Historical trends of PCDD/Fs and CO-PCBs in a sediment core collected in Sendai Bay, Japan

The vertical distribution of dioxins in a sediment core was investigated to elucidate historical trends of dioxins discharged into Sendai Bay, Japan. The dioxin concentration was 410 pg/g dry weight (dw) in sediments deposited in the mid-1930s and 3870 pg/g dw in those deposited in the mid-1980s. Dioxin fluxes increased from the mid-1930s and then reached a maximum in the mid-1980s. 1,3,6,8-TeCDD+1,3,7,9-TeCDD, OCDD, and Co-PCB concentrations were 110, 140, and 26 pg/g dw, respectively, in mid-1930s sediments, and reached maximums of 1800, 1100, and 200 pg/g dw, respectively, in mid-1980s sediments. Shipments to Miyagi Prefecture of CNP and PCP products, the major sources of 1,3,6,8-TeCDD+1,3,7,9-TeCDD and OCDD, were highest in 1975 (4700 t) and 1970 (3100 t), respectively; and in Japan, the amount of PCBs, the major source of Co-PCB congeners, used was highest (11,100 t) in 1970. Thus, the period for which the maximum concentrations of 1,3,6,8+1,3,7,9-TeCDD, OCDD, and Co-PCBs were measured in the sediment core (mid-1980s) did not correspond to the time of maximum use of CNP, PCP, or PCB products, but lagged behind by more than 10 years. We attributed this time lag to the time required for the movement of dioxins from Miyagi Prefecture to Sendai Bay.