Effects of 4-nonylphenol on fecundity and biomarkers of estrogenicity in fathead minnows (Pimephales promelas)

Adult fathead minnows (Pimophales promelas) were exposed to waterborne concentrations of 4-nonylphenol (NP) ranging from 0.05 to 3.4 mu g NP/L for 42 d. Results were similar, but slightly different, for two experiments conducted during July and August, near the beginning of the breeding season, and a second experiment conducted during September and October, at the end of the breeding season, during which the adults were maintained continuously in breeding condition, inverted U-type dose response relationships were observed for egg production and fur concentrations of vitellogenia (Vtg) and 17 beta-estradiol (E-2) in blood plasma. Concentrations of plasma Vtg were significantly different between males and females, with plasma concentrations in females ranging from 20 to 110 mu g Vtg/ml. Both experiments had no statistically significant, dose-dependent effect of NP on plasma Vtg in males but significant effects of NP on Vtg concentrations in females. In the first experiment, Vtg concentration generally increased with NP concentration, whereas the second experiment showed a negative correlation. Plasma E-2 concentrations in both males and females were significantly affected by TcTP. The concentration of total estrogen equivalents in the plasma increased 900% because of exposure to NP. Most of this increase resulted from increased plasma E-2 concentrations, with only a 4% increase resulting from the estrogen agonist activity of NP. The effects of NP on adult fathead minnows seem not to result from a direct-acting estrogen agonist mechanism but rather from changes in the endogenous concentrations of E-2 through an indirect activation mechanism of action.