1. Institute of Hygiene and Environmental Medicine, RWTH Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany, Institute and Out-patient Clinic for Occupational Medicine, RWTH Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany, Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, D-30625 Hannover, Germany, and Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland