Spatial Distributions of Dioxins and Sources in Sediment in Tokyo Bay

To reveal the spatial distribution of dioxins(PCDD/Fs and Co-PCB) in sediment in Tokyo Bay, field observations were conducted. The dioxins concentrations were analyzed at 22 sites in the whole bay region, including Chiba Port and an area near Ichihara anchorage, where high levels dioxins contamination had been observed. The characteristics of the specific congeners and TEQ were determined by combining our field observation results with existing data. The highest levels of TEQ were found near Ichihara anchorage, and levels gradually decreased towards the center of the Bay. The distribution of l,2,3,4,6,7,8-H7CDD was similar to that of TEQ. The concentration of l,3,6,8-T4CDD was the highest around an anchorage in Chiba Port, and l,3,6,8-T4CDD seemed to spread throughout the central region of the Bay. These result suggest that CNP contribution from land was small. The concentration of 2,3,4,7,8-P5CDF was the highest in the central region. On the other hand, the concentration of Co-PCB was the highest around Tokyo Port. The distributions of isomer ratio ( 1,2,3,4,6,7,8-H7CDD/1,2,3,4,6,7,9-H7CDD ) suggests that the source which contaminated sediment in Ichihara anchorage, affected sediment in Tokyo Bay.