Samples of surface and gutter sediment from roads within N.W. London have been analyzed for levels ofCd, Cu, Fe, Mn, Pb, and Zn. Sediment and associated metal grading curves are presented and apart from Mn and Fe which reflect natural background levels, the remaining metals show distributions which relate to road type and traffic conditions. For highways carrying the highest traffic densities the concentrations of Cd and Ph are greatest for grain sizes between 100 and 500 lam and an aggregation process is postulated. Residential side street samples show a marked affinity of Cd, Fe, and Zn for the coarsest grain fractions.
Laboratory sorption and desorption studies are described and solution concentrations are obtained for Cd, Cu, Mn, Pb, and Zn over 1 to 30 day time periods. Solubility curves are typically variable with time. The relationship of leachate patterns to particle size and sample site location is discussed and its relative importance to stormwater loadings is considered. Extraction efficiencies for the five metals are found to be independent of road type and in the order Cd > Zn, Cu > Mn > Pb. The relevance of this hierarchy to stormwater toxicity is discussed.