Changes in growth, secondary sex characteristics, and reproduction of fathead minnows exposed for a life cycle to bleached sulfite mill effluent

To assess the potential effects of exposure to bleached sulfite mill effluent, long-term fathead minnow (Pimephales promelas) exposures were carried out on-site at the pulp mill secondary treatment lagoons. Exposure concentrations included 0, 1, 3, 10, 30, 50, or 100% final effluent, with the synthetic estrogen ethinylestradiol (10 ng/L) as a positive control compound. Fertilized minnow eggs were hatched in effluent and monitored through 140 d posthatch. The effluent produced a significant increase in the growth (length, weight, condition factor) of female fish (but not male fish). Exposure to high effluent concentrations resulted in a majority of fish with female secondary sex characteristics. Male fish with female characteristics and female fish with male sex characteristics were present at effluent concentrations of 30%, but not in fish exposed to control water from the Saint John River. Effluent exposures (greater than or equal to30%) also produced a reduction in the number of fish with testes, and most fish had ovaries when examined internally. A sensitive and meaningful endpoint was a decrease in reproduction. Fish exposed to 1-3% effluent produced a similar number of eggs to control fish; however, exposure to 10% effluent reduced egg production by over 80%. Fish exposed for an entire life cycle to greater than or equal to30% effluent failed to produce eggs. The research demonstrates the feasibility and potential usefulness of on-site flow-through fish life-cycle exposures for the assessment of pulp mill final effluents.