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

<jats:title>Abstract</jats:title><jats:p>A fish full life‐cycle (FFLC) study was conducted for 17α‐ethinylestradiol (EE<jats:sub>2</jats:sub>) using the fathead minnow, <jats:italic>Pimephales promelas.</jats:italic> Newly fertilized embryos (&lt;24 h old) were exposed to five concentrations of EE<jats:sub>2</jats:sub> (0.2, 1.0, 4.0, 16, and 64 ng/L nominal) in continuous flow‐through conditions for 305 d at 25 ± 1°C. Exposure concentrations were verified by <jats:sup>14</jats:sup>C‐EE<jats:sub>2</jats:sub> radiochemistry, supported by radioimmunoassay, and mean measured values were ≥70% of nominal. For the F<jats:sub>0</jats:sub> adult phase until 301 d posthatch, the no‐observed‐effect concentrations (NOECs) for growth, survival, and reproduction (as egg production) were all ≥ 1.0 ng/L. The NOEC values for F<jats:sub>1</jats:sub> embryo hatching success and larval survival (at 28 d posthatch) were both ≥ 1.0 ng/L. While statistically detectable changes in F<jats:sub>1</jats:sub> growth were evident at 0.2 ng/L, these were not considered to be biologically significant when compared with historical control data. Male fish exposed to EE<jats:sub>2</jats:sub> at 4.0 ng/L failed to develop normal secondary sexual characteristics; on the other hand, assumed females exposed to this level of EE<jats:sub>2</jats:sub> were able to breed when paired with males that had not been exposed to EE<jats:sub>2</jats:sub>. Histology of F<jats:sub>0</jats:sub> control, 0.2‐, and 1‐ng/L exposed fish at 56 d posthatch indicated an approximate female‐to‐male (F:M) sex ratio of 50:50 (with no ovatestes observed in the control), while fish exposed to EE<jats:sub>2</jats:sub> 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 testicular tissue was observed in any fish exposed to EE<jats:sub>2</jats:sub> at 4.0 ng/L. At the same time point, plasma vitellogenin levels were significantly higher in fish exposed to EE<jats:sub>2</jats:sub> at 16 ng/L. A lack of sexual differentiation occurred in males at concentrations ≥4.0 ng/L. Taking into account these data, the overall no‐observed‐adverse‐effect concentration was considered to be 1.0 ng/L.</jats:p>