Distribution and Variation of 1,4-Dioxane in Water from Rivers in Niigata Including the Shinano River

The distribution of 1,4-dioxane in the waters from 27 sites in 12 rivers including the Shinano River, the longest river in Japan, was investigated in 2002. 1,4-Dioxane was detected in concentrations ranging from 0.02 to 0.49 μg/L. The monthly variations in the 1,4-dioxane concentrations at 6 sites along the Shinano River showed mutually different patterns, and the concentrations did not correlate with the concentrations of the biochemical oxygen demand and the suspended substances. The annual mean concentrations were from 0.02 μg/L at sites located in the middle reaches to 0.11 μg/L at the river mouth. The 1,4-dioxane concentration in the Shinano River has shown a downward trend from 1989 to 2003.