Institute of Geography, Ministry of Education Key Laboratory of Humid Subtropical Eco-geographical Process, Fujian Provincial Key Laboratory for Plant Eco-physiology, School of Geographical Sciences, Fujian Normal University, Fuzhou, Fujian 350007, China.
Institute of Geography, Ministry of Education Key Laboratory of Humid Subtropical Eco-geographical Process, Fujian Provincial Key Laboratory for Plant Eco-physiology, School of Geographical Sciences, Fujian Normal University, Fuzhou, Fujian 350007, China.
Water Res. 2024 Aug 1;259:121812. doi: 10.1016/j.watres.2024.121812. Epub 2024 May 23.
The environmental effects of biochar-derived organic carbon (BDOC) have attracted increasing attention. Nevertheless, it is unknown how BDOC might affect the natural attenuation of widely distributed chloroalkanes (e.g., 1,1,2,2-tetrachloroethane (TeCA)) in aqueous environments. We firstly observed that the kinetic constants (k) of TeCA dehydrochlorination in the presence of BDOC samples or their different molecular size fractions (<1 kDa, 1∼10 kDa, and >10 kDa) ranged from 9.16×10 to 26.63×10 Mh, which was significantly greater than the k (3.53×10 Mh) of TeCA dehydrochlorination in the aqueous solution at pH 8.0, indicating that BDOC samples and their different molecular size fractions all could promote TeCA dehydrochlorination. For a given BDOC sample, the kinetic constants (k) of TeCA dehydrochlorination in the initial pH 9.0 solution was 2∼3 times greater than that in the initial pH 8.0 solution due to more formation of conjugate bases. Interestingly, their DOC concentration normalized kinetic constants (k/[DOC]) were negatively correlated with SUVA, and positively correlated with A/A and the abundance of aromatic protein-like/polyphenol-like matters. A novel mechanism was proposed that the CH dipole of BDOC aliphatic structure first bound with the CCl dipole of TeCA to capture the TeCA molecule, then the conjugate bases (-NH-/-NH and deprotonated phenol-OH of BDOC) could attack the H atom attached to the β-C atom of bound TeCA, causing a CCl bond breaking and the trichloroethylene formation. Furthermore, a fraction of >1 kDa had significantly greater k/[DOC] values of TeCA dehydrochlorination than the fraction of <1 kDa because >1 kDa fraction had higher aliphiticity (more dipole-dipole sites) as well as more N-containing species and aromatic protein-like/polyphenol-like matters (more conjugate bases). The results are helpful for profoundly understanding the BDOC-mediated natural attenuation and fate change of chloroalkanes in the environment.
生物炭衍生有机碳 (BDOC) 的环境效应引起了越来越多的关注。然而，BDOC 如何影响广泛分布的氯代烷烃（例如 1,1,2,2-四氯乙烷（TeCA））在水相环境中的自然衰减尚不清楚。我们首先观察到，在 BDOC 样品或其不同分子量分数（<1 kDa、1∼10 kDa 和 >10 kDa）存在下，TeCA 脱氯化氢的动力学常数（k）范围为 9.16×10 至 26.63×10 Mh，明显大于 pH 8.0 时水溶液中 TeCA 脱氯化氢的 k（3.53×10 Mh），表明 BDOC 样品及其不同分子量分数都可以促进 TeCA 脱氯化氢。对于给定的 BDOC 样品，初始 pH 9.0 溶液中 TeCA 脱氯化氢的动力学常数（k）是初始 pH 8.0 溶液中的 2∼3 倍，这是由于更多共轭碱的形成。有趣的是，它们的 DOC 浓度归一化动力学常数（k/[DOC]）与 SUVA 呈负相关，与 A/A 和芳香族蛋白样/多酚样物质的丰度呈正相关。提出了一种新的机制，即 BDOC 脂肪族结构的 CH 偶极首先与 TeCA 的 CCl 偶极结合，捕获 TeCA 分子，然后 BDOC 的共轭碱（-NH-/-NH 和脱质子化的酚-OH）可以攻击结合的 TeCA 上β-C 原子上的 H 原子，导致 CCl 键断裂和三氯乙烯形成。此外，>1 kDa 分数的 TeCA 脱氯化氢的 k/[DOC]值明显大于<1 kDa 分数，因为>1 kDa 分数具有更高的脂肪性（更多偶极-偶极位点）以及更多的含氮物种和芳香族蛋白样/多酚样物质（更多的共轭碱）。这些结果有助于深刻理解 BDOC 介导的氯代烷烃在环境中的自然衰减和命运变化。
