OFF-FLAVOR PROBLEM IN DRINKING-WATER OF TOKYO ARISING FROM THE OCCURRENCE OF MUSTY ODOR IN A DOWNSTREAM TRIBUTARY

The Misato Purification Plant, Waterworks Bureau of Tokyo Metropolitan Government in 1992 encountered an off-flavor problem due to the forma tion of 2-methylisoborneol (MIB) in a small tributary. This tributary had become polluted by rapid urbanization of the basin, However, iris situated at a point lower than the Plant and does not discharge direct ly into the main river. MIB produced in the downstream tributary was t ransported by a back current and via a Conveyance Pipe to the main riv er. The causative blue-green algae in the tributary water was determin ed through chemical and biological analysis of field samples as well a s cultured materials. MIB production by one species of Oscillatoria is olated from the field samples was demonstrated. The strong MIB product ion potential of this species was also shown by a comparison of MIB pr oduction per unit length of trichome (16 pg/500 mu m) between this and other species reported previously. It was found that the presence of only one filament of this species in 1 ml of water could result in MIS levels above the threshold concentration of MIS for Japanese people. Results of this study revealed the importance of monitoring causative organisms and hydraulic conditions in tributary rivers.