Insights into the impacts of chloride ions on the oxidation of 2,4-dinitro- toluene using ferrous activated persulfate: Removal efficiency, reaction mechanism, transformation pathway, and toxicity assessment

Persulfate/Fe2+-based advanced oxidation processes are widely used to treat water contaminated with 2,4-dini-trotoluene (DNT). However, the oxidation of DNT by persulfate/Fe2+ in the presence of the chloride ion (Cl-) has not been addressed, and the transformation pathways and toxicities of the intermediate products remain unclear. In this study, the effect of different Cl- concentrations on the oxidation of DNT was investigated by persulfate/ Fe2+. After the addition of 1.0 mM Cl- and 6 h of oxidation, the removal efficiency of DNT increased by 68.5%. Scavenging experiments and an electron spin resonance analysis suggested that Cl- caused hydroxyl radicals to increase in content in the persulfate/Fe2+ system, thus promoting the removal of DNT. Eight intermediate products of DNT were accurately detected using high-resolution mass spectrometry, and the transformation pathways of DNT were proposed, including hydroxylation/oxidation, elimination of the nitro group, and chlo-rination process. The acute and chronic toxicities of the intermediate products decreased during the oxidation process, but chlorinated by-products posed a higher toxicological risk. This result is vital for the practical application and environmental safety evaluation of persulfate/Fe2+-based advanced oxidation.

Automated summary

In this study, the effect of chloride ion (Cl-) on the oxidation of 2,4-dinitrotoluene (DNT) by persulfate/Fe2+ was investigated. It was found that the presence of Cl- increased the content of hydroxyl radicals in the persulfate/Fe2+ system, leading to enhanced DNT removal. The transformation pathways of DNT were proposed, including hydroxylation/oxidation, elimination of the nitro group, and chlorination process. The toxicities of the intermediate products decreased during the oxidation process, but chlorinated by-products posed a higher toxicological risk.