Environmental Protection Agency Administrator Carol M. Browner today announced a plan aimed at sharply reducing levels of mercury, dioxin and several other of the most toxic industrial chemicals discharged into the Great Lakes.

The plan would prohibit dumping the chemicals into so-called "mixing zones" in Illinois, New York, Ohio and Pennsylvania. It also is designed to reduce the flow of mercury from direct discharges through outfall pipes by as much as 90 percent, Browner said. Mixing zones--areas where the listed chemicals can mix with water and dilute--already have been eliminated by the governors of Indiana, Michigan, Minnesota and Wisconsin.

"The risks posed to human health and to the Great Lakes themselves by these toxic pollutants are simply too high to ignore," Browner said in a speech to the International Joint Commission in Milwaukee, where she made the announcement. The United States and Canada formed the commission in 1909 to help govern shared waterways.

The wastes covered by the proposal, known as "bioaccumulative chemicals of concern," include mercury, polychlorinated biphenyls (PCBs), dioxin, chlordane, DDT and mirex, Browner said. Some of the biggest polluters in the Great Lakes Basin, according to environmentalists, are the iron and steel plants that ring the lakes.

If ratified after a 60-day period of public comments, the new EPA regulations would prohibit new discharges of the listed chemicals into mixing zones and phase out the use of existing mixing zones over the next 10 years.

Browner said the notion that a "toxic plume" of industrial waste reaches safe levels by the time it leaves a mixing zone is unsound.

"Bioaccumulating toxic chemicals are not known for their ability to become diluted. By allowing poisons to gather first in mixing zones, we guarantee that over time they will spread and accumulate throughout the delicate environment of the Great Lakes," she said.

Calling the Great Lakes a "shared national treasure," Browner said she will work with state and local governments, environmental groups and industries to review mixing zones elsewhere and determine if they should be phased out in all of the nation's waterways.

In 1995, the EPA and the Great Lakes states agreed to water-quality standards that covered 29 pollutants, including bioaccumulative chemicals, and called for an end to mixing zones. However, the iron and steel industries challenged the plan in federal court. In 1997, the U.S. Court of Appeals in the District upheld most of the provisions but struck down the mixing zone prohibition and sent it back to the EPA for review because of the potential cost to industry.