| To establish the whole effluent toxicity (WET) test specific to evaluation of sewage effluent, we examined the sensitivities of Zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). In the test of sensitivities to three chemicals (nickel chloride, ammonium chloride, and sodium hypochlorite), differences of NOEC values by these two fishes were the extents of 0.5-2 fold. These results showed that the sensitivities to chemicals were similar in D. rerio and O. latipes. In the WET test for the sewage effluent, NOEC values of the influent were the same (40%) as D. rerio and O. latipes. The NOEC value was over 80% in the test of second effluent using D. rerio. On the other hand, the NOEC value of secondary effluent could not be obtained from the test by O. latipes, because surface of eggs allowed microorganisms to grow in water samples diluted in 20 and 40%. From these reasons, we suggest that D. rerio is recommended to be used to evaluate wastewater in the WET assay. |
