1. Institute for Science and Technology in Medicine, Keele University, Stoke–on–Trent ST4 7QB, UK
2. Molecular Toxicology Division, School of Biology, University of Nottingham, Nottingham NG7 2RD, UK
3. Centre for Environmental Magnetism and Palaeomagnetism, Geography Department, Lancaster University, Bailrigg, Lancaster LA1 4YW, UK
4. Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK