title: Life-cycle toxicity of 4-nonylphenol to medaka (Oryzias latipes).
abstract: We studied the chronic effects of 4-nonylphenol (4-NP) on reproductive status of medaka (Oryzias latipes) over two generations of continuous exposure. The exposure study of the parental (F0) medaka was begun on embryos within 24 h postfertilization and continued with monitoring through embryological development, hatching, posthatch survival, growth, sexual differentiation, and reproduction under flow-through exposures to mean measured 4-NP concentrations of 4.2, 8.2, 17.7, 51.5, and 183 microg/L for up to 104 d. Eggs spawned from the F0 fish at 102 and 103 d posthatch were also examined for hatchability, survival after hatching, growth, and sexual differentiation until 60 d posthatch. The 183-microg/L treatment significantly reduced the embryo survival and swim-up success of the F0 fish. The cumulative mortality after swim-up of the F0 fish exposed to 17.7 and 51.5 microg/L were significantly higher than the control mortality. No concentration-related effect of 4-NP was observed on the growth of surviving F0 fish at 60 d posthatch. However, the sex ratio estimated from the appearance of their secondary sex characteristics was skewed toward female in the 51.5-microg/L treatment. Additionally, gonadal histology showed that 20% of the fish in the 17.7-microg/L treatment and 40% in the 51.5-microg/L treatment had testis-ova, indicating that 4-NP affects the gonadal development and survival of medaka at similar concentrations in juveniles. The sex ratio of the F0 fish in the 51.5-microg/L treatment was completely skewed toward female; subsequently, the effects on fecundity and fertility in this generation were monitored at mean measured concentrations of 4.2, 8.2, and 17.7 microg/L from 71 to 103 d posthatch. Fecundity was unaffected by any of the treatments examined. The mean fertility in the 17.7-microg/L treatment was reduced to 76% of that in the controls, although no statistically significant differences were determined. Overall, these results indicate that the lowest-observed-effect concentration (LOEC) and no-observed-effect concentration (NOEC) of 4-NP through the life cycle of the F0 medaka were 17.7 and 8.2 microg/L, respectively. In the F1 medaka, no significant effects were observed on hatching success, posthatch mortality, or growth, but sexual differentiation at 60 d posthatch was affected. Induction of testis-ova in the gonads of the F1 fish was observed in both the 8.2- and the 17.7-microg/L concentrations. The results indicate that 4-NP can have significant effects on reproductive potential of medaka at concentrations as low as 17.7 microg/L.
authors.affiliation: Kurume Research Laboratory, Chemicals Evaluation and Research Institute, Japan, Kurume-shi, Fukuoka. yokota-hirofumi@kurume.cerij.or.jp
authors.forename: H
authors.initials: H
authors.lastname: Yokota
authors.forename: M
authors.initials: M
authors.lastname: Seki
authors.forename: M
authors.initials: M
authors.lastname: Maeda
authors.forename: Y
authors.initials: Y
authors.lastname: Oshima
authors.forename: H
authors.initials: H
authors.lastname: Tadokoro
authors.forename: T
authors.initials: T
authors.lastname: Honjo
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
mesh_terms: D000818:Animals; D004625:Embryo, Nonmammalian / Q000187:drug effects; D047108:Embryonic Development; D005260:Female; D006066:Gonads / Q000187:drug effects / Q000254:growth & development; D007814:Larva / Q000187:drug effects / Q000254:growth & development; D008297:Male; D009990:Oryzias / Q000502:physiology*; D010636:Phenols / Q000633:toxicity*; D012098:Reproduction / Q000187:drug effects*; D012733:Sex Differentiation / Q000187:drug effects*; D012744:Sex Ratio; D016019:Survival Analysis; D013550:Swimming; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D010636:Phenols; D014874:Water Pollutants, Chemical; C041594:4-nonylphenol