1. BGFA—Research Institute of Occupational Medicine, German Social Accident Insurance, Ruhr-University Bochum, Bürkle-de-la-Camp Platz 1, 44789 Bochum, Germany
2. Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Mailstop F53, Atlanta, GA 30341, USA