Perchlorate Production by Photodecomposition of Aqueous Chlorine Solutions

Aqueous chlorine solutions (defined as chlorine solutions (Cl2,T) containing solely or a combination of molecular chlorine (Cl2), hypochlorous acid (HOCl), and hypochlorite (OCl–)) are known to produce toxic inorganic disinfection byproduct (e.g., chlorate and chlorite) through photoactivated transformations. Recent reports of perchlorate (ClO4–) production—a well-known thyroid hormone disruptor— from stored bleach solutions indicates the presence of unexplored transformation pathway(s). The evaluation of this potential ClO4– source is important given the widespread use of aqueous chlorine as a disinfectant. In this study, we perform detailed rate analysis of ClO4– generation from aqueous chlorine under varying environmental conditions including ultraviolet (UV) light sources, intensity, solution pH, and Cl2,T concentrations. Our results show that ClO4– is produced upon UV exposure of aqueous chlorine solutions with yields ranging from 0.09 × 10–3 to 9.2 × 10–3% for all experimental conditions. The amount...