"NATRONA HEIGHTS, Pa. -- On crisp fall mornings in the Allegheny River valley, the fog that hangs over Highlands High School usually burns off by the first bell. What remains in the air is the question.

Almost a year after tests by USA TODAY found significant levels of two potentially toxic metals in the air outside the school, local health officials expanded their own monitoring efforts here. The reason: Air samples taken by the county earlier this year showed even higher levels of the metals than what USA TODAY found -- on two days, at least nine times more.

Highlands, flanked by two metals plants, is among scores of schools where regulators -- local, state or federal -- are monitoring outdoor air for toxic chemicals, many that pose unique dangers to kids. The monitoring is not required by law but came in response to the USA TODAY investigation that identified hundreds of schools where chemicals from nearby industries may permeate the air."

Blake Morrison and Brad Heath report for USA TODAY September 14, 2009. [2]