Further insights into the potential of pulp and paper mill effluents to affect fish reproduction

As part of a continuing survey, effluents from five mills in Canada were tested in the laboratory for their potential to affect fish reproduction. The study included effluents from two thermomechanical pulp (TMP) mills, two kraft pulp mills, and one mill that used both chemical and mechanical pulping. The laboratory test used adult fathead minnows and involved a 21-day exposure to each effluent. All the effluents were tested at 2 and 20% concentration. The effluent from 1 of the kraft mills was also tested at 40% concentration. The endpoints of the test included, egg production, gonad size, sex steroids, secondary sexual characteristics, and vitellogenin concentration in males, considered to be an indicator of estrogenicity. The results of this study were similar to the results of our previous survey. None of the effluents produced noteworthy changes at 2% concentration. At 20% concentration, only the effluent from the multiprocess mill produced a significant reduction in eggs, which was considered to be the most important indicator of reproductive performance. Some effluents did produce an increase and/or a decrease in a variety of endpoints other than egg production, but the most consistent response was an induction of vitellogenin in males exposed to three of the five effluents tested. In summary, these results indicate that most mill effluents up to 20 or 40% concentration do not affect the overall reproductive capacity of minnows in the laboratory. However, the mill effluents do seem to contain substances that cause vitellogenin induction.