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 > or = 30%, but not in fish exposed to control water from the Saint John River. Effluent exposures (> or = 30%) 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 > or = 30% 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.

Yellow perch captured downstream of a bleached sulfite mill had reduced gonad size and fecundity, and circulating steroid levels declined in goldfish exposed to final effluent for 21 d. To assess bleached sulfite mill (BSM) effluent, long-term fathead minnow (Pimephales promelas) growth and reproduction tests were carried out in a flow-through bioassay trailer at the mill secondary treatment lagoons. Fertilized P. promelas eggs were hatched in effluent (0, 1, 3.2, 10, 32, 50, and 100% final effluent with 10 ng/L ethinylestradiol as a positive control compound) and monitored through to 30, 60, and 125 d posthatch. The effluent caused a significant increase in the growth of fish; this effect was evident within 30 d. Fish had changes in secondary sex characteristics at maturity: Male fish had ovipositors in effluent concentrations as low as 3.2%. Higher effluent concentrations (32-100%) resulted in a majority of fish that looked externally like females. Changes in external sex characteristics were the most sensitive endocrine disruption-specific endpoints and required four months of exposure. Exposure to low BSM effluent concentrations (3.2%) resulted in female fish that had male sex characteristics (tubercles and dorsal fin dots). This masculinization of female fish was statistically significant at 10% effluent and was not seen in control fish. Concentrations of final effluent in the Saint John River (Canada) range from less than 1% to 15%, depending on the season and river flow. The research assesses some of the changes seen in fathead minnows exposed to this complex effluent, and demonstrates a threshold of <10% BSM effluent for the most sensitive effects.