Are BKME Effects on Fish Caused by Chlorinated Compounds?

by B.K. Burnison, P.V. Hodson, J. Parrott, A. Schnell, M. Comba and J. Carey

[Note: "BKME" means bleached kraft mill effluent. This paper was presented before the Division of Environmental Chemistry, American Chemical Society, August 21-26, 1995. It will not appear in the ACS proceedings, but the authors will make the findings of this project available through papers in the professional literature. The authors' summary of this paper, prepared for a news conference at the ACS meeting, has been edited, with the help of the first author, for publication in the Alkaline Paper Advocate.]

Much of the debate about the use and environmental impacts of organic chlorinated compounds has arisen from attempts to regulate the effluents discharged by pulp and paper mills. The chlorinated compounds in pulp mill effluents have been crudely estimated by the AOX (adsorbable organic halide) content. In some countries, the concentration of AOX in the effluent of pulp and paper mills is regulated. The authors believe that this is unwarranted, because many of the effects which have concerned scientists do not correlate with AOX concentration.

They tested for the presence of deleterious chemicals by looking at the levels of certain liver enzymes produced by fish. These enzymes are called mixed function oxygenases (MFOs). The induction of MFOs is a sub-lethal effect and, as such, is considered a "red flag" to tell us that the fish have been exposed to damaging chemicals.

Studies of wild fish populations in Canada have shown that elevated MFO activity and many indicators of reproduc-tive impairment occur in streams below pulp mills. These effects occur even when the pulp mill does not use chlorine as a bleaching agent, for example below sulphite, thermomechanical and unbleached kraft mills. The modernization of bleached kraft mills has virtually eliminated the discharge of chlorinated dioxins and furans and greatly reduced concentrations of chlorinated phenolics in effluents. Secondary (biological) treatment of these cleaned-up effluents prevents some but not all of the effects on fish.

The first author, Dr. Kent Burnison of the Canadian National Water Research Institute in Burlington, Ontario, presented evidence that MFO induction can occur when fish are exposed to process liquid from initial stages in the pulping process (i.e., before bleaching). Black liquor, the residual liquor from the kraft cooking process, strongly induced MFOs. This indicates that chemicals extracted directly from wood may be responsible for the observed effects in fish. (In practice, approximately 97% of black liquor is recycled within the mill, not discharged into lakes and rivers.)

The Canadian research group has isolated groups of related MFO-inducing chemicals from pulp mill effluent. Currently, they are looking at the types of compounds contained in the active fraction to determine which chemicals are responsible. They have found both chlorinated and nonchlorinated compounds. Some of the nonchlorinated compounds have been shown to induce MFOs.

The results so far support the hypothesis that MFO-inducing chemicals in pulp mill effluents may not be chlorinated. Simply reducing the discharge of chlorinated compounds, as represented by AOX, is unlikely to prevent important effluent effects on fish populations.