Abstract:

Heavy metal concentrations and basic properties including pH values,particle size and content of organic matter were analyzed in a total of 90 street dust samples collected in July,2003 and April,2004 from three small towns in Shanghai suburban area.The results showed that the three different small towns presented similar temporal and spatial distribution characteristic for pH,particle size and organic matter as well as heavy metals.The pH values of the street dust were 841~1137,which assume alkaline.The average content of organic matter in street dust was 3413 g/kg.The street dust had coarser particle size than soil around,and the average particle size was 1736 μm.Sand grain was the main particles in street dust with the average volume fraction 70%.The particle size of street dust mainly showed unimodal or bimodal distribution spectrum,where the first mode was 250~300 μm,and the second was 30~50 μm.The average heavy metal concentrations were much higher than the soil background values of Shanghai city,but lower than those of Shanghai urban area.Cr and Ni concentrations showed significant seasonal change,which were higher in July (summer) and lower in April (spring).Higher concentrations of Cd,Cu,Pb and Zn were distributed mainly in the towns residential area,commercial area and scenic area as well as the township roads than in rural area.The prominent correlation between Cr and Ni,Cu and Pb,Cu and Zn,Pb and Zn,Fe and Mn might suggest the two possible sources of heavy metals in street dust;one might be related to vehicle transportation,and the other might be natural source such as soil.Moreover,significant correlation between organic matter and heavy metals indicated that organic matter was the carrier of heavy metals in street dust