Formation of nitrophenolic byproducts in soils subjected to sulfate radical oxidation

Activated persulfate oxidation is an emerging technology with great prospects for soil remediation. For the first time, the present study demonstrated that application of this technology to soils with nitrite (NO 2 − ) presence yielded nitrophenolic byproducts, including 3-nitrophenol, 4-nitrophenol, 2-hydroxy-5-nitrobenzoic acid, and 4-hydroxy-3-nitrobenzoic acid. Their yields were positively related to the contents of soil organic matter (SOM). Most of these byproducts were distributed in soil waters, suggesting that they are readily transported to other places, thus can contaminate a larger area. Nitrated byproducts presumably formed by oxidation of NO 2 − by SO 4 − , which generates NO 2 . This generated NO 2 then reacted with phenolic moieties in SOM and was transformed to organic nitrogen. In addition, ammonia nitrogen in soils was oxidized by SO 4 − and contributed to the formation of nitrophenolic byproducts. Considering the omnipresence of nitrite and ammonia in subsurface soils, this study identified potential risks of persulfate use for in situ soil remediation. These results are relevant to devise strategies to avoid inappropriate use of oxidative reagents and the resulting formation of toxic byproducts.