Natural formation of nitrophenols in sunlit water containing nitrite and natural organic matter

Nitroaromatic compounds are environmental contaminants that are classically attributed to an anthropogenic origin. On the contrary, we hypothesized that nitrophenolic compounds could be formed by reaction of natural organic matter and nitrite ( NO2-) in sunlit waters. We exposed water samples containing natural organic matter and nitrite to natural sunlight and arti-ficial ultraviolet irradiation. Results show the formation 6.6 nM of 4-nitrophenol and 33.6 nM of 3-nitro-4-hydroxybenzoic acid after 28 h under natural sunlight with 0.3 mM of nitrite. This formation was accelerated with ultraviolet light or with increasing nitrite levels. This formation is explained by the reaction of nitrogen dioxide radical ( NO2 center dot ), generated by nitrite photolysis, with phenolic moieties in natural organic matter macromolecules via H-abstraction, generating phenoxyl radicals which couple with another nitrogen dioxide radical to generate nitrophenolic compounds. Overall, the natural contribution of nitrophenolic compounds has been probably overlooked in the environment.