Exposures to Estradiol, Ethinylestradiol and Octylphenol Affect Survival and Growth of Rana pipiens and Rana sylvatica Tadpoles

Abstract

Endocrine disrupting compounds (EDCs) are often detected in the aquatic environment and can negatively affect the health of wildlife populations. However, little is known about the sensitivity of native amphibians to EDCs. Wood frogs (Rana sylvatica) and Northern leopard frogs (Rana pipiens) were exposed to three estrogenic EDCs: estradiol (E₂), ethinylestradiol (EE₂), and 4-tert-octylphenol (OP). In addition, R. pipiens were exposed during two developmental stages (Gosner stages 26 and 36) to examine life-stage differences in sensitivity. Tadpoles were exposed for 2 wk to 8 nominal concentrations (0.25 μM–10 μM) of each compound. Individual mortality was recorded during the exposure period, while body weight was measured at the end of 2 wk. LC₅₀ values were calculated, and differences in body weight between vehicle control and exposed groups were assessed. Rank order toxicity of the compounds for both R. pipiens stages and both species was OP > EE₂ > E₂. Gosner stage 26 tadpoles were more sensitive (LC₅₀: E₂ [5.57 μM], EE₂ [3.01 μM], OP [1.36 μM]) to all three compounds when compared to stage 36 tadpoles (LC₅₀: E₂ [>10 μM], EE₂ [4.17 μM], OP [2.80 μM]). Interspecies comparisons revealed R. sylvatica tadpoles (LC₅₀: E₂ [2.50 μM], EE₂ [1.89 μM], OP [0.74 μM]) as being more sensitive to the three compounds than R. pipiens (LC₅₀: E₂ [4.56 μM], EE₂ [2.75 μM], OP [1.42 μM]). Xenoestrogen exposure also affected tadpole body weight which may have long-term adverse effects on the rate of metamorphosis. These results provide toxicological data needed for assessing sublethal effects of estrogenic compounds on amphibian development and suggest that environmental levels of OP may pose a serious risk to the health of amphibian populations.

The authors thank Bruce Pauli (National Wildlife Research Centre, Environment Canada) for comments on the article. The authors also thank Bill Fletcher for his assistance with animal care. This work was supported by a Natural Science and Engineering Research Council (NSERC) post-graduate scholarship to N. S. Hogan, NSERC grants to D. R. S. Lean and V. L. Trudeau, and a Canadian Network of Toxicology Centres (CNTC) grant to V. L. Trudeau.

Notes

^a Number of replicates (dishes).

^b Number of individual tadpoles measured.

^c Nominal concentration (μM).

^d Significant difference from control (p < .05; Tukey post hoc).

^a Number of replicates (dishes).

^b Number of individual tadpoles measured.

^c Nominal concentration (μM).

^d Significant difference from control (p < .05; Tukey post hoc).

Note. Initial number of tadpoles/treatment = 360. Significant differences in LC₅₀ values between stages are indicated by a different letter superscript (a,b), while differences between compounds within each stage are indicated by a different number superscript (1, 2, 3).

Note. Initial number of tadpoles/treatment = 270. Significant differences in LC₅₀ values between species are indicated by a different letter superscript (a,b), while differences between compounds within each species are indicated by a different number superscript (1, 2, 3).