1. Unit of Biomass Technology and Chemistry, Swedish University of Agricultural Sciences, P.O. Box 4097, SE-904 03 Umeå, Sweden
2. Environmental Chemistry, Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden, and Center for Musculoskeletal Research, National Institute for Working Life, P.O. Box 7654, SE−907 13 Umeå, Sweden