Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University , Columbus, Ohio 43210, United States.
Department of Biology, Juniata College , Huntingdon, Pennsylvania 16652, United States.
Environ Sci Technol. 2017 Dec 5;51(23):13985-13994. doi: 10.1021/acs.est.7b01539. Epub 2017 Nov 13.
Hydraulic fracturing fluids are injected into shales to extend fracture networks that enhance oil and natural gas production from unconventional reservoirs. Here we evaluated the biodegradability of three widely used nonionic polyglycol ether surfactants (alkyl ethoxylates (AEOs), nonylphenol ethoxylates (NPEOs), and polypropylene glycols (PPGs)) that function as weatherizers, emulsifiers, wetting agents, and corrosion inhibitors in injected fluids. Under anaerobic conditions, we observed complete removal of AEOs and NPEOs from solution within 3 weeks regardless of whether surfactants were part of a chemical mixture or amended as individual additives. Microbial enzymatic chain shortening was responsible for a shift in ethoxymer molecular weight distributions and the accumulation of the metabolite acetate. PPGs bioattenuated the slowest, producing sizable concentrations of acetone, an isomer of propionaldehyde. Surfactant chain shortening was coupled to an increased abundance of the diol dehydratase gene cluster (pduCDE) in Firmicutes metagenomes predicted from the 16S rRNA gene. The pduCDE enzymes are responsible for cleaving ethoxylate chain units into aldehydes before their fermentation into alcohols and carboxylic acids. These data provide new mechanistic insight into the environmental fate of hydraulic fracturing surfactants after accidental release through chain shortening and biotransformation, emphasizing the importance of compound structure disclosure for predicting biodegradation products.
水力压裂液被注入页岩中，以扩展裂缝网络，从而提高非常规储层的石油和天然气产量。在这里，我们评估了三种广泛使用的非离子聚乙二醇醚表面活性剂（烷基聚氧乙烯醚（AEOs）、壬基酚聚氧乙烯醚（NPEOs）和聚丙二醇（PPGs））的可生物降解性，这些表面活性剂在注入液中用作调湿剂、乳化剂、润湿剂和缓蚀剂。在厌氧条件下，我们观察到 AEOs 和 NPEOs 无论是否作为化学混合物的一部分存在或作为单独的添加剂添加，都能在 3 周内从溶液中完全去除。微生物酶促链缩短导致乙氧基摩尔分子量分布的变化和代谢物乙酸的积累。PPGs 的生物衰减最慢，产生大量丙酮，丙醛的一种异构体。表面活性剂链缩短与厚壁菌门宏基因组中二醇脱水酶基因簇（pduCDE）的丰度增加有关，该宏基因组是从 16S rRNA 基因预测得到的。pduCDE 酶负责在乙氧基链单元发酵成醇和羧酸之前将其裂解成醛。这些数据为水力压裂液表面活性剂在意外释放后通过链缩短和生物转化的环境归宿提供了新的机制见解，强调了化合物结构披露对于预测生物降解产物的重要性。
