The United States government has ordered the country's coal-burning power plants to reduce mercury pollution by nearly 70 percent over the next 13 years.  The nation is the first in the world to decree reductions of the toxic metal from electric plants, but environmentalists say the new regulation is actually much weaker than the existing clean air law.

The U.S. Environmental Protection Agency (EPA) says three percent of the world's mercury pollution comes from U.S. sources, and one-third of that, or one percent of the world total, is emitted by American coal-fueled power plants.

The agency's top air pollution official, Jeffrey Holmstead, says the new Bush administration rule aims to cut back that one-percent. Electricity utilities have until 2018 to cut mercury emissions 70 percent below 1999 levels.

"There are literally thousands of coal-burning power plants throughout the world,” he said.  “The United States is the first nation to take a leadership role in addressing the problem of mercury from power plants."

Mercury is toxic to babies' nervous systems, and several studies have linked it to heart disease. Most U.S. states urge their residents, especially children and women of childbearing age, to limit consumption of certain fish known to absorb high mercury levels.

The U.S. government intends to reach its mercury reduction goals by creating an emissions market. Companies that lower their mercury pollution to meet interim limits can sell pollution credits to plants that clean up more slowly. These credits allow the slower acting plants not to meet the deadlines as long as enough others do. The concept is called cap and trade. Mr. Holmstead says that making pollution a tradable commodity, combined with penalties for non-compliance, gives power plants strong motivation to make early mercury reductions and invest in pollution control technologies.

"Cap and trade programs are specifically designed so that you don't have everybody trying to meet a certain date,” he said.  “It is not as though the whole industry goes to 2010 and then drops off and then goes on until 2018 and drops off. The whole design of the program is to have the emission reductions start right away and to increase over time in this gradual line."

But environmental groups call the plan a gift to the power industry. The Natural Resources Defense Council says the rule uses the label of pollution trading as cover to allow power plants to spew excessive amounts of mercury for many more years. One of the council's lawyers is Jon Devine.

"Let's be clear. This cap and trade scheme, because power plants can buy pollution credits rather than clean up, will not reduce mercury pollution by 70 percent in 2018 as is often reported," said Mr. Devine.

Opponents also say the new procedure unfairly allows some areas of the United States to suffer higher mercury pollution than others rather than applying equal standards throughout the country. In addition, they argue that it fails to meet guidelines established in existing clean air legislation. Jon Devine says the present law, if enforced, would lead to a 90 percent reduction in power plant mercury emissions by 2008.

"The current law requires sources of hazardous pollutants like mercury to install the maximum achievable controls and to do so within a very short time frame, three years,” he added.  “What the cap and trade scheme does is to give power plants an extended time frame to do much less than what is maximally achievable."

But supporters of the mercury trading plan say it is the cheapest way to reduce the pollutant. The U.S. Environmental Protection Agency argues that keeping the cost of the process down ensures the continued flow of affordable electricity and protects the use of coal, an abundant source of fuel.