1. Curriculum in Toxicology, University of North Carolina, Chapel Hill, North Carolina 27599
2. Experimental Pathology Laboratories, Inc., Research Triangle Park, North Carolina 27709
3. Environmental Carcinogenesis Division, National Health and Environmental Effects Research Laboratory (NHEERL), U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711
4. Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina 27599
5. Curriculum in Toxicology, University of North Carolina, Chapel Hill, North Carolina 27599, , Environmental Carcinogenesis Division, National Health and Environmental Effects Research Laboratory (NHEERL), U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711