Assessment of heavy metals contamination and leaching characteristics in highway side soils, Iran.

Twenty seven topsoil samples were collected under stable weather conditions from the northern and southern sides of Tehran-Karaj Highway, Iran. Samples were analyzed for heavy metal (Pb, V, Zn, Ni, Co, Cr, Cd, and Mn) contents and leaching characteristics. The results showed that all heavy metal contents except Cr, Mn and Co are higher than acceptable values in natural soils. High contents of these elements could be attributed to anthropogenic effects related to traffic sources. Toxicity characteristics leaching procedure (TCLP) test results reveal that the studied soils may be hazardous. Statistical analysis shows significant positive correlations between heavy metals and organic matter. Also a significant correlation was observed between Cd, Pb and Zn. This affinity and exponentially decreasing concentration with distance from the edge of the road suggest that automobiles are a major source of these metals in the roadside soils. Use of leaded gasoline and tire erosion gives a boost to this claim.