Effects of the synthetic estrogen 17 alpha-ethinylestradiol on the life-cycle of the fathead minnow (Pimephales promelas)

A fish full life-cycle (FFLC) study was conducted for 17 alpha -ethinylestr adiol (EE2) using the fathead minnow, Pimephales promelas. Newly fertilized embryos (< 24 h old) were exposed to five concentrations of EE2 (0.2, 1.0, 4.0, 16, and 64 ng/L nominal) in continuous flow-through conditions for 30 5 d at 25 :+/- 1 degreesC. Exposure concentrations were verified by C-14-EE 2 radiochemistry, supported by radioimmunoassay, and mean measured values w ere greater than or equal to 70% of nominal. For the F-0 adult phase until 301 d posthatch, the no-observed-effect concentrations (NOECs) for growth, survival, and reproduction (as egg production) were all greater than or equ al to1.0 ng/L. The NOEC values for F-1 embryo hatching success and larval s urvival (at 28 d posthatch) were both greater than or equal to 1.0 ng/L. Wh ile statistically detectable changes in F-1 growth were evident at 0.2 ng/L , these were not considered to be biologically significant when compared wi th historical control data. Male fish exposed to EE2 at 4.0 ng/L failed to develop normal secondary sexual characteristics; on the other hand, assumed females exposed to this level of EE2 were able to breed when paired with m ales that had not been exposed to EE2. Histology of F-0 control, 0.2-, and 1-ng/L exposed fish at 56 d posthatch indicated an approximate female-to-ma le (F:M) sex ratio of 50:50 (with no ovatestes observed in the control), wh ile fish exposed to EE, at 4.0 ng/L for 56 d posthatch had a F: M sex ratio of 84:5 (with ovatestes in 11 % of fish). After 172 d posthatch, no testic ular tissue was observed in any fish exposed to EE2 at 4.0 ng/L. At the sam e time point, plasma vitellogenin levels were significantly higher in fish exposed to EE2 at 16 ng/ L. A lack of sexual differentiation occurred in ma les at concentrations greater than or equal to4.0 ng/L. Taking into account these data, the overall noobserved-adverse-effect concentration was consid ered to be 1.0 ng/L.