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Environmental fate & pathways

Endpoint summary

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Description of key information

Experimentally determined BCF-values given for pure homologues and summarized in the publication of Tolls et al. (2000) are used to address the endpoint bioaccumulation in water. It can be stated that bioaccumulation of alcohol ethoxylates is regarded to be negligible as the surfactants will be rapidly metabolised.

Additional information

In a publication on the bioconcentration of alkylethoxylates Tolls et al. (2000) reported BCF-values ranging from <5 to 387.5 whereas uptake rates varied from 330 to 1660 (L x kg/d) and elimination rates varied from 3.3 to 59 per day. The authors concluded that the high values of elimination rate constants suggest that the tested fathead minnow efficiently biotransform alcohol ethoxylates, thereby preventing them from attaining high concentrations in fish.

In a further publication of Dyer et al. (2008) biotransformation of two surfactants: C12-2-LAS and C13EO8 were tested in subcellular and cellular hepatic systems. The subcellular systems tested were liver homogenates and microsoms from the common carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss). Cellular systems consisted of primary hepatocytes from the common carp (Cyprinus carpio) and PLHC-1 cells, hepatocarcinoma cells from the desert topminnow (Poeciliopsis lucida). All in vitro systems were exposed to radiolabeled test compounds and assayed for biotransformation using liquid scintillation and thin layer chromatographic methods. Predicted BCF-values corresponded closely to measured values in several fish species, verifying the utility of in vitro systems in refining Kow-only-based BCFs via the inclusion of biotransformation rates.

Resulting from that study biotransformation of C13EO8 could be demonstrated with both, primary hepatocytes and PLHC-1 cells, although with different metabolic profiles. First-order in vitro clearance rates based on exposure of C13EO to rainbow trout and carp microsomes and primary hepatocytes from carp lead to predicted BCF-values which were below 98 for all test systems.

In a recent publication of Munoz (2010), in vivo experiments were described which were carried out with pure homologues of linear alcohol ethoxylates. The authors studied the uptake and elimination kinetics, bioconcentration (BCF), biotransformation (identification of the metabolites generated by an organism), and depuration at different exposure levels. Steady state BCF-values ranged from 99.4 to 130 L/kg/d for the tested alcohol ethoxylates. For C12EO6 the rate of uptake (k1) ranged from 63.2 to 122.6 L/kg/d. The rate of uptake was not affected by the exposure concentration. For the rate of elimination (k2) the results showed a very slight decrease with increasing exposure level. As internal degradation products in fish, the glucuronic conjugate of alcohol ethoxylates was detected. The results suggest that predominant biotransformation process for alcohol ethoxylates is a phase II biotransformation. Although the depuration percentage was very high at the beginning of the elimination phase, a slight increase was observed over time. Alcohol ethoxylates were considered to have a delayed elimination and potential of short term bioaccumulation according to Beek (2000).

 

The common principle of the biotransformation of surfactants is either an enzymatic cleavage of the two surfactant molecule moieties (forming a fatty alcohol/acid and a hydrophilic product) or is a terminal oxidation and subsequent stepwise degradation of the alkyl chain (leaving again a hydrophilic product). The metabolism of the surfactant alkyl chain through a combination of omega- and beta-oxidations with subsequent excretion of a short chain derivative has been demonstrated for several fish species (Newsome et al., 1995; Van Egmond et al.,1999).

 

In conclusion, bioconcentration factors of alcohol ethoxylates in the aqueous phase are generally below the level of concern, and for some nonionic surfactants can be quantitatively related to the length of the hydrophobic and hydrophilic components. There is also evidence that overall molecular size may place constraints on biological uptake. The various studies cited raise no concerns with respect to long-term retention of accumulated surfactant material in tissue, and indeed they present considerable evidence that alcohol ethoxylates are rapidly eliminated and metabolised. Although the fate of metabolites of AE has not been thoroughly studied, rapid biodegradation of alcohol ethoxylates in the aquatic environment is considered to be a mitigating aspect, since the rate of biodegradation of alcohol ethoxylates are significantly faster than the uptake rates of bioaccumulation.

 

 

References:

Dyer, S. D., Bernhard, M. J., Cowan-Ellsberry, C. C., Perdu-Durand, E., Demmerle, S. and Cravedi, J.-P. (2008):In vitro biotransformation of surfactants in fish. Linear alkylbenzene sulfonate (C12 -LAS) and alcohol ethoxylate (C13EO8). Chemosphere 72, 850 -862.

Munoz DA, Gomez-Parra A and Gonzalez-Mazo E (2010):Influence of the molecular structure and exposure concentration on the uptake and elimination kinetics, bioconcentration, and biotransformation of anionic and nonionic surfactants.

Environ. Toxicol. Chem, 29 (8): 1721-1734

Newsome, C. S., Howes, D., Marshall, S. J. and Van Egmond, R. A. (1995): Fate of some anionic and alcohol ethoxylate surfactants inCarassius auratus. Tenside Surfact. Deter. 32, 498 -503.

Van Egmond, R., Hambling, S. and, S. (1999): Bioconcentration, biotransformation, and chronic toxicity of sodium laurate to zebrafish (Danio rerio).