FATE OF TOXIC CHEMICALS INFLOWED FROM WATERSHED IN COASTAL ENVIRONMENTS

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(1) Dynamics of dissolved organic matter in rivers, estuaries and coastal regionsThe dynamics of dissolved organic matter (DOC), e.g. production, decomposition, transformation, were discussed on the basis of the results obtained by the field surveys with chemical fractionation and biodegradation tests.(2) Photolysis of PAHs in ground surfacesSeasonal changes in the photolysis rates of suspended and deposited particles were measured, suggesting the importance of photolysis in the dynamics of PAHs (Polycyclic Aromatic Hydrocarbons) in watersheds.(3) Prediction of toxic chemicals in waters and sedimentsSimple models were proposed to predict the concentrations of toxic chemicals in waters and sediments, indicating fairly good predictability.(4) Dynamics of PAHs in Hiroshima Bay and its watershedAlmost all the deposited PAHs on the ground surfaces could be run off through rainfall. The predicted PAHs concentrations based on the dry deposition rates and river inflow rates were in good accordance with the observed ones. The accumulation of PAHs in the brain and the organs of generation was found for the fish captured in Hiroshima Bay. The risk due to PAHs was evaluated to be rather high for the ecosystem of Hiroshima Bay.