1. a U.S. EPA, National Exposure Research Laboratory , Research Triangle Park , North Carolina , USA
2. b U.S. EPA, National Health and Environmental Effects Research Laboratory , Chapel Hill , North Carolina , USA
3. c Centers for Disease Control, Division of Environmental Health Laboratory Sciences , Atlanta , Georgia
4. d ManTech Environmental Technology , Research Triangle Park , North Carolina , USA
5. e U.S. EPA, National Exposure Research Laboratory , Research Triangle Park , North Carolina , USA