Characterization of selected element concentrations and enrichment ratios in background and anthropogenically impacted roadside areas

Previous research by the National Contaminant Biomonitoring Program found fish from Manoa Stream, Hawaii, to have the highest concentrations of Pb in the nation. To explore possible source linkages we sampled background (uncontaminated) soil, roadside soil, and road deposited sediment in Manoa watershed and analyzed them for total and extractable concentrations of Al, Co, Cu, Fe, Mn, Ni, Pb, and Zn. Our concentration and enrichment ratio data indicate that Al, Co, Fe, Mn, and Ni were controlled by natural source variations, and Cu, Zn, and particularly Pb were anthropogenically enhanced. Labile Pb concentrations, extracted with either dilute HCl or EDTA, reached a maximum of 3,560 mg/kg compared to background values of <10 mg/kg. Additionally, 25% of the 169 contaminated samples analyzed had EDTA-extractable Pb enrichment ratios greater than or equal to 11.5, where a value of 1 separates uncontaminated from contaminated media. Given the proximity of most samples to roadways it is reasonable to conclude that automotive emissions plus vehicle wear were the primary contributors of trace metals to the roadside system. These data are discussed in context with previous work on the fluvial bed sediments in this watershed in an attempt to examine the potential linkage with the biological accumulation of Pb in fish from Manoa watershed.