State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu 210023, PR China.
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, Jiangsu 210008, PR China.
Chemosphere. 2019 Jul;226:94-102. doi: 10.1016/j.chemosphere.2019.03.082. Epub 2019 Mar 19.
Fe(III)-bearing clay minerals are ubiquitous in the environment. However, the fate of organic contaminants mediated by structural Fe(III) in clays was rarely reported. Here we demonstrated that hydroxylated polychlorinated diphenyl ethers (HO-PCDEs) could be spontaneously formed from the reaction of 2,4,6-trichlorophenol (2,4,6-TCP) with three native smectites: SWy-2, NAu-1, and NAu-2. Further research demonstrated that the structural Fe(III) in smectite is indispensable for the mediation of 2,4,6-TCP to produce chlorophenoxy radical for the subsequent dimerization. The reaction is highly dependent on the relative humidity of the system and the site occupancy of structural Fe(III). Active structural Fe(III) in NAu-2 that played a significant role in the dimerization reaction is relatively more distorted, which would interact strongly with 2,4,6-TCP under low humidity and be inhibited by water molecules. Hence reaction on NAu-2 is suppressed as relative humidity increases. Whereas, water molecules would reduce the activation and reaction energies via forming a hydrogen bond with reaction intermediates, thus enhancing the reactions on SWy-2 and NAu-1 with less water sensitive structural Fe(III). Considering the wide distribution of Fe(III)-bearing smectites in the environment, the contribution of structural Fe(III) for the formation of more toxic dioxin-like compounds from chlorophenols might need to be taken into consideration to evaluate their potential environmental risks.
含三价铁的粘土矿物在环境中无处不在。然而，粘土矿物中结构三价铁介导的有机污染物的命运却很少被报道。在这里，我们证明了，来自 2,4,6-三氯苯酚（2,4,6-TCP）与三种天然蒙脱石（SWy-2、NAu-1 和 NAu-2）的反应，可以自发形成羟基化多氯二苯醚（HO-PCDEs）。进一步的研究表明，蒙脱石中结构三价铁对于介导 2,4,6-TCP 生成氯苯氧自由基以进行后续二聚化是不可或缺的。该反应高度依赖于系统的相对湿度和结构三价铁的位置占有率。在二聚化反应中起重要作用的 NAu-2 中活性结构三价铁相对更扭曲，在低湿度下会与 2,4,6-TCP 强烈相互作用，并被水分子抑制。因此，随着相对湿度的增加，反应受到抑制。然而，水分子会通过与反应中间体形成氢键来降低活化能和反应能，从而增强在 SWy-2 和 NAu-1 上的反应，这些反应对结构三价铁的水敏感性较低。考虑到环境中含三价铁的蒙脱石的广泛分布，结构三价铁对氯酚形成更具毒性的类二恶英化合物的贡献可能需要被考虑，以评估它们的潜在环境风险。
