The authors are grateful for financial support from the Spanish Ministry of Economy and Competitiveness through Projects Ref. CTQ2009-12814 and Ref. CTQ2012-36711 (co-funded by FEDER). The UE is acknowledged for the provision of FEDER funds for the purchase of the MC-ICP-MS instrument. Oscar Galilea San Blas acknowledges his doctoral grant to the University of Oviedo, Spain.