Fate and distribution of the octyl- and nonylphenol ethoxylates and some carboxylated transformation products in the Back River, Maryland

The concentrations of nonylphenol (NP), octylphenol (OP), their ethoxylates (NP1-16EO and OP1-5EO respectively) and some of their carboxylated derivatives (NP1-2EC and OP1EC quantitatively; NP3-4EC and OP2EC qualitatively) were measured in water samples from the Back River, MD, a sub-estuary of the Chesapeake Bay that receives effluent from a large municipal wastewater treatment plant. The most abundant of the alkylphenolic compounds (APEs) were the carboxylates (APECs, >95% of the APE-related compounds), followed by NP in September and October, and NP1-2EO in March. Ratios of the different compounds' concentrations provide evidence for the season dependency of two different degradation pathways. NP concentrations found in this study, 0.087-0.69 mu g L(-1), were below acute toxicity thresholds, and below US EPA water quality criteria; although in March, concentrations were close to 40% of the chronic exposure limit for saltwater, 1.7 mu g L(-1). A simple steady-state model of the Back River suggested that total NPE concentrations in the estuary varied in accordance with concentrations in the wastewater treatment plant effluent, especially in the case of the APECs. This model also suggested that in the fall sampling events, when rain occurred, APEOs present in particulate matter might have originated in the river's tributaries rather than the treatment plant.