1 Institute of Nanoproduct Safety Research, Hoseo University, Asan 336-795, Republic of Korea.
2 Toxicology Department, National Institute for Occupational Health, Johannesburg 2001, South Africa ; Haematology and Molecular Medicine Department, The University of the Witwatersrand, 25 Hospital Street, Constitution Hill, Johannesburg 2001, South Africa.
3 Green Nanotechnology Center, School of Mechanical Engineering, Korea University, Seoul 136-701, Republic of Korea.
4 Nanoscale Characterization & Environmental Chemistry Laboratory, Department of Chemistry, Hanyang University, Seoul 133-791, Republic of Korea.
5 Department of Health and Human Services, National Institute for Occupational Safety and Health, 395 E Street, SW, Patriots Plaza 1, Suite 9200, Washington, DC 20201, USA.