Multi-element analysis of road-deposited sediment in an urban drainage basin, Honolulu, Hawaii

Abstract

Road-deposited sediment (RDS) and its associated contaminant load play a critical role in degrading receiving water bodies. Few quantitative multi-element RDS studies exist, and there are none from Hawaii. This lack of baseline data combined with concerns with high concentrations of Pb and Cu in fish and enrichment of Cu, Pb and Zn in bed sediments from Manoa Stream, Hawaii, lead to a detailed characterization of RDSs in Manoa basin. Data for a total analysis of 23 elements using inductively coupled plasma atomic-emission spectrometry and instrumental neutron activation analysis and 16 elements using a 0.5 M HCl partial leach are presented for RDSs and background soils. Concentration data, comparisons with environmental guidelines, and concentration enrichment ratios (CERs) all indicate that RDS in Manoa has a significant degree of anthropogenic pollution. The most environmentally important elements were Pb, Sb and Zn. Concentrations of these elements, primarily vehicle contributed, compare favorably with those from other studies of RDS. The high mean concentration of Pb (151 mg/kg) compared to background soils (13 mg/kg) indicates remobilization of Pb previously stored in soils and transported to road surfaces by water erosion processes. The higher Pb CERTotal in RDSs compared to bed sediments from Manoa Stream suggests a potential link via ubiquitous storm drains and subsequent dilution with less contaminated fluvial sediments. Data from the HCl leach also support Pb and Zn as having significant anthropogenic signals, and Cu having a moderate signal. These data indicate that RDSs in Manoa basin are generally contaminated with certain potentially toxic elements and the legacy of past use of leaded gasoline is still a concern in this urban drainage system.