Sulfonated aromatic pollutants such as 1,5-naphthalenedisulfonic acid (NDS or Armstrong's acid) are persistent compounds and thus resist environmental breakdown and microbial treatment. This study investigated the photo-oxidative degradation of such a persistent polar pollutant in the absence and presence of H2O2. The degradation of aqueous NDS solutions by photolysis was found to be efficient only in the presence of H2O2. The combination of UV irradiation and H2O2 leads to progressive degradation of NDS, which is converted into new, more biodegradable and non-toxic species.