BIOTRANSFORMATION OF NONYLPHENOL POLYETHOXYLATE SURFACTANTS BY ESTUARINE MIXED BACTERIAL CULTURES

Biotransformation of nonylphenol polyethoxylates (NPnEOs), a major cla ss of non-ionic surfactants, was studied under laboratory conditions b y using a static die-away method. The experiments were performed with autochthonous bacterial cultures that originated from two essentially different estuarine compartments, i.e., from the brackish water and sa line water layers of the highly stratified Krka River estuary, Croatia . Highly specific HPLC methods were applied to study biotransformation kinetics of individual NPnEO oligomers in the range of 1-16 EO units. Mixed bacterial cultures from the brackish water layer exhibited a si gnificantly greater ability to transform NPnEO than that from the sali ne water layer. The results suggest, however, that this difference sho uld not be interpreted as a salinity effect, but rather as a consequen ce of a better pre-adaptation of the brackish water bacteria to NPnEOs in their natural habitat. The biodegradation rates, calculated by pre suming first-order kinetics, showed a strong temperature dependence. T he estimated overall half-lives of NPnEOs under winter temperature con ditions (13 degrees C) ranged from 23-69 days, while the half-lives de termined under summer temperature conditions (22.5 degrees C) ranged f rom 2.5-35 days. Transformation kitnetics of larger, more hydrophilic, oligomers of NPnEOs was faster than that of the lower ones. In fact, the elimination of higher NPnEOs was followed by a significant formati on of the short-chain NPnEOs (nEO = 1-4). The main lipophilic intermed iate formed during the experiments was nonylphenol diethoxylate (NP2EO ), whose concentration in the medium increased by a factor of 10-20. I ts relatively fast accumulation was followed by a rather slow degradat ion. Consequently, residual concentrations of NP2EO were detected in t he medium even after 30 days.