The conference was jointly sponsored by the European Commission, the German Ministry for the Environment, Nature Conservation and Nuclear Safety and the Ministry of the Environment and Transport of the State of Baden- Württemberg, and organised by the Federal Environmental Agency. We are very grateful to the chairpersons of the several sessions and, last but not least, to all participants for their contributions which made the conference a place for very interesting discussions. We apologise to those who could not participate in the conference because it was fully booked, and hope that these conference proceedings will give them and all other interested people a good overview of the conference.