A macroporous and macromolecular product, in bead form, polystyrene cross-linked by divinylbenzene, containing pendant N-chlorosulfonamide groups, was used to oxidize nitrite to nitrate in dilute aqueous alkaline, neutral, or acidic media. The well-known sodium salt of this macromolecular oxidant was unreactive in the said conditions; however, its hydrogen form was very reactive and enabled it to complete nitrite elimination. Nitrates in wastewaters are a few hundred times less harmful than nitrites. Aqueous solutions of nitrates at the concentration in question can serve as a nutritive spray for farmlands.