Vertical profile of polychlorinated dibenzo-p-dioxins, dibenzofurans, naphthalenes, biphenyls, polycyclic aromatic hydrocarbons, and alkylphenols in a sediment core from Tokyo Bay, Japan

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and nonylphenol (NP) were measured in a dated sediment core collected from Tokyo Bay, Japan, in order to Study the history of contaminant inputs and fluxes. Concentrations of organochlorine compounds measured in this study increased gradually from the beginning of the early 1900s, reached a maximum in the early 1980s, and decreased steadily until the 1990s. The profile of isomer/congener compositions of PCDDs/DFs and PCNs varied with depth, which suggested that the sources of input of these compounds varied at different periods. The possible changing sources of PCDDs/DFs and PCNs to the environment a rediscussed in the context of the concentration trends and congener-specific data. The composition of PCB congeners was uniform at the top 40 cm, which corresponded to the period of usage of technical PCB mixtures, suggesting that the major single source of PCBs in sediments was technical preparations. All of the above organochlorines were detected in sediment sections collected at 90 cm depth, which corresponded to the early 1900s, suggesting the occurrence of these compounds in pre-industrial sediments. The vertical profile of PAHs was similar to that found for organochlorines with the highest concentrations occurring in the early 1980s. The vertical profile of NP concentrations was different from those observed for restricted compounds such as PCBs and PAHs. NP concentrations were greater in surface sediments (0-12 cm) than those in subsurface sediments (12-30 cm). In general, the profile of residues of organic compounds reflected production and usage trends of the respective compounds, although there was a time lag of a few years between peak periods of usage and deposition in coastal sediments. Improvements in emission controls in the late 1980s and the early 1990s appear to have been effective in reducing the inputs of organic residues to the environment; however, the concentrations of several organochlorines in surface sediments are still greater than those found in sediments from the 1970s.