Abstract
Distribution and levels of volatile organochlorines in the Yodo and the Yamatogawa river basins, the rivers in Osaka City and Osaka Bay in Japan were surveyed around 1990, and furthermore those results were compared with the previous study at the end of the 1970's before implementing any regulations. Around 1990, the levels of volatile organochlorines in the Yodo river basin were averaged as 0.36μg/l for chloroform (CF), 0.29μg/l for 1, 1, 1-trichloroethane (MC), 0.08μg/l for carbon tetrachloride (CTC), 0.23μg/l for trichloroethylene (TCE) and tetrachloroethylene (PCE) . Especially, TCE was rarely detected downstream of the Yodo River. Their levels in the rivers of Osaka City, at places directly receiving discharges from human activities, were higher by one order of magnitude compared with those in the Yodo river basin. In the Yamatogawa river basin, the levels of TCE and PCE were one-third of those in the Yodo river basin. In Osaka Bay, the levels of CF and MC were half, and those of TCE and PCE were one-tenth of the Yodo river basin. It was clear that the levels of volatile organochlorines were falling as being remote from urban areas. The levels of TCE and PCE have drastically decreased during the past decade, but the others remained at the same levels. At the end of 1970's, the levels of each volatile organochlorines in the mainstreams have fluctuated due to discharges from sources with high levels of organochlorines scattered around the basin. In contrast, around 1990 their distribution was unified. It may be due to the decrease in polluted sources by legislation. The order of levels in Osaka Bay, except for CF, was followed by that of the annual productions of organochlorines in the years of surveillance. CTC was almost the same level regardless of the years and the areas. In the rivers of Osaka City, TCE and MC were loaded from the usage of degreasing and PCE was as a result of dry cleaning. CF was mainly originated from water chlorination such as disinfection of sewage treatment plants.
