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Chlorine Dioxide:
A Single Atom Makes All the Difference


One atom can make all the difference in the world. Change one atom and the neutral smell of water becomes the stench of a poisonous gas. Lose an oxygen atom when chlorophyll decays, and the colors of an autumn fall develop. The same is true for environmental effects: slight changes in a molecule's make-up can signal dramatic environmental benefits.

Take chlorine, for example, which was once used to make paper white. There's a raging debate over its use, but this has created more heat than light. For instance, remove one chlorine atom in the chlorine gas molecule and replace it with two of oxygen to create chlorine dioxide.

"So you would think chlorine dioxide is similar to chlorine since they both have the same word in their names. But the chemistry is fundamentally different. Hydrogen is in both water and hydrogen cyanide, but the latter can be a deadly gas," said Doug Pryke, Executive Director of the Alliance for Environmental Technology (AET).

Chlorine dioxide is today the best bleaching agent bar none in terms of environmental performance and product quality. "In fact, chlorine dioxide is a solution to the problem of persistent, bio-accumulative toxic substances in mill waste water," added Dr. Donald Mackay of the International Joint Commission Virtual Elimination Task Force.

AET is a group of North American chemical manufacturers established to research and promote proven, practical technologies to raise the environmental performance of the pulp and paper industry. AET commissioned an assessment of the ecological effects of chlorine dioxide bleaching. The report, written by a panel of some of the world's foremost scientists in the field, was the first of its kind to follow the US Environmental Protection Agency's Framework for Risk Assessment.

The authors reached a unanimous opinion. "The environmental risks of chlorinated organics, i.e. chlorine containing substances, in the waste water of a modern mill using chlorine dioxide bleaching are insignificant," stated Dr. Keith Solomon, Director of The Centre for Toxicology, who along with Dr. Mackay helped prepare the report.

In short, the public should not have to worry about the risks to human health and to the environment from chlorine dioxide.

These dramatic findings result from the way chlorine dioxide reacts with organic material such as lignin, the tissue that hold a plant's cellular wall together, and which is eliminated during bleaching. Chlorine gas reacts with lignin to create certain compounds that can be potentially harmful. Chlorine dioxide, on the other hand, breaks these compounds apart. As the rate of chlorine dioxide use approaches 100 percent, the formation of these potentially harmful substances falls to zero.

Small changes in molecular structure can generate very large differences in effect. The molecules responsible for the striking blue of the cornflower differs only from the scarlet red of the periwinkle by one hydrogen atom -- an example of the wonders of the natural world.

And in papermaking, the switch from molecular chlorine gas to chlorine dioxide -- a seemingly small change on the molecular level -- results in significant environmental improvement. "It's an elegant solution to a complex problem," said Pryke.