Sources of heavy metals and polycyclic aromatic hydrocarbons in urban stormwater runoff

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals were measured in road debris collecting in urban areas and in the suspended sediment (SS) component of runoff from two stormwater catchments in Dunedin, New Zealand. Levels in the road debris ranged from 119–527 Ag/g for lead, 50–464 Ag/g for copper, 241–1 325 Ag/g for zinc and 1.20–11.6 Ag/g for A16PAH. The SS from the largely rural catchment (20% urban) had similar concentrations to the road debris, indicating that this urban material was the main source of the contaminants measured in the stormwater. Similar PAH fingerprint profiles and isomer ratios indicative of dominant pyrogenic (combustion) sources were also found in these two groups of materials. The SS from the 100% urban catchment contained 2- to 6-fold higher concentrations of metals and 10-fold greater levels of A16PAH. The higher levels of lead and copper were probably a result of industrial land uses in this catchment, while the additional zinc was linked to an abundance of zinc-galvanised roofing iron in the catchment’s residential suburbs. The PAH profiles and isomer ratios were different for this urban catchment and suggested that a disused gasworks was contributing PAHs to the stormwater runoff.