In this study we reveal the capacity of imidacloprid (a neonicotinoid insecticide) to photoinduce nitration and nitrosation of three aromatic probes (phenol, resorcinol, tryptophan) in water. Using a gas-flow reactor and NOx analyzer, the production of gaseous NO/NO2 was demonstrated during irradiation (300-450 nm) of imidacloprid (10-4 M). Quantum calculations showed that formation of NOx 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 be ranging between 0.08% and 5.1%. The contribution of NO3-/NO2- to the nitration and nitrosation processes was found minor under our experimental conditions. In contrast, the addition of natural organic matter (NOM) enhanced significantly the yields of nitro/nitroso derivatives, likely via production of triplet excited states (3NOM*) and HO.. These findings reveal the importance of investigating the photochemical reactivity of water contaminants in mixture to better understand the cocktail effects on their fate and toxicity.