WATER POLLUTION AND RESTORATION IN OSAKA BAY; HISTORICAL REVIEW AND SCIENTIFIC EVALUAION OF POLICIES OF AREA-WIDE TOTAL POLLUTANT LOAD CONTROL

During the period from 1960s to mid-1970s, problems of water pollution became more widely and severe with rapid economic growth in Japan. A system of Area-wide Total Pollutant Load Control has been established to restrict the quantity of organic pollutants discharged from land areas. COD was used as an indicator and reduction target. In the present study, an aquatic ecosystem model was applied to evaluate the effects of such control on the water quality conservation in Osaka Bay from 1950 to 2020. The results suggest that the load control should be expanded to include not only COD but nitrogen and phosphorus as well, because both nutrients cause internal production of COD.