1. U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, 26 West Martin Luther King Drive, MS 564, Cincinnati, Ohio 45268
2. U.S. Geological Survey, National Water Quality Laboratory, P.O. Box 25046, MS 407, Denver Federal Center, Building 95, Denver, Colorado 80225
3. U.S. Geological Survey, 400 S. Clinton Street, Room 269, Federal Building, Iowa City, Iowa 52244
4. U.S. Geological Survey, Organic Geochemistry Research Laboratory, 4821 Quail Crest Place, Lawrence, Kansas 66049
5. U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, D305-01, Research Triangle Park, North Carolina 27711