Freitas, M.C., C. Andrade, A. Cruces, J. Munhá, M. J. Sousa, S. Moreira, J. M. Jouanneau, and L. Martins. “Anthropogenic influence in the Sado estuary (Portugal): a geochemical approach”. Journal of Iberian Geology, vol. 34, vol. 34, no. 2, 2008, pp. 271-86, https://revistas.ucm.es/index.php/JIGE/article/view/JIGE0808220271A.