State officials say exposure to the chemical can cause dizziness, watery eyes, difficulty breathing, headaches and liver problems.
About 275 toddlers and children have been moved to another preschool while workers clean the building.
State officials have been monitoring air quality in the building since July 2007. That's when officials ordered a statewide review of child-care centers near contaminated sites.
Tests conducted last month showed the elevated levels.
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