Abstract
This paper describes a study to characterize water quality problems in urbanized area in Tokyo, Japan. The toxicity of river water was measured at 37 sites in 29 rivers and streams by using two aquatic bioassays, Daphnia magna (Cladocera, Crustacea) acute immobilization test and the Microtox test. Measurement by the bioassays of the water samples showed persistence of toxicants in several river waters at acute level for D. magna and less toxicity for the marine bacteria Photobacterium phosphoreum (the Microtox test) . Determination of the water quality by chemical analysis revealed a wide range of contamination by pesticides, ammonia and anionic surfactant. Results indicate organophosphate insecticides to be predominantly responsible for the observed biological effects of river waters on D. magna. The insecticides concentrations in the river waters in Tokyo were substantial enough to cause a threat to the ecosystem. The use of daphnia assays has helped to focus attention on the use of pesticides in paddy field and other urbanized areas next to the rivers. The Microtox test results were inconsistent with the results of D. magna test, the pesticides concentration, or the BOD of water samples. The toxicant for the Microtox bacteria did not clarified.
