1. Department of Environmental Science and Management; Portland State University; P.O. Box 751 Portland Oregon 97207 USA
2. National Center for Environmental Assessment; U.S. Environmental Protection Agency; 1200 Pennsylvania Avenue, NW (8623P) Washington D.C. 20460 USA
3. National Health and Environmental Effects Research Laboratory; U.S. Environmental Protection Agency; 200 SW 35th Street Corvallis Oregon 97333 USA