1. Department of Public Health, Section of Environmental Health, University of Copenhagen, Øster Farimagsgade 5A, DK-1014 Copenhagen K, Denmark
2. The National Research Centre for the Working Environment, Lersø Parkalle 105, DK-2100 Copenhagen Ø, Denmark
3. Department of Occupational and Environmental Medicine, Sahlgrenska Academy at University of Gothenburg, 40530 Gothenburg, Sweden