Perchlorate Production by Photodecomposition of Aqueous Chlorine Solutions

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• 作者：Balaji Rao ; Nubia Estrada ; Shelly McGee ; Jerry Mangold ; Baohua Gu ; W. Andrew Jackson
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2012
• 出版时间：November 6, 2012
• 年：2012
• 卷：46
• 期：21
• 页码：11635-11643
• 全文大小：434K
• 年卷期：v.46,no.21(November 6, 2012)
• ISSN：1520-5851

文摘

Aqueous chlorine solutions (defined as chlorine solutions (Cl_2,T) containing solely or a combination of molecular chlorine (Cl₂), hypochlorous acid (HOCl), and hypochlorite (OCl^{鈥?/sup>)) are known to produce toxic inorganic disinfection byproduct (e.g., chlorate and chlorite) through photoactivated transformations. Recent reports of perchlorate (ClO₄鈥?/sup>) production鈥攁 well-known thyroid hormone disruptor鈥?from stored bleach solutions indicates the presence of unexplored transformation pathway(s). The evaluation of this potential ClO₄鈥?/sup> source is important given the widespread use of aqueous chlorine as a disinfectant. In this study, we perform detailed rate analysis of ClO₄鈥?/sup> generation from aqueous chlorine under varying environmental conditions including ultraviolet (UV) light sources, intensity, solution pH, and Cl_2,T concentrations. Our results show that ClO₄鈥?/sup> is produced upon UV exposure of aqueous chlorine solutions with yields ranging from 0.09 脳 10鈥? to 9.2 脳 10鈥?% for all experimental conditions. The amount of ClO₄鈥?/sup> produced depends on the starting concentrations of Cl_2,T and ClO₃鈥?/sup>, UV source wavelength, and solution pH, but it is independent of light intensity. We hypothesize a mechanistic pathway derived from known reactions of Cl_2,T photodecomposition that involves the reaction of Cl radicals with ClO₃鈥?/sup> to produce ClO₄鈥?/sup> with calculated rate coefficient (k_{ClO4鈥?/sub>) of (4鈥?0) 脳 105 M鈥? s鈥? and (3鈥?50) 脳 105 M鈥? s鈥? for UV-B/C and UV-A, respectively. The measured ClO4鈥?/sup> concentrations for both UV-B and UV-C experiments agreed well with our model (R2 = 0.88鈥?.99), except under UV-A light exposure (R2 = 0.52鈥?.93), suggesting the possible involvement of additional pathways at higher wavelengths. Based on our results, phototransformation of aqueous chlorine solutions at concentrations relevant to drinking water treatment would result in ClO4鈥?/sup> concentrations (0.1 渭g L鈥?) much below the proposed drinking water limits. The importance of the hypothesized mechanism is discussed in relation to natural ClO4鈥?/sup> formation by atmospheric transformations.}}