G. R. de Castro, C. do C. F. Padilha, J. C. Rocha, J. P. S. Valente, A. de O. Florentino, and P. M. Padilha, “Lability of Cd, Cr, Cu, Mn and Pb complexed by aquatic humic substances”, Eclet. Quim., vol. 30, no. 2, pp. 45–51, Jun. 2005.