Heavy Metal Anomalies in Coastal Sediments of O'ahu, Hawai'i

Abstract

Interelement ratios to Cr in surface samples of coastal sediments and watershed soils of Oah'u, Hawai'i, show widespread, anomalous concentrations of Pb, Cd, and Hg when compared with basalt, the ubiquitous rock type. Enrichments of these heavy metals are especially pronounced in the carbonate sands of Kahana, Maunalua, and Mamala Bays, where enrichment factors for Pb, Cd, and Hg range from 84 to 240, 67 to 180, and 43 to 72, respectively, based on samples collected in the early 1970s. Lesser enrichments of Cu, Zn, and Ni generally parallel those of Pb, Cd, and Hg in highly contaminated areas at Pearl and Honolulu Harbors, and in cultivated watershed soils. Estimated deposition rates for Pb, Cd, and Hg from three major local source categories-motor vehicle, agriculture, and volcanic-indicate that motor vehicles are by far the largest source of Pb enrichments in O'ahu soils and sediments. Widespread mercury deposition is apparently dominated by local volcanic sources, whereas Cd deposition is more evenly dispersed among the three major sources. The estimated Pb and Cd deposition rates are in reasonable agreement with their observed sediment and soil burdens in the early 1970s. The estimated Hg deposition rates are higher than necessary to explain the observed burdens for this metal, possibly as a result of soil leaching, postdepositional volatility, or Hg uptake and re-emission by biota.