SEASONAL-VARIATIONS AND MODES OF RIVERINE INPUT OF ORGANIC POLLUTANTS TO THE COASTAL ZONE .1. FLUX OF DETERGENT-DERIVED POLLUTANTS TO TOKYO BAY

In order to discuss seasonal variations and modes of riverine input of organic pollutants to the coastal zone, linear alkylbenzenesulfonates (LAS) and linear alkylbenzenes (LABs) were determined for the Tamagawa River water at 2-week intervals for 2 years. The sampling site, Chofu Dam, is located at the boundary between freshwater and brackish zones. LAS flux was ca. 5 times higher in winter than in summer. LAS with longer homologues and external isomers were more depleted in summer. The LAB isomer distribution also showed a clear seasonal trend in that external isomers were more depleted m summer, while LAB flux had a small seasonal variation. These seasonal variations are due to higher microbial degradation activity of in-stream LAS and LABs at higher water temperatures in summer months. A continuous supply of LAS to the estuary was relatively more important (96 % of the annual supply) than an intermittent supply. However, a major portion of the LABs (67 % of the annual supply) were intermittently transported to the coastal zone by flush during/after rainfall. Despite the LABs' highly hydrophobic nature, 10-80 % of total LABs were transported as the dissolved form. This may be due to association of LABs with colloidal material and/or solubilization by surfactants. The annual suspended SIGMALAB flux to Tokyo Bay via the Tamagawa River is estimated at 110 kg/yr, which comprises 6.4 % of the SIGMALABs accumulated in Tokyo Bay sediment. Annual SIGMALAS flux is estimated at 320 ton/yr. This is much greater than the amount of SIGMALAS accumulated in the bay sediment (0.4 ton/yr), indicating that more than 99.9 % of the LAS are degraded in the estuary and the bay.