1. Stable Isotope and Radiocarbon Unit, Institute of Nanoscience and Nanotechnology, National Centre for Scientific Research (N.C.S.R.) “Demokritos”, Attiki , Greece
2. Department of Animal and Human Physiology, Faculty of Biology, School of Sciences, University of Athens, Athens , Greece
3. School of Geology, Faculty of Sciences, Aristotle University of Thessaloniki, Thessaloniki , Greece