engleski

Biotransformation of nonylphenol polyethoxylate surfactants by estuarine mixed bacterial cultures

Biotransformation of nonyphenol polyethoxylates (NPnEO), a major class of non-ionic surfactants, was studied under laboratory conditions by using a static die-away method. The experiments were performed with various autochthonous bacterial cultures that originated from two essentially different estuarine compartments, i.e. from the brackish water and saline water layers, of the highly stratified Krka River estuary. Highly specific HPLC methods were applied to study biotransformation kinetics of individual NPnEO oligomers in the range of 1-16 EO units. Mixed bacterial culture from the brackish water layer exhibited a significantly greater ability to transform NPnEO than that from the saline water layer. The results suggest, however, that this difference should not be interpreted as a salinity effect, but rather as a consequence of a better pre-adaptation of the brackish water bacteria to investigated pollutants in their natural habitat. The biodegradation rates, calculated by presuming first-order kinetics, have shown a strong temperature dependence. The estimated overall half-life of NPnEO under winter temperature conditions (13 °C) exceeded 1 month for both mixed bacterial cultures, whilst the half-lives of NPnEO determined under summer temperature conditions (22.5 °C) ranged from 2.5-14 days. It was observed that transformation kinetics of higher, more hydrophilic, oligomers of NPnEO was faster than that of the lower ones. In fact, the elimination of higher NPnEO was followed by a significant formation of the short-chain NPnEO (nEO=1-4). The main lipophilic intermediate formed during the experiments was nonylphenol diethoxylate (NP2EO) whose concentration in the medium increased by a factor of 25. Its relatively fast accumulation was followed by a rather slow degradation. Consequently, residual concentrations of NP2EO were detected in the medium even after 30 days.

biotransformation ; nonionic surfactants ; estuaries

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