In 1969 a musty odor was first found in the southern basin of Lake Biwa. Since then we have been investigating the causes of the problem. In the 1970's musty odor problems commonly occurred from May to early June due to the metabolites produced by Phormidiumtenue. However, the problem which took place in the summer of 1981 was found to be caused by an algal bloom of Anabaenamacrospora.

The analyses of the water taken in the lake as well as of the laboratory cultures of the blue-green algae led to the conclusion that 2-methylisoborneol is produced by Phormidiumtenue, whereas geosmin by Anabaenamacrospora.

Purge and trap concentration followed by mass fragmentography was developed and applied as a measurement method for these two odorous compounds. The method was found to be rapid, reproducible and sensitive enough to detect them at a nanogram per liter concentration level or beneath their threshold odors, requiring only a small sample (100 ml).

Slow sand filtration was found to be effective in removing odor, where the odorous compounds were reduced to less than 10 ng/l in the effluents.

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