Alkylphenol Polyethoxylate Metabolite Behavior During Short-Term Soil Aquifer Treatment

The attenuation of alkylphenol polyethoxylate (APEO) metabolites was studied at a soil aquifer treatment (SAT) facility located in Mesa, Arizona, USA. SAT is a technique commonly used in arid environments to augment groundwater supplies. In SAT, municipal wastewater is discharged into basins and allowed to infiltrate into the subsurface; the basins are most often filled for several days and then allowed to dry out. During SAT the quality of the recharged water is substantially improved. Because this water may eventually be used to augment drinking water supplies, there is a concern whether organic contaminants survive SAT. APEO metabolites are among the most frequently detected anthropogenic contaminants in the environment. The ubiquitous presence of these compounds may be of concern because they are relatively recalcitrant, can sorb and accumulate in soils and sediments, can bioaccumulate in plants and animals, and can be estrogenic to wildlife at low concentrations. In this study, two parcels of water were monitored during SAT -- one aerobic, the other anaerobic. During infiltration, under aerobic and anaerobic conditions, both alkylphenol ethoxycarboxylates (APECs) and carboxyalkylphenol ethoxycarboxylates (CAPECs) were substantially attenuated (> 90%) within 3 m. As expected, nonylphenol was removed under aerobic conditions, but produced under anaerobic conditions. Interestingly, no short-chained APEOs were detected. The rapid attenuation of CAPECs was surprising, as other researchers have found these metabolites to be very persistent. During infiltration, APEO metabolites with the longest ethoxycarboxylate side chain are attenuated fastest. Unlike several recent studies, alkylphenoxyacetic acids (AP1ECs) and carboxyalkylphenoxyacetic acids (CAP1ECs) were almost twice as abundant as alkylphenoxyethoxyacetic acids (AP2ECs) and carboxyalkylphenoxyethoxyacetic acids (CAP2ECs). Nonylphenol concentrations in both the wastewater and effluent SAT water were > 10 μg/L; these concentrations are high enough to induce estrogenic responses in certain animals. The ability of the SAT system to remove APEO metabolites decreased over time; this was indicated by the accumulation of NP and breakthrough of longer ethoxy chain metabolites at 1.5 m and 3 m during the study period. These observations suggest that the drying cycle is necessary to maintain high APEO metabolite attenuation efficiencies in SAT systems. Overall, short-term SAT appears to be very effective at eliminating APEO metabolites.