As mercury (search) spills in schools disrupt classes, teachers and environmental groups want to rid student labs of the versatile but dangerous metal.

In recent weeks, mercury was found in stairwells and corridors of a high school in the nation's capital. The building had to be closed twice for decontamination and still more traces were found Sunday even as cleaning crews were wrapping up their work in preparation for reopening the school Monday.

"We're shocked," District of Columbia Public Schools spokeswoman Leonie Campbell said.

The building would be closed again Monday, school officials announced. They were searching for an alternate location to hold classes.

Although the spills get headlines, the use of mercury in schools actually is declining, said Ken Roy, a physics teacher in Glastonbury, Conn., and co-chairman of the National Science Teachers Association's safety advisory board.

"The awareness is so high now that I would say a good part of it (mercury) is gone from schools," Roy said. "The problem comes when a teacher retires, and someone new comes in and finds a horde of it in a cabinet in a chemical storeroom. You've got to dig for it."

In its elemental form, mercury is shiny, silver and odorless. It is the only metal on earth that is liquid at room temperature.

In schools, mercury is found in fever thermometers, electronic light switches and other basic equipment. It is most common in science labs, where mercury-filled instructional tools have been used for decades.

But the fascination with small beads of mercury has given way to talk of their potential risks.

Mercury turns into a problem when it is spilled and evaporates into airborne vapors, which can be absorbed into the body through breathing.

Exposure to high levels of metallic mercury can damage the brain, kidneys and lungs. Prolonged exposure to lower levels can cause problems with sleep, sight, hearing and memory, according to the federal Agency for Toxic Substances and Disease Registry.

The Environmental Protection Agency has encouraged schools to remove mercury compounds and mercury-containing equipment. The agency is helping schools get rid of those materials.

At least nine states have created programs to speed up the removal of mercury from schools through lab clean-outs and educational outreach to teachers, the EPA says.

Schools are finding safe alternatives, such as electronic thermometers in place of mercury ones, and generally have not reduced their science labs, Roy said. "If anything, more lab activities are being done," he said. "Professional safety training is the key here."

Mercury is required to be safely secured as a hazardous material, Roy said. But some students have taken possession of it at school or at home and caused a health scare.

No firm statistics on all mercury spills at schools are available, federal officials say.

But the number of reported spills in schools is on the rise, according to the EPA. The agency responded to 12 emergency removals in 2004, with cleanup costs as high as $200,000.

Since late February, mercury has been detected twice at Cardozo Senior High School in the District of Columbia, forcing the closing of the building for decontamination. Officials were planning to reopen the facility Monday, but mercury was found for a third time late Sunday.

In 2003, mercury stolen from a science lab ended up being spread throughout Ballou High School, also in the capital. The school was closed for 35 days, with cleanup costs of $1.5 million, the EPA said.

Since then, the city's school system has banned mercury from its buildings.

Over the past few years, reports of mercury spills have come from schools in Arizona, Kentucky, Michigan, Massachusetts, Mississippi and Nevada.

"I don't think there was the general knowledge of the health hazards of mercury that we have today," said John Risher, mercury chemical manager for the Agency for Toxic Substances and Disease Registry. "A lot of information was there, it just wasn't widely disseminated."