Abstract
The fish death accident occurred in Miyagi Prefecture in the winter of 1999/2000. It was considered that urea compound deicer used on the road flowed into the stream, and microorganisms in the fluffy mud of the site decomposed urea, then the strong toxicity, which was caused by the synergism of ammonia and carbonic acid, led to the fish death.
We tested the possibility of decomposing urea compound deicer by the fluffy mud in the stream where accident occurred. We carried out experiments of decomposition of the urea solution using the fluffy mud samples of the accident spot of the stream at various temperatures. The experimental results showed that the fluffy mud strongly decomposed urea into ammonia and carbonic acid even at the low temperature, and one fungus was recognized in the mud : This was identified as Trichosporon cutaneum by the biological and chemical tests. None have reported that this fungus decomposes urea in the river, the natural water world.
