Fate of Alkylbenzenesulfonates and Dialkyltetralinsulfonates in Sewage-Contaminated Groundwater

Abstract

The fate and transport of linear alkylbenzenesulfonates (LAS) during sewage treatment, infiltration, and ground-water transport were investigated at the U.S. Geological Survey Cape Cod Toxic Waste Research Site (CCTWRS). High-performance liquid chromatography with fluorescence detection (HPLC/FL) and fast atom bombardment mass spectrometry (FAB/MS) were used for this investigation. HPLC/FL results indicated 96% removal of LAS from the aqueous phase during sewage treatment and an additional 3% during infiltration to give groundwater concentrations of LAS <10-20 µg/L. Removal refers to parent compound disappearance due to processes such as partitioning, primary biodegradation to intermediates, or mineralization. Treatment and infiltration have affected preferential removal of long alkyl chain LAS homologues. LAS disappearance during groundwater infiltration can be described by first-order kinetics. FAB/MS confirmed trace levels of LAS in groundwater 20-500 m downgradient from infiltration. Trace levels of LAS detected in groundwater at 500 m from infiltration have been stable over a period of time corresponding to between 50 and 500 LAS half-lives. Dialkyltetralinsulfonates (DATS), reaction byproducts of LAS synthesis, were identified by FAB/MS and estimated to be at concentrations comparable to LAS in groundwater. LAS and DATS represented approximately 5% of the methylene blue active substance (MBAS) response measured in groundwater within 500 m of infiltration. Branched-chain alkylbenzenesulfonates (ABS) were observed in wells 3000 and 3400 m downgradient from infiltration beds. An ABS concentration of 2.1 mg/L was measured in groundwater from the 2900-m-downgradient well, accounting for 90% of MBAS and 50% of dissolved organic carbon (DOC) concentrations.