Solvents

The air at a North Bronx school may have been contaminated by dangerous chemicals for as long as 20 years.

Officials closed the Bronx New School at 3200 Jerome Ave. after repeated air monitoring tests since January revealed unsafe levels of several toxic chemicals, especially trichloroethylene (TCE), which is a possible carcinogen.

Until three years ago, public health officials thought that when they had cleaned up spilled toxic solvents in the ground, their work was done. But then they learned about "vapor intrusion."

That is a process where the remaining traces of contaminants -- such as tetrachloroethylene -- form a gas that migrates through the soil into adjacent structures, creating a health hazard. Some of the chemicals are known carcinogens and others could create other health problems.