Geochemical Assessment of Trace Metal Distribution and Contamination in the Surface Sediments of the Coast of Okinawa Island, Japan

Abstract

In this study, sediment samples were collected from the Awase tidal, the Minamigusuku, and Nakagusuku areas located in the Okinawa Island. The collected samples were analyzed using X-ray fluorescence to determine their geochemical compositions and distribution, and to assess the sediment quality in the study areas. Contamination factor (CF), geoaccumulation index (Igeo), and the United State Environmental Protection Agency Sediment Quality Guideline (US EPA SQG) were used to assess the sediment quality. The results show that the highest average concentrations of As (11mg/kg), Pb (8 mg/kg), Zn (19 mg/kg), Cu (6 mg/kg), and Cr (14mg/kg) occurred in the Minamigusuku area. The CF and Igeo values, and the US EPA SQG indicate that among the selected trace metals only As displays significant values in the study areas. The CF values of As in the Minamigusuku area show moderate enrichment, and in this same area, the Igeo values of As present significant values, ranging from moderate to considerable contaminations, implying a possible effect on the biota in this location. Compared to the US EPA SQG, the Awase tidal flat and Nakagusuku areas are moderately polluted, whereas Minamigusuku is heavily polluted, suggesting that As may possible impact the biota in these areas. Consequently, for a better sustainable development of the coast of  Okinawa Island , a regular monitoring and assessment of study areas, particularly the Minamigusuku area, is necessary to determine over time the concentration of As.