Urban highway runoff samples collected from four rainfall drains were analyzed for heavy metals and polycyclic aromatic hydrocarbons (PAHs). The concentrations of constituents varied widely during the history of each storm and appeared to be highest in the first runoff water. Results showed that iron and aluminum were the principal constituents of particulates. Cadmium, chromium, copper, manganese, lead and zinc were mainly particulate-bound while nickel was mainly in dissolved form. The higher molecular weight PAHs were more associated with suspended solids in the runoff. Predominant PAHs-phenanthrene, fluoranthene and pyrene-comprised about 50% of fifteen quantified PAHs constituents in each sample. In the events where peak flush occurred during the initial phase, more than half the total load flowed out during the initial phase of runoff flow. In this case, initial runoff water treatment was believed to be effective. In results from Ames assay, mutagenicity was appreciably associated with PAHs in the particulate fraction of runoff water. The dissolved fraction also showed positive mutagenic response by unknown soluble aromatic compounds.
Many studies have identified the first flush phenomenon and runoff characteristics. The purpose of this study is to elucidate which parameters influence the runoff pollutant loads. Eight runoff events during the period from May 1999 to September 2000 were investigated. From the dimensionless cumulative analysis, it was suggested that particulate substances such as suspended solids (SS), iron and total phosphorus (T-P) were inclined to be washed off in heavier rainfall condition. The cumulative curves of particulate constituents were appreciably variable in slope, while those of dissolved were approximately constant. Accordingly it was indicated that dissolved load was discharged regardless of rainfall conditions. Event mean runoff intensity and cumulative runoff height showed significant correlation with the cumulative runoff load of the constituents except for total nitrogen (T-N). On the other hand, antecedent dry weather period (ADWP) and traffic flow volume during ADWP did not show correlation with the cumulative runoff loads. Only T-N load showed correlation with those factors, consequently it was suggested that vehicular exhausts affected nitrogen load on the surface of urban highway.
Lead isotopic analyses of road runoff and airborne particulate matter have been carried out to elucidate sources of lead pollution at urban and suburban sites. While lead is often observed in road runoff in suspended form, suspended particle size had no relation to the lead isotopic distribution, as a result of comparison between runoff samples with total suspended solids and those with minute particles passed through a 75 microm sieve. Lead isotope ratios in airborne particulate matter in urban areas fell within a wider range than those in road runoff. Since there was little difference of the ratios between a heavy traffic-flow site and residential sites, airborne lead derived from vehicle exhaust was found to make little contribution to the contamination of road runoff. On the other hand, the ratios in road runoff at a suburban site showed the same range as those at an urban site. Lead in road runoff was therefore suggested to be produced on site by traffic related substances, such as tire wear, other than vehicle exhaust.
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