Fate of nonylphenol ethoxylates and their metabolites in two Dutch estuaries: Evidence of biodegradation in the field

The environmental behavior of nonylphenol ethoxylates (A(9)PEO) and their metabolites was investigated in field studies in the two Dutch estuaries Western Scheldt and the Rhine estuary. Using liquid chromatography-electrospray mass spectrometry (LC-ES-MS) analysis after solid phase extraction, A(9)PEO, nonylphenol (NP), and the carboxylated metabolites (A(9)PEC) were determined in surface water and sediments. Maximum dissolved concentrations of 2.3, 0.9, and 8.1 mug L-1, respectively, were found. In sediments, maximum concentrations of 242 and 1080 ng g(-1) for A9PEO and NP were observed. In almost half of the sediment samples, concentrations of A(9)PEC in sediments were below the detection limit. Occasionally relatively high values were observed, with a maximum of 239 ng g(-1). Metabolites of the carboxy alkylphenoxy ethoxy acetic acids (CAPEC) type could not be detected in any of the sediment or water samples. In the Scheldt estuary, dissolved concentration profiles showed nonconservative behavior for all detected compound groups. While A(9)PEO and NP concentrations strongly decreased along the salinity gradient, this decrease was weaker for the A9PEC metabolites. The increasing concentration ratio of A(9)PEC/A(9)PEO clearly illustrates the important role that aerobic biodegradation plays in the estuarine fate of these compounds. It is concluded that the oxidative hydrolytic degradation pathway is the main degradation route in this nonstratified estuary. At high salinities, where concentrations drop to background levels of around 50 ng L-1, this ratio decreases to about unity. Simple model calculations show that this can be explained if continuous diffuse discharges (e.g. from the intensive shipping in the estuary) are assumed. For the stratified Rhine estuary the water concentration profiles are less pronounced, possibly due to more complicated and turbulent water flows and point sources from the Rotterdam harbors.