A new insight into ethoxyquin fate in surface waters: Stability, direct and indirect photochemical behaviour and the identification of main products

• We investigated the photochemical fate of ethoxyquin.
• The lifetime of ethoxyquin in surface waters was estimated to be less than 1 min.
• The transformation of ethoxyquin is strongly enhanced under UVB radiation.

In this work, the fate of ethoxyquin (ETX), an antioxidant used as a food preservative and a pesticide, is investigated under ultraviolet and visible irradiation. The fast photolysis observed under environmentally closed conditions results in estimated degradation rates (RETXd) of 1.6 × 10−8 and 8.7 × 10−7 M s−1 at pH 2.7 and 8.0, respectively. Under our experimental conditions, the polychromatic quantum yield (φETX) is evaluated to be 5.0 × 10−3 and 1.4 × 10−1 for the protonated and anionic forms of ETX, respectively. The effect of hydroxyl radical on ETX degradation is evaluated, and the degradation kinetics profiles suggest that transformation via hydroxyl radical can be neglected compared with direct photolysis. Structures for the main degradation products (hydrolysis, photochemical and HO- mediated derivative) are proposed. The kinetic parameters are used as inputs in APEX software to model the degradation of ETX as a function of different scenarios in surface waters. Finally, the irradiation of ETX under sun-simulated conditions estimates the life of this compound to be ∼38 s.