Coal-fired power plants are the largest single source of mercury pollution in the country. They are also unregulated when it comes to this toxin, making the Environmental Protection Agency’s announcement last week that it will begin to limit mercury emissions much-needed and overdue. Supporting these restrictions beyond the end of the Clinton administration will help show whether President-elect Bush is serious about improving the environment.

After Congress determined in 1998 that mercury was the most dangerous of all air pollutants, the EPA was directed to determine whether reductions were necessary. The agency will develop regulations over the next three years, with final work scheduled for 2004. The time is necessary to hear from all sides affected by the decision and allow the owners of power plants – by far the largest producer of airborne mercury – and incinerators time to prepare for the changes.

The United States is a small contributor to the global mercury problem, making up only about 3 percent of total man-made and naturally occurring mercury emissions. That percentage should drop even further over the next decade now that the EPA has addressed emissions at municipal, medical and hazardous waste incinerators and gotten it out of paints and pesticides. Industry, too, has contributed through voluntary reductions, finding alternatives in, for instance, batteries, thermometers and other household goods, and working with state governments to establish local regulation. The federal action on power plants brings reductions to the last major emissions contributor.

There is good reason to try to reduce mercury emissions whenever possible. At high doses, mercury can cause tremors, convulsions, kidney failure, deafness, blindness, even death. Exposure is especially serious to developing fetuses and, therefore, to women of childbearing ages. Mercury in the environment is blamed for affecting wildlife including, in Maine, bald eagles.

Making a measurable difference in mercury reduction when most of the emissions happen somewhere else, however, isn’t easy. Just as mercury is diffuse in the environment, so are the sources of emissions, both here and abroad. EPA can’t do much to stop emissions in other countries, but it can do this: Tack onto its new power plant regulations rules for instructing the federal government to buy (there’s a glut of mercury on the world market, prices are low) mercury from industries getting out of the mercury-spewing business. Maine tried to get the Department of Defense to help out with the 260,000 pounds HoltraChem had for sale, but federal statute prevented it. It went on the world market and will someday revisit Maine in microscopic form as it descends from the clouds. On this issue, in fact, there’s no reason to wait for 2004; EPA should suggest it now and ask Congress to fund the program.

As pressure has increased on the makers of products containing mercury, they have responded with either significant reductions or entirely mercury-free alternatives. The options are not that simple for the owners of power plants, but they, too, can make cuts that will reduce the amount of man-made mercury in the air. The EPA properly gave notice and a generous deadline to do it.