Bisphenol A induces superfeminization in the ramshorn snail Marisa cornuarietis(Gastropoda: Prosobranchia) at environmentally relevant concentrations

Abstract

Previous investigations have shown that bisphenol A (BPA) induces a superfeminization syndrome in the freshwater snail Marisa cornuarietis at concentrations as low as 1 microg/L. Superfemales are characterized by the formation of additional female organs, enlarged accessory sex glands, gross malformations of the pallial oviduct, and a stimulation of egg and clutch production, resulting in increased female mortality. However, these studies were challenged on the basis of incomplete experimentation. Therefore, the objective of the current approach was to bridge several gaps in knowledge by conducting additional experiments. In an initial series of experiments, study results from the reproductive phase of the snails were evaluated in the sub-micrograms per liter range. Before and after the spawning season, superfemale responses were observed [NOEC (no observed effect concentration) 7.9 ng/L, EC10 (effective concentration at 10%) 13.9 ng/L], which were absent during the spawning season. A further experiment investigated the temperature dependence of BPA responses by exposing snails at two temperatures in parallel. The adverse effect of BPA was at least partially masked at 27 degrees C (EC10 998 ng/L) when compared with 20 degrees C (EC10 14.8 ng/L). In M. cornuarietis, BPA acts as an estrogen receptor (ER) agonist, because effects were completely antagonized by a co-exposure to tamoxifen and Faslodex. Antiandrogenic effects of BPA, such as a significant decrease in penis length at 20 degrees C, were also observed. Competitive receptor displacement experiments indicate the presence of androgen- and estrogen-specific binding sites. The affinity for BPA of the estrogen binding sites in M. cornuarietis is higher than that of the ER in aquatic vertebrates. The results emphasize that prosobranchs are affected by BPA at lower concentrations than are other wildlife groups, and the findings also highlight the importance of exposure conditions.

Figure 1

Marisa cornuarietis, exposure series I. Cumulative egg production in groups exposed to BPA and EE₂ (positive control), normalized for number of females, for the entire experiment (A) and separated for the phases before (B), during (C), and after the main spawning season (D). All concentrations are provided on a nominal basis. Significant differences from solvent control (SC): *p < 0.05; **p < 0.01, ANCOVA with Student-Newman-Keuls as post-hoc tests).

Figure 2

Marisa cornuarietis exposure series II at 20°C (A,C,E) and 27°C (B,D,F ). (A,B) Cumulative egg production in groups exposed to BPA alone or in combination with either faslodex (ICI) or tamoxifen (Tam), normalized for number of females. Egg production per female (C,D) and mortality (E, F) during the entire experiment. Concentrations are provided on a nominal basis; biological parameters are given as mean values (n = 2) with SD. Asterisks indicate significant differences from SC: *p < 0.05, **p < 0.01, #p < 0.001; ANCOVA with Student-Newman-Keuls as post-hoc tests in A and B; ANOVA with Student-Newman-Keuls as post-hoc tests in C and D; χ² test in E and F).

Figure 3

Marisa cornuarietis. Competitive displacement of specific [3H]-E₂ (A) and [3H]-T binding (B). Mean curves (n = 3) with SE demonstrate displacment activities of T, E₂, BPA, and Tam compared with [3H]-E₂ and displacement activities of E₂, T, BPA, and MT compared with [³H]-T.