Department of Chemistry, The University of Memphis, Memphis, TN 38152, USA.
Molecules. 2021 Jun 4;26(11):3411. doi: 10.3390/molecules26113411.
In January 2014, over 10,000 gallons of methyl-cyclohexane methanol (MCHM) leaked into the Elk River in West Virginia, in a chemical spill incident that contaminated a large portion of the state's water supply and left over 300,000 residents without clean water for many days and weeks. Initial efforts to remove MCHM at the treatment plant centered on the use of granulated activated carbon (GAC), which removed some of the chemical from the water, but MCHM levels were not lowered to a "non-detect" status until well after the chemical plume had moved downstream of the intake. Months later, MCHM was again detected at the outflow (but not the inflow) at the water treatment facility, necessitating the full and costly replacement of all GAC in the facility. The purpose of this study is to investigate the hypothesis that preferential absorbance of one of the two MCHM isomers, coupled with seasonal variations in water temperature, explain this contrary observation. Calculated intermolecular potentials between ovalene (a large planar polycyclic aromatic hydrocarbon) and the MCHM isomers were compared to physisorption potentials of MCHM onto an amorphous carbon model. While a molecular mechanics (MM) force field predicts no difference in the average interaction potentials between the - and -MCHM with the planar ovalene structure, MM predicts that the isomer binds stronger than the isomer to the amorphous carbon surface. Semi-empirical and density functional theory also predict stronger binding of -MCHM on both the planar and amorphous surfaces. The differences in the isomer binding strengths on amorphous carbon imply preferential absorbance of the isomer onto activated charcoal filter media. Considering seasonal water temperatures, simple Arrhenius kinetics arguments based on these predicted binding energies help explain the environmental observations of MCHM leeching from the GAC filters months after the spill. Overall, this work shows the important implications that can arise from detailed interfacial chemistry investigations.
2014 年 1 月，超过 10000 加仑的甲基环己烷甲醇（MCHM）在西弗吉尼亚州的埃尔克河发生化学泄漏事件中泄漏，污染了该州大部分的供水系统，导致超过 30 万居民数日乃至数周没有干净的水。最初在处理厂清除 MCHM 的工作集中在使用颗粒状活性炭（GAC）上，这从水中去除了一些化学物质，但直到化学羽流向下游移动到进水口之后，MCHM 的水平才降低到“未检出”状态。几个月后，在水处理设施的流出物（而不是流入物）中再次检测到 MCHM，这需要在设施中完全更换所有 GAC。本研究的目的是调查以下假设：两种 MCHM 异构体之一的优先吸收，加上水温的季节性变化，解释了这一相反的观察结果。计算了椭圆烯（一种大的平面多环芳烃）与 MCHM 异构体之间的分子间势能，并将 MCHM 对无定形碳模型的物理吸附势能进行了比较。虽然分子力学（MM）力场预测在与平面椭圆烯结构的平均相互作用势能之间，-和 -MCHM 之间没有差异，但 MM 预测 -异构体与无定形碳表面的结合强度大于 异构体。半经验和密度泛函理论也预测 -MCHM 在平面和无定形表面上的结合强度更强。无定形碳上异构体结合强度的差异表明，-异构体优先被吸附到活性炭过滤介质上。考虑到季节性水温，基于这些预测结合能的简单阿伦尼乌斯动力学论点有助于解释泄漏数月后从 GAC 过滤器中渗出 MCHM 的环境观察结果。总的来说，这项工作表明，从详细的界面化学研究中可以得出重要的结论。
