Behavior of alkylphenol polyethoxylate metabolites during soil aquifer treatment

The attenuation of alkylphenol polyethoxylates (APEOs) metabolites was studied at a soil aquifer treatment (SAT) site located in Arizona, USA. Two parcels of water were monitored during infiltration; one parcel was predominantly oxic while the other was predominantly anoxic. In this study, only alkylphenol ethoxycarboxylates (APECs) and carboxyalkylphenol ethoxycarboxylates (CAPECs) were detected, no short-chained APEOs were observed—even under anoxic conditions. APEO metabolites were rapidly (<7 days) removed under both aerobic and anoxic conditions. In general, the length of the ethoxycarboxylate chain decreases with depth—at depths greater than 3 m, only alkylphenoxy acetic acids (AP1ECs), carboxyalkylphenoxy acetic acids (CAP1ECs), and alkylphenols (APs) remain. Under aerobic conditions, octylphenol and nonylphenol concentrations decreased by ~80% (w/w) within 3 m of the ground surface. Under anoxic conditions however, alkylphenol concentrations increased by ~200% during the first 1.5 m and then decreased during the next 1.5 m; overall, under anoxic conditions, alkylphenol concentrations increased by ~38% within 3 m. During infiltration, APEC and CAPEC concentrations decrease by more than 95% within 3 m of SAT. Alternate flooding and drying cycles appear to enhance overall APEO metabolite removal efficiencies.