Effects of phytosterols and estradiol on maturation and reproduction in fathead minnows

Abstract

Phytosterols have been detected in the dissolved portion of secondary treated pulp and paper mill effluent at concentrations of approximately 100 to 300 ug/L. $\beta$-sitosterol, which represents approximately 90% of the phytosterols in effluent, resembles the female hormone 17$\beta$-estradiol. It has been hypothesized that the release of $\beta$-sitosterol from pulp and paper mills may contribute to adverse impacts on fish reproduction. Juvenile fathead minnows (Pimephales promelas) were exposed to either a waterborne mixture of phytosterols (containing mainly $\beta$-sitosterol) or pure estradiol in a partial life-cycle test to determine if phytosterols could alter secondary sex characteristics, gonadosomatic index (GSI), gonadal sex steroid concentrations, or egg production. 17$\beta$-estradiol (0.25 ug/L) caused a delay in the onset of secondary sex characteristics in male fish. Graded, nominal, concentrations of phytosterols (3-100 ug/L) did not cause a significant difference in fathead minnow maturation or egg production. Egg production was highly variable between early and late spawning control fish, indicating that many replicates may be needed for this endpoint to be of use. Once fathead minnows matured sexually in estradiol and phytosterol treatments, they had GSI and gonadal sex steroid concentrations comparable to those of control fish. Although phytosterols are present in pulp and paper mill effluent, the concentrations tested here show no adverse effects on sexual maturation and egg production in fathead minnows. However, the response to 17$\beta$-estradiol shows the potential of this fathead minnow partial life-cycle test to detect estrogenic substances.