Abstract
An economical and simple method of evaluating the impact of water discharged into natural ecosystems was examined using an ecosystem model. An ecosystem model containing medaka and water grass (Egeria densa) was prepared. The three water types used were underground water polluted with volatile organic compounds (VOCs) including trichloroethylene, and diluted with tap water, effluent water that was treated with a biological treatment system; and tap water. Spawning and hatching, mainained hepato-somatic index (HSI), gonac somatic index (GSI) and concentration of vitellogenin (VTG) were monitored. The polluted water, the spawning and hatching of medaka were normal, but the growth of the water grass was restricted although trichloroethylene had been volatilized by pumping air through the water. In contrast, fish that were held in aquarium that contained treated water appeared almost the same as fish bred in tap water, exhibiting no abnormalities in spawning, hatching, or growth. In addition, water grass did not degenerate in such an environment. The areas for improvement of this evaluation method were identified. It is not yet known which types of water are the best controls for the tests.
