The fate and behavior of octyl- and nonylphenol ethoxylates and their derivatives in three American wastewater treatment plants and the Back River, Maryland

Abstract

The octyl- and nonylphenol ethoxylates (collectively known as alkylphenol ethoxylates, APEOs) are a family of widely used surfactants in industrial processes and as detergents in both industrial and household applications. After being used, the APEOs are transformed into more toxic and endocrine disrupting products, such as short-chain APEOs, nonylphenol (NP), and octylphenol (OP). The main objective of the present work was to study the fate of the APEOs and transformation products (APEs) in three American wastewater treatment plants (WWTPs) and in Back River, an estuary of the Chesapeake Bay that receives treated effluent from one of the plants. In order to accomplish this, analytical methods were developed based on solid-phase extraction for water, accelerated solvent extraction for solids, and isotope dilution liquid chromatography/tandem mass spectrometry for quantitation. Analysis in the WWTPs showed that influent wastewater had similar APEs concentrations, whereas effluent concentrations were only similar when samples from the same season (fall or winter) were compared, with concentrations being several times higher in winter than in fall. Sorption to particulate was approximately 1.6 times higher for nonylphenolic compounds than for their octylphenolic counterparts, in agreement with their difference in Kow values. Effluent concentrations and APEO removal rates--the latter averaging 99% in summer and 94% in winter for the NPEOs--were strongly correlated to water temperature, and no correlation was found with suspended solids or organic carbon removal. In Back River the most abundant of the APEs were the carboxylated transformation products (APECs, > 95% on mass basis), followed by NP in September and October, and NP1-2EO in March. NP concentrations found, 0.087 - 0.69 μg/L, were below acute toxicity thresholds, and generally below recently proposed water quality criteria by the US EPA. Total NPE concentrations in the Back River seemed to vary in accordance to the concentrations in the WWTP effluent, especially in the case of the APECs. However, a closer analysis of the data suggested that in the fall sampling events, when rain occurred, the ethoxylates present in the particulate matter originated in the river's tributaries rather than the WWTP.