BACKGROUND: Dinitrotoluenes (DNTs) are environmentally persistent, making the remediation of contaminated streams and groundwater difficult. Zero-valent iron (Fe-0) can be used as an electron source for the reduction of recalcitrant DNTs in waste-water and thus enhance their biodegradability. However, little is known about the qualitative effects of major anions and cations present in waste-water on the reduction of DNTs by Fe-0. RESULTS: The presence of Na2SO4 and NaCl at levels between 0.25 and 2 mmol L-1 was observed to enhance the reactivity of Fe-0 towards 2,4-DNT. The positive effect of K2SO4 is stronger than that of Na2SO4 at the same level (1 mmol L-1). Varying (NH4)(2)SO4 from 0.1 to 1.0 mmol L-1 improved the efficiency of 2,4-DNT degradation by Fe-0. The effects of varying NaNO3 and NaNO2 from 0 mmol L-1 to 4.7 mmol L-1 and 0 mmol L-1 to 5.8 mmol L-1, respectively, were also investigated. Both NaNO3 and NaNO2 at low concentration improved the efficiency of 2,4-DNT degradation by Fe, however, at high concentration, inhibiting effects appeared. CONCLUSION: SO42-, Cl-, Na+, K+ and NH4+ notably enhanced 2,4-DNT reduction by Fe-0 at the tested concentrations. The positive effect of K+, Cl- was relatively stronger than that of Na+ and sulfate (SO42-). However, the effect of NH4+ was relatively weaker at concentrations greater than 1.0 mmol L-1. The presence of low concentrations of NO3-and NO2- promoted 2,4-DNT reduction by Fe-0 and inhibited the reaction. The results suggest that 2,4-DNT reduction by Fe-0 can be controlled by the ions composition of the waste-water. (C) 2010 Society of Chemical Industry