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Fate modeling of nonylphenol ethoxylates and their metabolites in the Dutch Scheldt and Rhine estuaries: validation with new field data
Jonkers, N.; Laane, R.W.P.M.; de Graaf, C.; de Voogt, P. (2005). Fate modeling of nonylphenol ethoxylates and their metabolites in the Dutch Scheldt and Rhine estuaries: validation with new field data. Est., Coast. and Shelf Sci. 62: 141-160. dx.doi.org/10.1016/j.ecss.2004.08.014
In: Estuarine, Coastal and Shelf Science. Academic Press: London; New York. ISSN 0272-7714, more
Peer reviewed article  

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Authors  Top 
  • Jonkers, N.
  • Laane, R.W.P.M., more
  • de Graaf, C.
  • de Voogt, P., more

Abstract
    The environmental behavior of nonylphenol ethoxylates (A9PEO) in the Rhine and Scheldt estuaries (The Netherlands) was investigated using a hydrodynamic advection-dispersion fate model (ECoS 3). The model was validated with the results of field studies, in which A9PEO as well as the metabolites nonylphenoxy ethoxy acetic acids (A9PEC) and nonylphenol (NP) were analyzed in sediment, water and suspended particulate material (SPM) samples using LC-MS methods. Maximum actual concentrations observed in surface sediments were 620, 560 and 1100 ng g−1 d.w. for A9PEO, A9PEC and NP, respectively. In the dissolved phase, maximum observed concentrations amounted to 1100 ng L−1 (A9PEO), 6500 ng L−1 (A9PEC) and 960 ng L−1 (NP). Clear spatial trends were observed for dissolved A9PEO and metabolites in the Scheldt estuary, with decreasing concentrations going downstream. This concentration decrease was steeper than for conservatively behaving compounds. This trend was not visible in the Rhine estuary. The fate model was applied to A9PEO and metabolites in both estuaries. Transport of chemicals in the water column was considered as a longitudinal one-dimensional process through a number of estuary segments. For the Rhine estuary, to cope with the stratification observed, a model structure was chosen consisting of two water layers above each other, between which exchange was possible. Sedimentation/erosion processes were included in the model. A biodegradation scheme was incorporated, and rates were adjusted to fit the calculated concentration profiles with the actual profiles of both A9PEO and its metabolites. In this way, field biodegradation rates for A9PEO, A9PEC and NP could be derived, which were in agreement with values from literature. The measured dissolved concentration profiles as well as salinity and concentrations of SPM could be described successfully by the model. The concentrations calculated in SPM and sediment were of the same order of magnitude as the actual concentrations. In the Rhine estuary, additional sources of A9PEO had to be included to account for the relatively high concentrations in the middle of the estuary. The fate model for the Scheldt estuary could be slightly improved by using salinity-dependent biodegradation rates. A sensitivity analysis of the model showed that in the Scheldt estuary, the environmental process with the strongest influence on the dissolved concentration profiles of A9PEO and metabolites is biodegradation. In the Rhine estuary, the water residence time is too short for significant biodegradation to occur, and in this estuary the dissolved concentration profiles were mainly influenced by the additional A9PEO sources.

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