Road-runoff metal concentrations in Toledo, Ohio, and their relation to average daily traffic and age of pavement overlay

Road runoff can contain metal concentrations and sampling of it can be expensive if auto-samplers are used. In this study, an inexpensive storm water sampling apparatus was developed and used for collecting the road runoff at eleven different sites in Toledo area. Sites were selected with the purpose of evaluating the effects of average daily traffic (ADT) and the age of pavement overlay on road runoff metal concentrations. Ag, As, Cd, and Mo concentrations were primarily below detection limit. Ba, Mn, Ni, Cu, Pb, and Zn were observed in higher concentrations but lower than <800 μg/L. Mg, Al, Fe, K, Na, and Ca were observed in mg/L levels, much higher concentrations. ADT was positively correlated with runoff concentrations of K, Mn, Pb and Zn. The source of Ca, Mg, and Mn appeared to be the asphalt pavement surface; with time, as the pavement aged, these sources appeared to be depleted as observed by lower runoff concentrations in older pavements.