FISH FULL LIFE-CYCLE TESTING FOR THE WEAK ESTROGEN 4-TERT-PENTYLPHENOL ON MEDAKA (ORYZIAS LATIPES)

摘要

We studied the chronic effects of 4-tert-pentylphenol (4-PP) on reproductive status of medaka (Oryzias latipes) over two generations under continuous exposure, with the goal of verifying the applicability of the fish full life-cycle test (FFLC) for this weak estrogen with this species. The exposure of parental (F_0) medaka to 4-PP was begun on embryos within 12 h after fertilization and continued for up to 101 d, with monitoring of embryological development, hatching, posthatch survival, growth, sexual differentiation, reproduction, and hepatic vitellogenin (VTG) levels under flow-through exposure to 4-PP at mean measured concentrations of 51.1, 100, 224, 402, and 931 μg/L. Eggs (F_1) spawned from the F_0 fish at 99, 100, and 101 d after hatch also were examined for hatchability, survival after hatching, growth, sexual differentiation, and hepatic VTG levels, until 61 d after hatch. In the FFLC with the F_0 medaka, the lowest-observed-effect concentration (LOEC) of 4-PP for lethal and sublethal toxicity (as shown by growth inhibition) was 931 μg/L. The LOECs for estrogenic effects (as shown by abnormal sexual differentiation and VTG induction) were 224 and ≤51.1 μg/L, respectively, and the LOEC for reproductive impairment was 224 μg/L. Therefore, the effective concentrations of 4-PP for abnormal sexual differentiation and reproductive impairment were about four times lower than those for lethal and sublethal toxicity. In the F_1 medaka, the LOECs for sublethal toxicity and estrogenic effects were 224 and ≤ 51.1 μg/L, respectively. This finding suggests that the continuous exposure to 4-PP over two generations induced these adverse effects at lower concentrations in the F_1 generation than those in the F_0 generation. Thus, 4-PP has estrogenic effects that reduce the reproductive potential of medaka. The results indicate that the FFLC with medaka is applicable to the evaluation of weak estrogens.