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The extent of pollution in the rivers flowing into Tokyo Bay was studied comparatively 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 on the Tsurumi River, Rokugo on the Tama River, Hirai, Senjyu and Funado on the Ara River, Baraki on the Edo River, and Makuhari on the Hanami River (Fig. 1). The Tsurumi River (Namamugi) located in the middle of Keihin Industrial District was considered most polluted, followed by the Ara River (Hirai). The river sediment collected at Baraki on the Edo River was least polluted. The extracts of highly polluted river sediments sampled at Namamugi and Hirai exhibited a reverse U-shaped dose-response curve, for which polycyclic aromatic hydrocarbons (PAHs) might be mainly responsible, in a range of non-toxic concentrations. The pollution of river sediment collected at Namamugi was roughly estimated to be 2 to 20 µg as PAHs/g sediment by consulting the data of Nakama et al.1) and 0.2 to 2 µg as PAHs/g was assigned to the river sediment of Hirai.

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