1. Research Professor, Dept. of Environmental Science and Engineering, Ewha Womans Univ., Seoul, 120-750, South Korea (corresponding author).
2. Research Chemist, U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Ada, OK 74820.
3. Research Technician, U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Ada, OK 74820.