LAS in urban rivers and factors contributing to reduction of their concentrations.

LC/MS analysis with improved SPE preparation was applied to determine trace amounts of LAS in river waters. By using this procedure, the distribution of LAS was investigated and compared with the previous concentration level measured by HPLC in the Akashi River flowing through urbanized coastal areas in Hyogo Prefecture, western Japan. Detected LAS were in the range of 0.6-11 microg/L and considerably lower than those in 1985. This indicated that LAS concentration levels reduced to 1/10 and below during the past 18 years. From the model analysis, major factors contributing to the reduction of their concentrations were estimated to be the sewerage development and the decrease of consumption of anionic surfactants. Statistical analysis of MBAS monitoring data suggested that over 90% of sewerage diffusion rate was needed in order to reduce LAS to the concentration level of the order of 10 microg/L in river waters.