抄録
The toxic effects of cadmium, zinc, copper, and nickel ions and their pyrithione complexes on Daphnia magna embryos and juveniles were evaluated. Four- to 8-hourold embryos were obtained from the mother’s brood chamber and immediately exposed to various concentrations of each test substance for 120 hours. Embryonic toxicity was determined by evaluating the inhibition of hatching and the immobilization of the embryos after 72, 96, and 120 hours. Juvenile D. magna（less than 24 hours after release by the mother）were also exposed to the test substances for 48 hours. The results of all tests were analyzed and the median effective concentration（EC50）of each test substance was calculated. Cadmium ion exhibited significant toxicity during embryonic development, causing arrested development and immobilization of embryos exposed to a Cd2+ concentration of 0.2×10-7 mol/L（2.2 μg/L）. The 48-hour EC50 value for the immobilization of juveniles was about 10-fold greater than the 120-hour EC50 value for inhibited hatching and immobilization of embryos. Cadmium pyrithione complex had a greater effect on embryonic development than cadmium ion. Analyses of the toxic effects of other metals indicated that D. magna embryos are more sensitive to heavy metals than are juveniles. The 120-hour EC50 values for the heavy metal ions examined were similar to the values at the endpoints of chronic 21-day reproduction tests reported in the literature. These observations suggest that the embryonic developmental test allows for rapid and sensitive early life-stage determination of heavy metal toxicity and is thus an alternative to the 21-day reproduction test.
