INTRODUCTION

Pulp is produced by several methods. These production techniques yield different products and by-products. Although it is possible to generally classify mills by their process technology, this results in an oversimplification of the nature and concentrations of the products and byproducts of the mills. The degree to which chemicals released from pulp and paper production will potentially have an impact on the receiving water is dependent on several factors. These are: the wood species used, the degree of spill control and pulping liquor recovery, the bleaching process (if any) and the degree to which mill effluent is treated before being released. Effluent treatment technology has changed rapidly. Potential environmental impacts may differ significantly over time and from one receiving environment to another as well. Thus, it is important to realize that effluents from pulp mills are not necessarily comparable from one mill to the other or over time at any particular location. In the pulp and paper industry, as a result of the research conducted during the Swedish Environmental Cellulose I project, the focus of concerns has been directed towards bleaching with chlorine and the possible effects of the products formed during that process. This is an area of general concern among the public, governments and industry and has resulted, inter alia, in suggestions for restrictions (IJC, 1991; 1994).

This review focuses on the effects of pulp mill effluents in the aquatic ecosystem (including possible effects on wildlife via bioaccumulation through the food chain). The assessment concentrates primarily on the nature, sources, fate and effects of organochlorine chemicals which may be produced during pulp bleaching using chlorine dioxide (ClO₂) and the benefits which result from replacing elemental chlorine (Cl₂) with chlorine dioxide. This risk assessment followed the general guidance set forth in the "Framework for Ecological Risk Assessment" (U.S. EPA, 1992).

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