Heterogeneous photocatalysis of 1,3-dinitrobenzene (DNB) using simulated solar irradiation in the presence of semiconductor oxides was studied. Comparison of TiO2 and ZnO showed that the former was a more efficient photocatalyst for the degradation of DNB. The addition of potential environmental co-contaminants such as acetic acid, fulvic acid and seawater salts to the DNB solutions all inhibited the DNB degradation rate. The addition of hydroxyl radical-generating compounds, including H2O2 and NaNO3, to the DNB solutions both slightly reduced the DNB degradation rate, indicating that hydroxyl radical generation is not a rate limiting step in the overall reaction process. The use of 5 volume % acetone cosolvent slowed the degradation rate, however for 15 volume % acetone despite the slower relative rate of destruction, the higher concentrations of DNB provided higher mass destruction rates.