1. Department of Occupational and Environmental Health, College of Public Health, University of Iowa, Iowa City, Iowa 52242, Department of Environmental Chemistry and Technology, University of Silesia, Szkolna 9, 40-006 Katowice, Poland, Department of Civil and Environmental Engineering, University of Iowa, Iowa City, Iowa 52242, and Graduate Center for Toxicology, University of Kentucky, Lexington, Kentucky 40546