Abstract
The seasonal and long-term changes of MBAS in rivers and coastal waters in Hyogo Pref. were statistically analyzed with the monitoring data in the last 15 years.
In the river water, high concentrations (1 mg·l-1≤) of MBAS were observed at least once in 58% of overall monitoring stations. Many smaller rivers in Hanshin District, where the population and the industry were intense, were always polluted with anionic surfactants. However, gradual decreases in MBAS were observed by the degree greater than those of BOD in over 70% of the stations during the monitoring period. As to the seasonal changes, MBAS concentrations were higher in the cold season (Jan.-Mar. and Oct.-Dec.) and lower in the warm season (Apr.-Sep.) in 60% of the stations.
The causes of the long-term change and the seasonal change are presumed to be the diffusion of sewerage system in various areas and the active biodegradation of MBAS under higher water temperature, respectively.
In the coastal waters, long-term changes of MBAS were similar to those of the river water, while seasonal changes observed were different.
