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

Adult fathead minnows (Pimophales promelas) were exposed to waterborne conc entrations 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 conduc ted during July and August, near the beginning of the breeding season, and a second experiment conducted during September and October, at the end of t he breeding season, during which the adults were maintained continuously in breeding condition, inverted U-type dose response relationships were obser ved for egg production and fur concentrations of vitellogenia (Vtg) and 17 beta-estradiol (E-2) in blood plasma. Concentrations of plasma Vtg were sig nificantly different between males and females, with plasma concentrations in females ranging from 20 to 110 mu g Vtg/ml. Both experiments had no stat istically significant, dose-dependent effect of NP on plasma Vtg in males b ut significant effects of NP on Vtg concentrations in females. In the first experiment, Vtg concentration generally increased with NP concentration, w hereas the second experiment showed a negative correlation. Plasma E-2 conc entrations in both males and females were significantly affected by TcTP. T he concentration of total estrogen equivalents in the plasma increased 900% because of exposure to NP. Most of this increase resulted from increased p lasma E-2 concentrations, with only a 4% increase resulting from the estrog en 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 fr om changes in the endogenous concentrations of E-2 through an indirect acti vation mechanism of action.