The pollution level of the Tsurumi River flowing into Tokyo Bay was studied longitudinally using river sediment extracts in an assay system based on the arylhydrocarbon receptor (AhR)-dependent induction of 7-ethoxycoumarin O-deethylase (ECOD) activity in HepG2 cells. The sampling points of river sediment were as follows: Namamugi, Kami-Sueyoshi, Tsunashima, Shin-Yokohama A and B (downstream and upstream, respectively, from the former open-air industrial waste incineration site), Kozukue and Nakayama (Fig. 1). ECOD activity was induced to different extents in all samples tested. Namamugi, located in the middle of Keihin Industrial District, was considered to be the most polluted, followed by Shin-Yokohama A and Tsunashima. Results from these samples showed reverse U-shaped dose-response curves in terms of ECOD activity as well as 3-methylcholantrene (3-MC) although the expression of CYP1A1 mRNA in HepG2 cells remained roughly constant at higher concentrations as in the case of 3-MC, thus implying post-transcriptional suppression.

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