UVA irradiation induces direct phototransformation of 2,4-dinitrophenol in surface water samples.

Lake water samples spiked with 2,4-dinitrophenol (24DNP) were irradiated under artificial UVA irradiance. It was found that the direct photolysis is the main photodegradation pathway of 24DNP in lake water. On the lake water samples it was also determined the formation and consumption rates of *OH, by means of the transformation reaction of benzene into phenol. It was found that the rate of direct photolysis prevails over the *OH phototransformation rate by one-two orders of magnitude. Moreover, the excited triplet states of chromophoric dissolved organic matter and singlet oxygen are expected to play a negligible role in the photodegradation of 24DNP. By modelling the direct photolysis of 24DNP in surface water bodies, one gets a half-life time of 2-10 summer sunny days for water-column depths up to 10 m. This would make the direct photolysis a major pathway for the transformation of 24DNP in freshwaters.