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EC number: 292-947-3 | CAS number: 91031-45-7
Bioaccumulation: aquatic / sediment
Administrative data
Link to relevant study record(s)
Description of key information
By taking into account all relevant data for the assessment of the bioaccumulation potential, it can be concluded that fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) has a low potential for bioaccumulation and biomagnification through the food chain.
Key value for chemical safety assessment
Additional information
Aquatic bioaccumulation
Experimental bioaccumulation data are not available for fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) (CAS 91031-45-7). The high log Kow (5.73 -15.57) as an intrinsic property of the substance indicates a potential for bioaccumulation. However, the information gathered on environmental behaviour and metabolism, in combination with QSAR-estimated values, provide enough evidence (in accordance to the Regulation (EC) No 1907/2006, Annex XI General rules for adaptation of the standard testing regime set out in Annexes VII to X, 1.2), to cover the data requirements of Regulation (EC) No 1907/2006, Annex IX to state that the substance is likely to show negligible bioaccumulation potential.
Environmental behavior
The low water solubility (< 0.05 mg/L) and high estimated log Kow indicate that for fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) is highly lipophilic. Due to ready biodegradability and potential for adsorption (log Koc > 3), the substance can be effectively removed in conventional STPs either by biodegradation or by sorption to biomass. However, if released in the aquatic environment, the substance undergoes extensive biodegradation and sorption on organic matter, as well as sedimentation. Thus, the bioavailability of the substance in the water column is reduced rapidly. The relevant route of uptake of for fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) in organisms is considered predominately by ingestion of particle bounded substance.
Metabolism of aliphatic esters
Should the substance be taken up by fish during the process of digestion and absorption in the intestinal tissue, aliphatic esters like fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) is expected to be initially metabolized via enzymatic hydrolysis in the corresponding free fatty acids (C16 and C18) and triethylene glycol. The hydrolysis is catalyzed by classes of enzymes known as carboxylesterases or esterases (Heymann, 1980). The most important of which are the B-esterases in the hepatocytes of mammals (Heymann, 1980; Anders, 1989). Carboxylesterase activity has been noted in a wide variety of tissues in invertebrates as well as in fish (Leinweber, 1987; Suldano et al, 1992; Barron et al., 1999, Wheelock et al., 2008). The catalytic activity of this enzyme family leads to a rapid biotransformation/metabolism of xenobiotics which reduces the bioaccumulation or bioconcentration potential (Lech & Bend, 1980). It is known for esters that they are readily susceptible to metabolism in fish (Barron et al., 1999) and literature data have clearly shown that esters do not readily bioaccumulate in fish (Rodger & Stalling, 1972; Murphy & Lutenske, 1990; Barron et al., 1990). In fish species, this might be caused by the wide CaE distribution, high tissue content, rapid substrate turnover and limited substrate specificity (Lech & Melancon, 1980; Heymann, 1980).
Metabolism of enzymatic hydrolysis products
Corresponding alcohol
Triethylene glycol is the corresponding alcohol metabolite from the enzymatic reaction of fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO). The metabolite is characterized by a low log Kow of -1.75, indicating a low potential for bioaccumulation (Meylan & Howard, 1995). Moreover, triethylene glycol is of generally low toxicity to aquatic organisms (OECD, 2004).
Corresponding fatty acids
Lipids and their key constituent fatty acids are, along with protein, the major organic constitute of fish and they play a major role as sources of metabolic energy in fish for growth, reproduction and movement, including migration (Tocher, 2003). In fishes, the fatty acids metabolism in cell covers the two processes anabolism and catabolism. The anabolism of fatty acids occurs in the cytosol, where fatty acids esterified into cellular lipids that is the most important storage form of fatty acids. The catabolism of fatty acids occurs in the cellular organelles, mitochondria and peroxisomes via a completely different set of enzymes. The process is termed ß-oxidation and involves the sequential cleavage of two-carbon units, released as acetyl-CoA through a cyclic series of reaction catalyzed by several distinct enzyme activities rather than a multienzyme complex (Tocher, 2003). As fatty acids are naturally stored in fat tissue and re-mobilized for energy production is can be concluded that even if they bioaccumulate, bioaccumulation will not pose a risk to living organisms. Fatty acids (typically C14 to C24 chain lengths) are also a major component of biological membranes as part of the phospholipid bilayer and therefore part of an essential biological component for the integrity of cells in every living organism (Stryer, 1994).
Data from QSAR calculation
Additional information about this endpoint could be gathered through BCF/BAF calculation using BCFBAF v3.01 (Müller, 2011). The estimated BCF/BAF values indicate a low bioaccumulation in organisms (BCF: 51.46 - 51.86 L/kg (monoester); 0.89 L/kg (diester), BAF: 51.49 - 52.66 L/kg (monoester); 0.90 - 0.92 (diester), Arnot-Gobas estimate, including biotransformation, upper trophic).
Even though the diester component of fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) is outside the applicability domain of the model the results can be used as supporting indication that the potential of bioaccumulation is low. The model training set is only consisting of substances with log Kow values of 0.31 - 8.70. But it supports the tendency that substances with high log Kow values have a lower potential for bioconcentration as summarized in the ECHA Guidance R.11 and they are not expected to meet the B/vB criterion (ECHA, 2008).
Conclusion
Aliphatic esters are biotransformed to fatty acids and the corresponding alcohol component by the ubiquitous carboxylesterase enzymes in aquatic species. Based on the rapid metabolism it can be concluded that the high log Kow, which indicates a potential for bioaccumulation, overestimates the bioaccumulation potential of fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO). BCF/BAF values estimated with the BCFBAF v3.01 program also indicate that the substance will not be bioaccumulative (all well below 2000 L/kg). Taking all these information into account, it can be concluded that the bioaccumulation potential of fatty acids, C16-18, 1,2-ethanediylbis(oxy-2,1-ethanediyl) esters (3EO) is low.
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