河川底質の水銀汚染について １ 水門川底質の水銀汚染

Abstract

The wastewater of a chemical plant manufacturing acetaldehyde with mercurial catalyst had been emitted into the Suimon River in Gifu Prefecture. Monitoring surveys were made by measuring total mercury in bottom sediments from 124 sites in the Suimon River and the relevant rivers. The highest level, 180μg/g of mercury was detected at the site close to the outfall of the chemical plant and the mercury level ranged from the order of 10 to 102μg/g at the sites downstream, whereas they represented the order of 10-1to 100μg/g at the sites upstream. Therefore, the plant was proved to have been the source of mercury pollution of bottom sediments. The mercury pollution apperared to extend to the Makita River but not to the Ibi River. From the results of the survey of the horizontal distribution of mercury concentrations in sediments at 14 sites, it was found that the coefficient of variation of mercury concentrations in sediments from varied positions at a site reached 81.8% on the average, and mercury concentrations were generally lower in the centre of the channel but increased towards the shore. From the results of vertical distribution of mercury concentrations, a fairly regular relationship was obtained between depths of sampling positions and mercury concentrations. However, at some sites the relationship was observed to be inverse.