Iron oxide magnetic nanoparticles (Fe3O4 MNPs) can effectively activate persulfate anions (S2O82-) to produce sulfate free radicals (SO4 center dot-), which are a powerful oxidant with promising applications to degrade organic contaminants. The kinetics of sulfamonomethoxine (SMM) degradation was studied in the system of Fe3O4 MNPs and S2O82-. A complete removal of the added SMM (0.06 mmol L-1) was achieved within 15 min with the addition of 1.20 mmol L-1 s(2)O(8)(2-) and 2.40 mmol L-1 Fe3O4 MNPs. There is an optimum concentration of Fe3O4 MNPs because Fe3O4 MNPs may also act as a SO4 center dot- scavenger at higher concentrations. It was further observed that the addition of Fe3O4 MNPs in several batches for a given total amount of the activator is favorable to enhancing the degradation of SMM. A degradation mechanism was proposed on the basis of identification of the degradation intermediates of SMM with liquid chromatography combined with mass spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.