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A Decade of Research on the Environmental Impacts of Pulp and Paper Mill Effluents in Canada (1992-2002)

4.1 Development and Application of Bioassays - Summary

The development and application of bioassays for pulp mill effluents (PMEs) have evolved over the past decade with the evolution of the research questions. Figure 3 shows the evolution of the research questions, and the resulting evolution of laboratory bioassays. As the issues of acute lethal toxicity of final PMEs were resolved, the focus moved from short-term acute assays to sublethal tests.

Timeline and evolution of research questions for aquatic bioassays to assess the impacts of pulp and paper effleunts in Canada.

Laboratory tests have been used to answer many of the regulatory and research questions that have arisen related to the effects of pulp and paper mill effluents on aquatic biota. Acute, short-term, laboratory tests have been used to assess final effluents and to track changes in effluent quality over time. Short exposures of fish and invertebrates form part of Federal and Provincial effluent discharge regulations for pulp and paper mills and other industries. Short-term laboratory tests have clearly shown the improvement in final effluent quality following secondary treatment of effluent.

In an effort to predict and investigate impacts on wild fish, laboratory bioassays have been developed to examine MFO induction and steroid depression. Exposures of fish in the laboratory have been used to identify pulp and paper mill-related chemicals that induce MFO and suppress steroids. Short-term laboratory exposures of fish have been used to assess responses of fish to pulp and paper mill effluents, to specific components of pulp and paper mill processes (wood extractives, black liquor) and to discriminate between historical and present day discharges.

These short-term bioassays have enabled specific responses, such as MFO induction or steroid depression, to be linked to mill process streams or waste products. Assessment of MFO induction and steroid reduction caused by pulp and paper mill effluent has enabled comparison of types of mill processes, wood furnish, and effluent treatment. It appears that MFO induction and steroid depression are found in fish exposed to effluent from a variety of mills types, with and without chlorine bleaching, in hardwood and softwood pulping facilities, and before and after effluent treatment.

New genomic techniques have contributed to the ability of laboratory bioassays to detect changes associated with exposure to pulp and paper mill effluents. The development of chromosomal markers to determine the genetic sex of some fish species has led to some novel findings: after 1-month exposure to high concentrations of bleached kraft mill effluent, some male fish had ovaries. Advanced techniques have shown that pulp and paper mill effluent decreases sex steroids in exposed fish, but the gene expression pattern is different than fish exposed to estradiol. These genetic technologies may lead to the development of shorter bioassays that are linked to reproductive effects.

Bioassa ys have been used extensively over the last decade to examine the effects of pulp mill effluents on fish. Longer-term, lifecycle laboratory tests and mesocosm exposures have been used to assess the effects of chronic exposure: growth enhancement of invertebrates and fish, liver enlargement, and decreases in gonad size and fecundity in several fish species. Short-term laboratory tests have assessed individual mill waste streams and have provided information to isolate and treat selected pulp and paper mill wastewaters. Short-term tests have also been used to drive causal investigations in the isolation and identifcation of bioactive compounds.

The most sensitive endpoint in these lifecycle and long-term fish exposures is decreased reproduction. This endpoint is biologically meaningful, but determining thresholds for effects requires lengthy and expensive tests. As the laboratory tests move forward into the next decade, attention will focus on the reproductive endpoints, and the possibility of shortening the fish bioassays while still maintaining sensitivity and biological relevance.

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