Polychlorobiphenyis (PCBs) in sediments of Tokyo Bay,Japan

Sediment cores were collected from five sites in Tokyo Bay. The sediment age was estimated by the²¹⁰Pb method and the polychlorobiphenyls (PCBs)(2,5,2,4,5 — pentachlorobiphenyl,3,4,2,4, 5-pentachlorobiphenyl, 3,4,2,3,4-pentachlorobiphenyl, 2,3,6,2,3,6-hexachlorobiphenyl, 2,4, 5,2,4,5-hexachlorobiphenyl, and 2,4,5,2,3,4, 5-heptachlorobiphenyl) profiles in the sediments were determined quantitatively by gas chromatography. With respect to the horizontal distribution of PCBs, the levels were highest off Tokyo and Kawasaki, the inner western part of the bay off the mouths of the Tama and Arakawa Rivers, and declined in the direction of the eastern and southern parts of the bay. It was assumed that most of the PCBs supplied to the bay from the adjacent rivers and the industrial zones along the western coast were coprecipitated with suspended particles near the river mouths and the western coast, while PCBs adsorbed by fine particles are carried throughout the bay by the current. The accumulation rate of PCBs in Tokyo Bay sediments gradually increased, starting about 1936, and reached a maximum value in 1972 and declined moderately thereafter. The time-dependent changes in the quantity released into the environment were estimated from the amount of PCBs manufactured and used. The accumulation rate of PCBs in Tokyo Bay sediments was then compared with the estimated rate of release into the environment.