ACCUMULATION OF SHORTER ETHOXYLATE CHAIN LENGTHS DURING ANAEROBIC BIODEGRADATION OF NONYLPHENOL ETHOXYLATE SURFACTANTS USED IN HYDRAULIC FRACTURING FLUIDS

New techniques for stimulating and completing oil and gas wells, including the methods of horizontal drilling and hydraulic fracturing, have significantly improved the production of hydrocarbon resources from low permeable shale formations in the United States. However, since the application of these techniques at large scales is relatively novel, there is much to be discovered regarding their efficacy and environmental footprint. Surfactants make up a large portion of the organic additives in hydraulic fracturing fluids and are increasingly being used by industry for multiple purposes. This research targets a specific group of nonionic surfactants known as nonylphenol ethoxylates (NPEOs) that are frequently used for inhibiting corrosion and reducing surface tension during the hydraulic fracturing process. NPEOs can readily biodegrade under aerobic and anaerobic conditions, often accumulating as lower chain polymers and the monomer, nonylphenol. Furthermore, certain isomers of nonylphenol are environmentally recalcitrant, can be toxic to aquatic species, and act as reproductive toxins in humans. The fate of these compounds in subsurface systems is therefore of great interest to downgradient receptors who rely on aquifers for their water resources. Here, we investigate the degradation of NPEOs in a commercial additive as part of a complex fluid matrix by quantifying the rate, extent, and products of NPEO degradation in synthetic hydraulic fracturing fluids and a corrosion inhibitor additive. We demonstrate the accumulation of shorter-chain nonylphenol ethoxylates and daughter products in biologically active anaerobic sediment-groundwater microcosms, with a substantial portion sorbing to system sediments. Implications from this work include a better understanding of the fate of NPEOs and their intermediate breakdown products in subsurface sediments and groundwater, along with improved information on the degradability of NPEOs within hydraulic fracturing fluid formulations that could help guide industrial practice toward more benign surfactant alternatives.