Input and distribution of alkylphenol polyethoxylates in a stratified estuary

Abstract

The behaviour and fate of nonylphenol polyethoxylate surfactants (NPnEO) in the Krka River estuary were studied during 1990–1991. The study comprised determination of NPnEO input via municipal wastewaters and their subsequent distribution in the water column of the estuary. All quantitative determinations were performed by high-performance liquid chromatography using both normal-phase and reversed-phase systems. The concentrations of NPnEO in untreated municipal wastewaters varied in a wide range of 70 to 2960 μg/l. The oligomer distribution in all of the analysed wastewater samples was rather uniform characterised by a maximum at NP10EO which indicated heavy-duty detergents as the predominant source of NPnEO in the investigated area. Hydrophobic partitioning between dissolved and solid phase was found to play a significant role in wastewaters, as indicated by a relatively high percentage (6–60%) of NPnEO associated with wastewater suspended solids and by different oligomer distribution patterns in the two phases. The most important features of the NPnEO distribution in the estuary were: (1) exponential decrease of concentrations with increasing distance from sewage outlets, and (2) a rather complex vertical distribution pattern which reflected the basic hydrographic properties of this strongly stratified estuary. An efficient initial dilution was found to be the chief mechanism that was responsible for rather low NPnEO concentrations in estuarine waters. However, significant concentration differences were observed between the brackish water layer (1.1–6 μg/l) and saline water layers (0.1–0.7 μg/l). This suggested that the wastewater plume spreads into the estuary predominantly in the brackish water layer while the underlying saline water layer remains much less affected. However, NPnEO concentration maxima were observed at the two estuarine phase boundaries: air-brackish water (17 μg/l) and brackish water-saline water (9 μg/l). Relatively small changes of the oligomer distribution pattern in the water column, compared to that originally found in wastewaters, indicated that biodegradation played only a limited role as the mass balance determining process in the estuary.