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"A Review and Assessment of the Ecological Risks Associated with the Use of Chlorine Dioxide for the Bleaching of Pulp"

Summary Report


There is an on-going international debate among governments, industry and the public over the industrial use of chlorine. One focus of concern is the possible environmental effects of chlorinated organics, chemical substances found in mill waste water which are formed by using chlorine in papermaking.

A number of policy responses have been put forward. These responses range from a regulatory ban on all chlorine and chlorine-containing compounds, to voluntary efforts to minimize the generation of a select group of toxic substances, including dioxin.

The International joint Commission (IJC), the Canadian-American bilateral organization established to monitor the Great Lakes Water Quality Agreement, has recommended sunsetting (phasing out) the use of chlorine and chlorine-containing compounds as industrial feedstocks (IJC, February 1994). In addition, President Clinton submitted to the US Congress on Feb. 1, 1994 a proposal that included a provision to develop a national strategy to control the use of chlorine and chlorinated compounds.

In anticipation of these events, the Alliance for Environmental Technology requested a panel of five eminent scientists to prepare an opinion on the effects of chlorine dioxide -- an alternative to chlorine gas as a pulp bleaching agent -- on the nature, quantity, environmental exposures and environmental impact of chlorinated organic compounds produced in papermaking.

Results of the Risk Assessment

The panel of scientists reached a unanimous opinion. Their report clearly demonstrates that using chlorine dioxide in papermaking provides considerable environmental benefits.

The panel believes that the weight-of-evidence from laboratory studies, risk analyses and field observations demonstrates that chlorine dioxide bleaching process provides the following benefits:

  • Eighty percent reduction in the quantity, and 90 percent reduction in the degree of chlorination, of the chlorinated organics detected in mill waste water;

  • Decrease in the persistence of these compounds, and their potential for bio-accumulation and food chain transfer;

  • Reduction in the potential for negative ecological effects; and

  • In particular, virtual elimination of the formation of dioxin.

Based on the available data, the panel concludes that chlorinated organics from mills bleaching with chlorine dioxide, employing secondary treatment and with receiving water dilutions typical of most mills in North America, present an insignificant risk to the environment.

These results follow from the fundamental chemical difference between chlorine dioxide and chlorine, and the way in which these two chemicals react with organic compounds, such as lignin (the cellular adhesive in wood tissue).

In the chlorine-based bleaching process, a significant portion of the chlorine combines directly with lignin which has "aromatic" components. Aromatic compounds have atoms arranged in rings, and they may have other atoms, such as chlorine, attached to these rings. Within the group of chlorinated aromatics are the infamous dioxins.

Chlorine dioxide's behavior as a bleaching agent is completely different. Instead of combining with the aromatic rings, chlorine dioxide breaks these rings apart. Also, the generation of chlorinated organics falls dramatically as use of chlorine dioxide increases.


The study followed the general guidelines of the US EPA's "Framework for Ecological Risk Assessment" published in 1992.

A conceptual model was built to describe the chemicals anticipated in mill waste water, as well as the environments into which the chemicals would go. Exposure of aquatic organisms to the chemicals present in the waste water was characterized, as were possible adverse biological effects that could occur from exposure. Actual data from mills using chlorine dioxide were then used to estimate the likelihood of ecological effects resulting from realistic exposures to biologically treated waste water.

To complete the risk assessment, the panel reviewed nearly 300 scientific studies and other works.

Science Panel Members

  1. Dr. Keith Solomon, Centre for Toxicology, University of Guelph, Guelph, Ontario (panel chairman)

  2. Dr. Harold Bergman, Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming

  3. Dr. Robert Huggett, Department of Environmental Sciences, Virginia Institute of Marine Sciences, The College of William and Mary, Glouchester Point, Virginia

  4. Dr. Donald Mackay, Institute for Environmental Studies, University of Toronto, Toronto, Ontario, and member of the IJC Virtual Elimination Task Force

  5. Dr. Bruce McKague, CanSyn Chem. Corp., Toronto, Ontario

For a copy of the entire 75-page report, call AET at (800) 999-PULP.