Technical Bulletin No. 0788: Effects of the Phytosterol Stigmastanol on Early Life-Stages and Life-Cycles of Fathead Minnows and Ceriodaphnia dubia

Previous NCASI laboratory studies found that effluent from kraft mills, bleached kraft mills, and an OCC recycle mill reduce egg production during fathead minnow life-cycle tests at concentrations from 18% to 100% v/v of effluent. Although the concentrations causing effects were much greater than most in-stream water concentrations, determination of the source of these effects may be useful because, as processes are modernized, identified sources may be considered for reduction. Two of the goals of the aquatic biology studies; of which the work reported herein is a component; are to (1) determine if specific compounds in the effluents alter fish reproduction, and (2) determine the sources of compounds that affect reproduction. Comparisons between concentrations of components measured in pulp and paper mill effluents and reproduction endpoints from fathead minnow lifecycle tests found a very limited number of strong correlations. The strongest correlation was with stigmastanol, a naturally occurring phytosterol. Therefore, this compound was tested to determine if it may have been responsible for effects on reproduction during previous life-cycle bioassays. Fathead minnow (Pimephales promelas) 7-d, 28-d, 56-d, and life-cycle bioassays, as well as several biomarker responses, and a Ceriodaphnia dubia 7-d bioassay were completed using stigmastanol, dissolved in an acetone carrier. C. dubia 7-d survival and reproduction were not reduced from the controls in any of the stigmastanol concentrations (NOEC=99.2 mcg/L), and the IC25s were >99.2 mcg/L of stigmastanol, which was the highest concentration tested. Survival and growth of fathead minnows during one 7-d bioassay were reduced at the highest stigmastanol concentration tested (99.