1. Institute of Environmental Medicine, Karolinska Institutet, Stockholm 171 77, Sweden
2. Division of Occupational and Environmental Medicine, Department of Laboratory Medicine, Lund University, Lund 223 63, Sweden
3. Centre for Occupational and Environmental Medicine (CAMM), Stockholm County Council, Stockholm 113 65, Sweden
4. Section of Occupational and Environmental Medicine, Sahlgrenska Academy at University of Gothenburg, Gothenburg 405 30, Sweden