Abstract
The long-term and seasonal variations of anionic surfactants in rivers of Kinki Region were statistically evaluated by using MBAS (methylene blue active substances) monitoring data during 1972-1988.
High concentrations over 1 mg·l-1 as the average for the observation period were found in 18% of the 440 monitoring stations, and 30% of the total stations indicated significant long-term variations of MBAS concentration which was charaterized by the decrease at high concentration points. The relation between the ratio of the population served by public sewerage and MBAS concentration suggests that the diffusion above 80% is necessary in decreasing to MBAS level below 0.5 mg·l-1 in urban rivers.
In many cases, MBAS correlated positively with BOD and negatively with water temperature at different stations and in different prefectures, and the contributions over 0.5 were obtained in multiple regression analysis with MBAS as criterion variable and BOD and water temperature as explanatory variables. These suggest that the two paramerers explain predominantly the variations of MBAS concentration in river waters.
