Title Mass Balance and Bioaccumulation of Major Dioxins in Sendai Bay
Authers Yutaka OKUMURA
Keywords dioxin flux, marine food web, aquatic organisms, chlorinated pesticides, Miyagi Prefecture
Citation Bull. Fish. Res. Agen. No.37, 1-64, 2013
“Dioxins”is the general term for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (Co-PCBs). Because dioxins are stable chemical compounds, dioxins released into the environment have remained for long periods. The dioxins carried from the terrestrial to the marine environment may affect marine organisms, and it is possible that fishery resources are diminished through the toxicity of dioxins. The aim of this study is to clarify the behavior of dioxins that are emitted from Miyagi Prefecture and enter Sendai Bay via rivers.
 First, Chapter 2 describes the properties of dioxins in Sendai Bay, and discusses the bioaccumulation of dioxins through the marine food web and the bioaccumulation of dioxins with respect to the body length of flatfish. The order of concentration of PCDD/Fs was Pacific oyster > Japanese anchovy ≒ marbled sole > Japanese flounder; the concentration in Japanese flounder, which is a higher-trophic-level consumer in the marine food web, was lower than that in shellfish (Pacific oyster) and Japanese anchovy, which are lower-trophic-level consumers. The order of concentration of Co-PCBs was Pacific oyster < Japanese anchovy ≒marbled sole < Japanese flounder; the concentrations in the higher-trophic-level consumers were higher than the concentrations in the lower-trophic-level consumers. Different PCDD/F congeners tended to bioaccumulate in different organisms. On the other hand, all species of Co-PCB congener tended to bioaccumulate in all organisms.
 The relationship between the concentrations of these dioxins and the body length of Japanese flounder was examined. The total PCDD and total PCDF concentrations did not correlate with body length (both r 2 < 0.1, both p > 0.05), whereas the total non-ortho PCB and total mono-ortho PCB (Co-PCBs) concentrations were significantly correlated (r 2 = 0.8, p < 0.05 and r 2 = 0.63, p < 0.05, respectively). The bioaccumulation properties of PCDD/Fs in Japanese flounder differed from those of Co-PCBs. Toxicity equivalency quotient (TEQ) values derived from the Co-PCBs made up 46.3-63.7% of the total TEQ value for all the dioxins. These results show that from the standpoint of risk management, non-ortho Co-PCBs are the most important of the dioxins in Japanese flounder.
 In Chapter 3, the vertical distribution of dioxins in a sediment core was investigated to elucidate historical trends of dioxins discharged into Sendai Bay. In the off Naruse sample, the dioxin concentration was 410 pg/g 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. While sedimentation rates of total dioxins in the off Ishinomaki sample were 161.2 pg g-1 year-1 during 1992-2002 and 172.6 pg g-1 year-1 during 1981-1992. Thus, the rate during 1992-2002 was slightly lower than that during 1981- 1992, and the dioxin sedimentation rate gradually decreased from the mid-1980s to the early 2000s.
 Chapter 4 describes the terrestrial sources of dioxins and their concentrations in rivers leading to Sendai Bay. The major dioxin congeners in the river water were 1, 3, 6, 8-TeCDD, 1, 3, 7, 9-TeCDD, and OCDD. Chemical mass balance model results suggested that chloronitrophen (CNP) and pentachlorophenol (PCP), which are impurities in chlorinated pesticides used in paddy fields, accounted for > 90% of PCDD/F contributions, and exhaust gases for < 10%. PCA results suggested that PCB products were the major sources of CoPCBs, although total Co-PCB concentrations were lower than total PCDD/F concentrations.
 Concentrations of 1, 3, 6, 8- and 1, 3, 7, 9-TeCDD and suspended solids in river water increased with increasing flow rates. During periods of high flow, dioxin concentrations may have increased because of resuspension of bottom sediments that had adsorbed dioxins. In major rivers, the relative magnitudes of the annual average of daily fluxes of 1, 3, 6, 8- and 1, 3, 7, 9-TeCDD were: Kyu-Kitakami River > Naruse River > Abukuma River > Natori River. The flux from the Kyu-Kitakami River to Sendai Bay accounted for 49% to 84% of the total flux from the four rivers. The annual fluxes of major dioxin congeners tended to depend on both the size of the land area covered by paddy fields in the river catchments and the discharge rates of the rivers.
 Finally, Chapter 5 presents estimates of the flux of major dioxin congeners from Miyagi Prefecture to Sendai Bay. Large quantities of dioxins from CNP and PCP sources were introduced into the terrestrial environment (30.7 t). As the rivers and drainage ditches acted as transport bottlenecks, their inflow from the terrestrial environment to Sendai Bay was limited (241 kg). The bulk of dioxins from CNP and PCP sources remained in the terrestrial environment. Almost all dioxins entering Sendai Bay (7.7 kg/y) either flowed out of the bay or settled to the bay bottom. The amount that bioaccumulated in marine organisms (3.2 g/y) was much less than the amount inflowing from the terrestrial environment to the bay (0.04 %). The major dioxin congeners from impurities in CNP and PCP have much lower toxicities and bioaccumulation rates in marine organisms than low-chlorine 2, 3, 7, 8-substituted PCDD/Fs such as 2, 3, 7, 8-TeCDD, which has an extremely high TEF. Therefore, although the influx of dioxins of CNP and PCP origin to Sendai Bay will continue in the future, their bioaccumulation in marine organisms in Sendai Bay will not be a serious problem for fisheries resources.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull37/37-01.pdf