Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.
Environ Sci Technol. 2012 Nov 6;46(21):11635-43. doi: 10.1021/es3015277. Epub 2012 Oct 17.
Aqueous chlorine solutions (defined as chlorine solutions (Cl(2,T)) containing solely or a combination of molecular chlorine (Cl(2)), 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 (ClO(4)(-)) production-a well-known thyroid hormone disruptor- from stored bleach solutions indicates the presence of unexplored transformation pathway(s). The evaluation of this potential ClO(4)(-) source is important given the widespread use of aqueous chlorine as a disinfectant. In this study, we perform detailed rate analysis of ClO(4)(-) 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 ClO(4)(-) 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 of ClO(4)(-) produced depends on the starting concentrations of Cl(2,T) and ClO(3)(-), 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 ClO(3)(-) to produce ClO(4)(-) with calculated rate coefficient (k(ClO4-)) of (4-40) × 10(5) M(-1) s(-1) and (3-250) × 10(5) M(-1) s(-1) for UV-B/C and UV-A, respectively. The measured ClO(4)(-) concentrations for both UV-B and UV-C experiments agreed well with our model (R(2) = 0.88-0.99), except under UV-A light exposure (R(2) = 0.52-0.93), 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 ClO(4)(-) concentrations (~0.1 μg L(-1)) much below the proposed drinking water limits. The importance of the hypothesized mechanism is discussed in relation to natural ClO(4)(-) formation by atmospheric transformations.
含氯水溶液（定义为仅含有或组合有分子氯（Cl2，T）、次氯酸（HOCl）和次氯酸盐（OCl-）的氯溶液）通过光激活转化已知会产生有毒的无机消毒副产物（例如，氯酸盐和亚氯酸盐）。最近有报道称，从储存的漂白剂溶液中产生高氯酸盐（ClO4-）-一种众所周知的甲状腺激素干扰物-表明存在未探索的转化途径。鉴于含氯水溶液被广泛用作消毒剂，评估这种潜在的 ClO4-来源非常重要。在这项研究中，我们在不同的环境条件下（包括紫外线（UV）光源、强度、溶液 pH 值和 Cl2，T 浓度）对含氯水溶液中 ClO4-的生成进行了详细的速率分析。我们的结果表明，在含氯水溶液暴露于 UV 光下会产生 ClO4-，在所有实验条件下，产率范围为 0.09×10-3%至 9.2×10-3%。产生的 ClO4-的量取决于 Cl2，T 和 ClO3-的起始浓度、UV 源波长和溶液 pH 值，但与光强度无关。我们假设了一个由 Cl2，T 光分解的已知反应衍生而来的机制途径，该途径涉及 Cl 自由基与 ClO3-的反应，生成 ClO4-，计算得到的速率系数（k（ClO4-））为（4-40）×105 M-1 s-1和（3-250）×105 M-1 s-1，分别用于 UV-B/C 和 UV-A。对于 UV-B 和 UV-C 实验，测量到的 ClO4-浓度与我们的模型非常吻合（R2=0.88-0.99），除了在 UV-A 光照射下（R2=0.52-0.93），这表明在较高波长下可能涉及其他途径。基于我们的结果，与饮用水处理相关浓度的含氯水溶液的光转化将导致 ClO4-浓度（~0.1μg L-1）远低于提议的饮用水限值。所假设的机制的重要性与大气转化产生的天然 ClO4-形成有关。
