential ecological risk index method was applied to evaluate the ecological risk of heavy metal contamination in riparian soil.The results showed that the riparian soil was mainly alkaline with a pH range of 5.67—8.66.The organic matter content was 2.60—33.74 g/kg with an average of 9.39 g/kg.The riparian soil had coarse granularity with an average particle size of 89.69 μm.Silt and sand grains were the main particles in riparian soil with average volume fractions of 50.33% and 38.48%.The average concentrations of Cr,Co,Ni,Cu,Zn,Cd,Pb and Hg were 53.03 mg/kg,10.33 mg/kg,24.96 mg/kg,18.38 mg/kg,56.13 mg/kg,0.142 mg/kg,22.48 mg/kg and 0.020 mg/kg,respectively.Heavy metal concentrations in the riparian soil samples were all lower than the heavy metal limit values of the class II environmental quality standard for soils in China(GB15618—1995).Heavy metal pollution in riparian soil was generally low and posed low ecological risk.The degree of contamination of the different heavy metals decreased as follows: Cd>Hg>Ni>Zn>Pb>Cr>Cu>Co and the potential ecological risk were in the order of Cd>Hg>Ni>Pb>Cu>Co>Cr>Zn.Thus,Cd and Hg most contributed to the ecological risk with average ratios of 46.8% and 33.6%.A higher degree of heavy metal pollution was found in riparian soil from Zhu Zhaoxin River,Liaohe River,Menlou Reservoir and Dongping Lake than riparian soil from other water source areas.Correlation analysis revealed that heavy metal concentrations were significantly and positively correlated with each other,and also with organic matter;in contrast,they were negatively correlated with average particle size.Hierarchical cluster analysis,based on Pearson correlation coefficients,was used to identify the sources of heavy metals in the riparian soils.The results suggested that the heavy metal concentrations in riparian soils were determined by both the soil parent materials and external sources related to human activities.Specifically,Cr,Co,Ni and Cu largely originated from soil parent materials;Zn and Cd were associated with contaminated surface runoff,Hg might be related to industry and domestic solid waste,and Pb probably derived from vehicle emissions.