Fathead minnow response to broad-range exposure of ß-sitosterol concentrations during life-cycle testing.

The ß-sitosterol concentration in pulp and paper mill effluents is typically greater than that of other phytosterols and has been shown to cause a variety of effects in fish. The authors exposed fathead minnow (Pimephales promelas) to low (22 ± 0.93 µg/L), medium-low (70 ± 2.1 µg/L), medium-high (237 ± 5.5 µg/L), and high (745 ± 16.2 µg/L) concentrations of ß-sitosterol as well as negative (water), positive (ethynyl estradiol, 16 ± 0.58 ng/L), and carrier (0.6 mL/L acetone) controls. Fish were monitored over a full life cycle for population-level endpoints including growth and survival, reproductive endpoints (e.g. fecundity, sex steroids and vitellogenin, gonado-/hepatosomatic indices, and gonad histology). No significant differences were seen in fish growth, mortality, or reproduction with ß-sitosterol exposure, although a trend for lower egg production in ß-sitosterol exposures relative to the water control may be related to the acetone carrier. All ethynyl estradiol-exposed fish were smaller, showed female characteristics, and did not spawn. Sex steroid and vitellogenin were highly variable with no detectable treatment-related differences. Gonadal tissue showed no ß-sitosterol-related differences in reproductive development and spawning capability, although most ethynyl estradiol-exposed males had ovarian tissue and were not spawning-capable. The results indicate that ß-sitosterol exposure had little apparent impact on fathead minnow survival, growth, and reproduction even at concentrations >10 times that of typical effluents, although small sample size and variability precluded fully evaluating treatment responses on sex steroids and vitellogenin.

Responses of fathead minnows (Pimephales promelas) during life-cycle exposures to pulp mill effluents at four long-term receiving water study sites.

We exposed fathead minnows (Pimephales promelas to 7 concentrations of effluents from pulp mills at 4 Long-Term Receiving Water Study (LTRWS) sites. The primary objective of these investigations was to determine the potential for toxicity, particularly on fish reproduction, of the pulp mill effluents using laboratory tests. These tests were performed as LTRWS fish community assessments were being completed, thus results of the laboratory fish reproduction tests could be compared to in-stream fish community measurements. In general, bioindicators measured during the life-cycle tests, including gonadosomatic index (GSI), hepatosomatic index, condition factor, numbers of tubercles on heads of males and females, and gonadal histology did not show consistent patterns or dose response and did not predict effects on egg production. Gonadosomatic indexes and tubercles also did not indicate estrogenic or androgenic responses to the effluents during the life-cycle tests. The most consistently sensitive test endpoint showing a dose response was the 25% inhibition concentration (IC25) for egg production. Based on this endpoint all 4 effluents had effects on fish reproduction from 8% by volume to 100% effluent. However, in-stream effects on fish reproduction would not be expected based on these 4 life-cycle tests for any of the LTRWS stream sites. The mean effluent concentration in Codorus Creek, Pennsylvania, USA was approximately 32%, and the IC25 for the life-cycle test was 100% effluent, providing a margin of safety of approximately 3 times. The margins of safety at the other sites are much greater: 34 times for Leaf River, Mississippi, USA (IC25 = 69%, 2% mean receiving water concentration), 36 times for the McKenzie River, Oregon, USA (IC25 = 18%, 0.5% mean receiving water concentration), and 40 times for the Willamette River, Oregon, USA (IC25 = 8%, 0.20% mean receiving water concentration). Effects on fish numbers, diversity, and community structure due to the effluent were also not found during the LTRWS, which is consistent with these laboratory results. These findings indicate that in this case, when laboratory results combined with in-stream effluent concentrations suggest in-stream effects on fish population are not expected, the laboratory results are consistent with the in-stream observations. However, inferences about situations where laboratory results predict in-stream effects cannot be made from these data.