[1] Univ N Carolina, Curriculum Toxicol, Chapel Hill, NC 27515 USA
[2] Univ N Carolina, Ctr Environm Med Asthma & Lung Biol, Chapel Hill, NC USA
[3] Univ N Carolina, Dept Pediat, Chapel Hill, NC USA
[4] US EPA, Natl Hlth & Environm Effects, Res Lab, Res Triangle Pk, NC 27711 USA