Inside 55 million domestic vehicles on the road today sits a small pellet of mercury that functions as a switch to turn your trunk and hood convenience lights on or off and to make your antilock braking systems work. When these switches are not removed before scrapped cars are recycled, the mercury exits from smelter smokestacks and ends up in our lakes and rivers.

The human nervous system is highly sensitive to even small amounts of mercury, and trace amounts can disrupt brain development in fetuses and children. Scientists at New York's Mount Sinai Center for Children's Health and the Environment have estimated that mercury exposure causes reductions in intelligence for between 300,000 and 600,000 American children each year, and also causes disruptions in behavior. Most of these effects will last a lifetime.

Over the past 30 years, domestic automakers have installed more than 200 million mercury switches — containing nearly 250 tons of mercury — in vehicles. When these switches are not removed prior to recycling, the mercury is released to the environment during the steel melting process, threatening public health. Auto switches from pre-2003 automobiles currently represent the largest manufacturing source of mercury air emissions, surpassed only by two combustion sources: coal-fired power plants and industrial boilers.

Once the problem of mercury switches in automobiles was identified, there seemed a simple solution. Give value to the switch so that it would be in the interest of every vehicle dismantler to remove it and get cash, just as they do for headlights, dashboards and every other used vehicle part with value.

Over a decade ago, domestic automakers pledged to phase out mercury switches in new cars and trucks. This phaseout was not completed until model year 2002 after years of advocacy by Environmental Defense and Ecology Center and legislative action in the state of Maine.

In 2001 Environmental Defense and Ecology Center wrote two reports to bring attention to the issue, and formed a partnership with all the trade associations representing companies that handle junked vehicles — the vehicle recyclers, scrap recyclers, steel recyclers and steel manufacturers. This group, called the Partnership for Mercury-Free Vehicles, developed model state legislation requiring the removal of all mercury switches from junked cars and mandating automaker responsibility for buying the switches from the dismantlers.

Now, five years later, 10 states — Maine, New Jersey, Arkansas, Rhode Island, North Carolina, South Carolina, Utah, Illinois, Iowa and Massachusetts — have passed laws based on the model, with the value on the switches ranging from $2 to $5 per switch. About the same number of states have created voluntary programs where, for the most part, the switches have no value except for free recycling.

We have now reached another major watershed in the effort to eliminate mercury pollution. After months of negotiation facilitated by the Environmental Protection Agency, all parties — environmentalists, automakers, recyclers and steel manufacturers — have announced a landmark agreement creating a new, industry-funded national program for recovering mercury switches from vehicles before they are dismantled and melted for recycling. This program will greatly reduce this major source of mercury pollution and will complement the state laws already in place.

Under the new national program, auto dismantlers and others who remove switches will submit them to the program for proper management. Automakers will take responsibility for collection, transportation and recycling of the switches. Steelmakers and those who produce steel scrap will promote participation in the program and also ensure mercury switches are removed. Additionally, automakers and steelmakers will create a fund to provide financial incentives to those removing switches.

Other sources of mercury in the environment — primarily the burning of coal in power plants — remain to be addressed, and are a source of great contention between the utility industry, the Bush administration and environmentalists. But the removal of mercury switches before they can poison the environment is a big win for the American people, and a reason to celebrate.

Fred Krupp is president of Environmental Defense, New York City, and Mike Garfield is director of Ecology Center, Berkeley, Calif.