1. Department of Environmental Toxicology, The Institute of Environmental and Human Health, Texas Tech University, P.O. Box 41163, Lubbock, Texas, 79409-1163, The Institute of Environmental and Human Health Field Station, Jeffersonian Institute, P.O. Box 764, Jefferson, Texas, 75657, Department of Biological Sciences, Biology Building, Texas Tech University, Lubbock, Texas, 79409-43131, and TraceAnalysis, Incorporated, 6701 Aberdeen Avenue, Lubbock, Texas, 79424