Abstract
The authors comparatively studied effects of γ-rays and some heavy metal treatments on mobility of water flea Daphnia magna according to the OECD Guideline for Testing of Chemicals, which is generally used for ecotoxicity evaluation of chemicals. The 50% effect dose at 24 hours after γ-irradiation (ED50/24h) was 1 600 Gy. The 50% effect concentrations following 24 hours exposure for manganese, nickel and copper (EC50/24h) were 990, 180 and 3.3 μM, respectively. The Gy-equivalent factors (=ED50/24h/EC50/24h) were therefore calculated as 1.6, 8.9 and 480 for manganese, nickel and copper, respectively. These factors indicate that toxicity of these metals to D. magna can be ranked in an order of Mn<Ni<Cu. This toxicity rank shows a similar trend to that evaluated previously in the experimental model ecosystem (microcosm) consisting of three species of aquatic microorganisms. However, there was a noteworthy difference in the toxicity ranks obtained from the D. magna immobilization test and the microcosm test, suggesting that ecotoxicity ranking should be carried out by integrated evaluation on the basis of various ecotoxicity tests.
