One night in February, high school principal Matthew Smith got a frightening wake-up call.
The local fire department alerted him that the home of a student at Agua Fria High School was contaminated with liquid mercury that apparently had been taken from a science classroom. The next day, emergency crews descended on the school in haz-mat suits, discovering a toxic trail of mercury vapors in classrooms, locker rooms, and buses.
The high school, in Avondale, Ariz., was shut down for a week so it could be decontaminated. The homes of six students were tainted with mercury, two so severely that the families had to be relocated for 11 days, according to the Environmental Protection Agency. The total cleanup is expected to reach hundreds of thousands of dollars.
The mercury mess in Arizona was only the latest in thousands of incidents where children are exposed to elemental mercury, a poison that can damage the brain, trigger respiratory failure and cause other serious health problems.
Power plants are typically cast as the usual suspects of mercury contamination, since they emit mercury into the air, where it spreads globally. But many children are exposed to toxic levels of mercury much closer to home. Mercury spills inside schools and houses, often unreported, can release vapors into the air for weeks, even years.
Elemental mercury, or quicksilver, is a shiny, silvery liquid metal found in thermometers, thermostats, light bulbs, barometers and LCD screens. Though mercury inside these items poses little risk, once broken, they release mercury that vaporizes as an invisible, odorless gas.
Children are most frequently exposed to mercury when it is mishandled or improperly cleaned up after a spill. Broken thermometers, filled with tiny blobs of mercury, are the most common culprits.
From 2002 to 2006, more than 37,000 calls were made to U.S. poison control centers about children exposed to mercury. Of those, 30,891 concerned broken thermometers and 6,396 were caused by other sources, such as old science laboratories and religious or cultural ceremonies, according to a new report by the Agency for Toxic Substances and Disease Registry, part of the U.S. Centers for Disease Control and Prevention.
The report, released in February, was prompted by a number of high-profile incidents of children exposed to mercury, in particular, a 2004 case involving as many as 100 children in a thermometer-factory-turned-daycare center in New Jersey. U.S. Rep. Frank J. LoBiondo (R-New Jersey) commissioned the report.
"Basically there was concern that other types of events such as the one in New Jersey might be occurring throughout the U.S., so Congress directed ATSDR to do a review to look for events of elemental mercury exposures," said Robin Lee, an epidemiologist with ATSDR's Division of Health Studies and co-chair of the study.
Many science labs at schools, especially older ones, unknowingly house long-forgotten toxic chemicals such as mercury, chlorine gas and formaldehyde.
These chemical stockpiles are just accidents waiting to happen, which administrators at Agua Fria High found out the hard way on February 12. According to a police investigation, the source of the spill was five pounds of mercury stored in a medical bottle that a student took from an unlocked shelf in a science classroom.
"It was our understanding that there was no mercury available on campus to students at all," said principal Smith. "It was a learning experience for us and now we are really dotting our 'i's and crossing our 't's to make sure that there are no unsafe chemicals on this campus."
Other schools also have been forced to evacuate and shut down for days, sometimes even weeks, while emergency crews conduct expensive cleanups to remove dangerous levels of mercury.
At Ballou High School in Washington, D.C., in 2003, a student took liquid mercury from a science laboratory and sold some to other students. Mercury was found in the classrooms, gymnasium and cafeteria, and the school had to be shut down for 35 days to clean it up.