Toxicity testing of 2,3,7,8-tetrachlorodibenzo-p-dioxin in early-life stage of Japanese medaka: Optimization of conditions for assessing relative potencies of dioxin-like compounds

抄録

In order to develop an optimal method for the investigation of relative potencies of dioxin-like compounds using Japanese medaka, the present study conducted five independent early-life stage toxicity tests using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as the positive control. First, both short- and long-term effects of TCDD were examined to determine sensitive and highly reproducible endpoints. Then, the outcome and threshold of TCDD toxicities under different experimental conditions, e.g., exposure timing and duration, were compared to develop a cost-effective method. Finally, we decided to observe yolk sac/pericardial edema, hatching failure, and mortality of medaka embryos/larvae within a 28-d experimental period, after 6-h exposure to TCDD at 0-d post fertilization. We obtained the LC₅₀ values of TCDD at 28-d post fertilization based on its concentration in water (6.84 ng/L) or in egg (753 pg/g-egg), and the LC₅₀ values were comparable with those reported in the literature. Thus, in our future studies, relative toxic potencies of dioxin-like compounds will be tested using the method established in this study.