The authors thank Jorge Millos (CACTI, University of Vigo) for his help in the isotope ratio measurements by MC-ICP-MS. ISC-SCIENCE and all participant laboratories are acknowledged for their contribution. J. A. Rodríguez-Castrillón is grateful to the Ministry of Education and Science (MEC, Madrid, Spain) for his pre-doctoral fellowship. M. Moldovan thanks the European Social Fund and the MEC for the funding through the ‘‘Juan de la Cierva’’ Programme. Financial support from CICYT through projects BQU2003-03438 and CTQ2006-05722 is gratefully acknowledged.