Some California classrooms may be contaminated, and not with the cooties. According to a new state study, portable classrooms are more likely than their conventional counterparts to contain dangerous levels of toxic chemicals. Half of the portable classrooms studied exceeded air-quality guidelines for eight-hour indoor exposure to formaldehyde, and one-hour exposure levels were 10 times more likely to exceed federal guidelines than regular classrooms. Formaldehyde, which is found in pressed-wood furniture, wallboard, and carpeting, is a carcinogen and can cause respiratory and immune-system problems. Because of growing enrollment levels and shrinking budgets, portable classrooms are becoming increasingly common in California; they account for one-third of state classrooms, and some 2 million students spend at least part of their day in them. A lawsuit filed in 2000 convinced manufacturers of prefab classrooms to switch to a less toxic form of formaldehyde and increase ventilation, but the improvements only apply to the most recently purchased portables.