In this study, we
reveal the capacity of imidacloprid (a neonicotinoid
insecticide) to photoinduce the nitration and nitrosation of three
aromatic probes (phenol, resorcinol, and tryptophan) in water. Using
a gas-flow reactor and a NO
x
analyzer,
the production of gaseous NO/NO2 was demonstrated during
irradiation (300–450 nm) of imidacloprid (10–4 M). Quantum calculations showed that the formation of NO
x
proceeds via homolytic cleavage of the RN–NO2 bond in the triplet state. In addition to gaseous NO/NO2, nitrite and nitrate were also detected in water, with the
following mass balance: 40 ± 8% for NO2, 2 ±
0.5% for NO, 52 ± 5% for NO3
–, and
16 ± 2% for NO2
–. The formation
of nitro/nitroso probe derivatives was evidenced by high-resolution
mass spectrometry, and their yields were found to range between 0.08
and 5.1%. The contribution of NO3
–/NO2
– to the nitration and nitrosation processes
was found to be minor under our experimental conditions. In contrast,
the addition of natural organic matter (NOM) significantly enhanced
the yields of nitro/nitroso derivatives, likely via the production
of triplet excited states (3NOM*) and HO•. These findings reveal the importance of investigating the photochemical
reactivity of water contaminants in a mixture to better understand
the cocktail effects on their fate and toxicity.