1. National Exposure Research Laboratory, US Environmental Protection Agency, 26 W. Martin Luther King Drive, Cincinnati, Ohio 45268 USA
2. Department of Fisheries and Wildlife, Oregon State University, ℅ US Environmental Protection Agency, 200 SW 35th Street, Corvallis, Oregon 97333 USA
3. Department of Biology, University of Louisville, Louisville, Kentucky 40292 USA
4. OAO Corporation, ℅ US Environmental Protection Agency, 200 SW 35th Street, Corvallis, Oregon 97333 USA