Distribution, Geochemical Speciation, and Bioavailable Potencies of Cadmium, Copper, Lead, and Zinc in Sediments from Urban Coastal Environment in Osaka Bay, Japan

Due to proximity to the urban and industrial areas, coastal environments of the Osaka Bay have been continuously polluted with the human activities. Coastal sediments are known as large pool of contaminants including heavy metals. The Osaka Bay is no exception. However, recent information regarding the distributions, geochemical speciations, and risk evaluations of metals is limited for coastal sediments in the Bay. Therefore, we investigated the distributions, geochemical speciations, bioavailabilities, and conducted risk evaluations of the heavy metals, such as cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in sediments collected from 25 sites of the urban coastal environment of Osaka Bay, Japan. We observed high concentrations of Zn (76–967 mg/kg dry weight; DW) followed by Cu (not detected; ND-399 mg/kg DW), Pb (ND-73 mg/kg DW), and Cd (0.2–2.9 mg/kg DW). A considerable fraction of Cd was exchangeable (ND-0.4 mg/kg DW) and carbonate-bound (0.03–0.4 mg/kg DW). Cu occurred predominantly in the organic material-bound fraction (ND-348 mg/kg DW). Both Pb and Zn occurred predominantly in the Fe-Mn oxide fraction, with concentration ranges of ND-41 mg/kg DW and 24–277 mg/kg DW, respectively. Comparison with the effect range low (ERL) and effect range median (ERM) revealed that Cd, Cu, and Zn contribute potential biological toxicities to the sediments of Osaka Bay. High bioavailable concentrations of Cd and Zn may have ecotoxicological significance, because these metals are potentially highly available, especially to the benthic organisms.