Inhibition of barnacle settlement by the environmental oestrogen 4-nonylphenol and the natural oestrogen 17β oestradiol

The present study examines the effect of a known environmental oestrogen, 4-nonylphenol, on the settlement of the cypris larva of the barnacle, Balanus amphitrite. Cypris larvae were exposed to 4-nonylphenol in a nominal concentration range of 0.01–10.0 μg l−1. Definitive concentrations of 4-nonylphenol in the test solutions were determined by GC/MS. Cyprid settlement was reduced significantly within this concentration range, following incubation at both 25°C and 28°C for 24–48 h. A naturally occurring oestrogen, 17β oestradiol, was used as a positive control, in the concentration range 0.01–10.0 μg l−1. Larval settlement was inhibited by 17β oestradiol, but the trend was the opposite to that seen with 4-nonylphenol. No evidence of endocrine disruption was demonstrated, but significant inhibition of larval settlement by both 4-nonylphenol and 17β oestradiol indicated that the compounds may have toxic effects at environmentally realistic and naturally occurring concentrations. The potential for endocrine disruption being more significant at different developmental stages in barnacles is discussed.