Metal extraction from road sediment using different strength reagents: Impact on anthropogenic contaminant signals

Washoff of road deposited sediment into storm drain systems is one of the m ajor contributors to nonpoint source pollution in urban fluvial networks. T hese sediments contain a variety of potentially toxic organic and inorganic contaminants. Road sediment from 13 locations in an urban (non-industriali zed) drainage basin, and soil from 10 background (control) locations were c ollected to assess total and labile fractions of Al, Co, Cu, Fe, Mn, Ni, Pb and Zn. Four digestions, of varying strength, were used to assess contamin ant levels, these included: a total four-acid digestion, a microwave-assist ed digestion with concentrated nitric acid (USEPA Method 3051), a 0.5 M `co ld' HCl, and a 0.05 M EDTA (pH 7). Road sediment data indicate that Al, Co, Fe, Mn and Ni were primarily lithogenic in origin, while Cu, Pb and Zn sho wed very significant anthropogenic signals, most probably from vehicle-rela ted sources. Median Pb concentration enrichment ratios for the EDTA extract ion were about 42, indicating an extreme anthropogenic signal. The weak ext ractants (HCl and EDTA) are considered in this study to be superior in thei r ability to characterize the degree of anthropogenic contamination and sho uld be utilized more widely in environmental contaminant studies.