Variation in total and extractable elements with distance from roads in anurban watershed, Honolulu, Hawaii

Roads play a major role in transporting sediment associated nonpoint source pollutants to urban stream networks via storm drains. In urban areas the r elationship of erodible soil to roads may be of critical importance in cont rolling metal contributions to roads. Two 50-m transects (Park and School) were investigated perpendicular to roads in Manoa basin, Oahu, Hawaii. Conc entrations of nine elements were compared to background control soil locati ons and to five supplemental samples from nearby recreational parks. Sedime nt from curbside areas of roads (road deposited sediment) was collected as the starting point of each transect, and subsequently soil was sampled from two depths (0-2.5 cm and 7.5-10.0 cm) along the transects. Total and 0.5 M HCl extractable concentrations were determined for aluminum (Al), calcium (Ca), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), l ead (Pb) and zinc (Zn) using either inductively coupled plasma-atomic emiss ion spectroscopy (ICP-AES) or flame atomic emission spectroscopy (FAAS). Ca , Cu, Pb and Zn exhibited anthropogenic enhancement, with Pb and Zn having the greatest enrichment in road sediment followed by locations nearest the road. Copper displayed a narrower band of contamination than either Pb or Z n, and this may reflect larger aerosol associations and more rapid fall vel ocities. Lead and Zn exhibited substantial decay in concentration at 50 m c ompared to the road sediment, but enrichment was still apparent. The positi oning of a band of soil between the road-curb area and the sidewalk for the Park transect facilitated deposition and storage of trace metals, and with subsequent erosion by splash or concentrated flow this area can account fo r continued transport of contaminated sediment to adjacent road surfaces. O n the other hand the School transect had no soil directly beside the road, and the nearest sample from the road (5 m) displayed enrichment but substan tially lower than the Park transect. These preliminary data suggest that re mobilization of soil stored metals in close proximity to roads can signific antly prolong the environmental contamination of urban road systems and eve ntually stream sediments.