A first look at platinum in road-deposited sediments and roadside soils, Honolulu, Oahu, Hawaii

Platinum (Pt) has become globally distributed by anthropogenic inputs, primarily from automobile emissions resulting from degradation of catalytic converters. These inputs are greatest in urban areas, with the major sinks being road sediments and roadside soils. Limited data are available on the distribution of Pt in the environment. No data for Pt in road-deposited sediments are presently available from the United States, and only a few studies offer a limited perspective of Pt in urban soils in the United States. This investigation represents the first study in the United States to characterize Pt concentrations and enrichment ratios in both road sediments and roadside soils in an urban (nonindustrialized) basin in Honolulu, Hawaii. Two independent analytical techniques-cathodic stripping voltammetry and lead-fire assay followed by ICP-AES-were used to quantify Pt in environmental media. Data from 10 road sediments confirm Pt contamination, with a median concentration of 33 ng g(-1) and a range of 15-160 ng g(-1). Upper soil horizons in roadside areas also exhibited contamination, with a median Pt value of 14 ng g(-1) (range 2-160 ng g(-1)), but significantly lower than road sediments. Computation of robust enrichment ratios using baseline soil, geology, and tree bark data indicated that road sediments had a median Pt enrichment of 9 (range 4-46), upper soil horizons a median of 4, and lower horizons 1.1. The latter were not found to differ significantly from Pt baseline concentrations. However, several roadside sites exhibited significant enrichment with depth, which may indicate potential Pt mobility in this environment. These data support a substantial loading of Pt in the urban environment of Hawaii. Further work is required to characterize the distribution of other autocatalyst-associated noble metals palladium (Pd) and rhodium (Rh) in the environment.