Pires, A.M.M. et al. 2007. Organic acids in the rhizosphere and phytoavailability of sewage sludge-borne trace elements. Pesquisa Agropecuaria Brasileira. 42, 7 (Jul. 2007), 917–924. DOI:https://doi.org/10.1590/S1678-3921.pab2007.v42.7648.