2-ethyl-2-(hydroxymethyl)-1,3-propanediyl dioleate

Bioaccumulation: aquatic / sediment

Description of key information

Taking all information into account bioaccummulation is assumed to be low.

Additional information

Experimental bioaccumulation data are not available for 2-ethyl-2-(hydroxymethyl)-1,3-propanediyl dioleate (CAS 25111-05-1). The high log Kow (> 10) as an intrinsic chemical 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 fate
Due to ready biodegradability and high potential of adsorption (log Koc ≥ 3.78), the substance can be effectively removed in conventional sewage treatment plants (STPs) by biodegradation and by sorption to biomass. The low water solubility (1.26 µg/L - 13.54 µg/L at 20 °C, pH=6.3 (OECD 105), mean: 7.40 µg/L) and high estimated log Kow indicate that the substance is highly lipophilic. If released into the aquatic environment, the substance undergoes extensive biodegradation and sorption on organic matter. Thus, the bioavailability in the water column is reduced rapidly. The relevant route of uptake of the substance in aquatic organisms is expected to be predominantly by ingestion of particle bound substance. 

Metabolism of enzymatic hydrolysis products
In general, after oral ingestion, aliphatic esters of polyhydroxy alcohols (Polyol) and fatty acids are expected to undergo chemical changes in the gastro-intestinal fluids as a result of enzymatic hydrolysis. Thus, 2-Ethyl-2-(hydroxymethyl)-1,3-propanediyl dioleate is assumed to release trimethylolpropane (TMP, parental polyol) and the fatty acid moieties, even if hydrolysis is not assumed to be rapid for polyol esters with more than 3 ester groups. Moreover, pentaerythriol- and dipentaerythritol-esters are expected to be slowly hydrolysed based on in vitro studies, in which the hydrolysis rate of the polyol ester Pentaerythritol tetraoleate was very slow compared to the hydrolysis rate of the triglyceride Glycerol trioleate (Mattson and Volpenhein, 1972). Thus, since it is assumed that esters of polyols (pentaerythritol, dipentaerythritol and trimethylolpropane) have the same metabolic fate, TMP Polyol esters are expected to be hydrolysed slowly as well.

The log Kow of the first cleavage product trimethylolpropane is -0.47 and it is highly soluble in water (>100 g/L) (OECD SIDS, 2013). Consequently, there is no potential for trimethylolpropane to accumulate in adipose tissue. The other cleavage products, the fatty acids, can be stored as triglycerides in adipose tissue depots or be incorporated into cell membranes. At the same time, fatty acids are also required as a source of energy. Thus, stored fatty acids underlie a continuous turnover as they are permanently metabolized and excreted. Bioaccumulation of fatty acids only takes place, if their intake exceeds the caloric requirements of the organism.the fatty acids are stepwise degraded by beta-oxidation based on enzymatic removal of C2 units in the matrix of the mitochondria in most vertebrate tissues. The C2 units are cleaved as acetyl-CoA, the entry molecule for the citric acid cycle. For the complete catabolism of unsaturated fatty acids such as oleic acid, an additional isomerization reaction step is required. The omega- and alpha-oxidation, alternative pathways for oxidation, can be found in the liver and the brain, respectively (CIR, 1987).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). Saturated fatty acids (SFA; C12 - C24) as well as mono-unsaturated (MUFA; C14 - C24) and poly-unsaturated fatty acids (PUFA; C18 - C22) were naturally found in muscle tissue of the rainbow trout (Danabas, 2011) and in the liver (SFA: C14 - C20; MUFA: C16 - C20; PUFA: C18 - C22) of the rainbow trout (Dernekbasi, 2012).The remaining cleavage product trimethylolpropane is easily absorbed and can either remain unchanged or may further be metabolized or conjugated (e.g. glucuronides, sulfates, etc.) (OECD SIDS, 2013)

Data from QSAR calculation
Additional information on bioaccumulation could be gathered through BCF/BAF calculations using BCFBAF v3.01. The estimated BCF values for 2-ethyl-2-(hydroxymethyl)-1,3-propanediyl dioleate indicate negligible bioaccumulation in organisms. When including biotransformation, BCF and BAF values of 0.893 - 18.94 and 0.893 - 30 L/kg, respectively were obtained (Arnot-Gobas estimate, including biotransformation, upper trophic). The results with the monoester component of the UVCB substance are within the training set of the model and thus fully reliable (BCF: 18.94 L/kg; BAF: 30 L/kg). Taking these values into account the substance has a low potential for bioaccumulation. The (Q)SAR calculations with the di- and triester which were not in the applicability domain of the model resulted in lower BCF/BAF values. This supports the tendency that substances with high log Kow values (> 10) 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, 2014).

Conclusion
The biochemical process metabolizing aliphatic esters is ubiquitous in the animal kingdom. Based on the enzymatic hydrolysis of aliphatic esters and the subsequent metabolism of the corresponding carboxylic acid and alcohol, it can be concluded that the high log Kow, which indicates a potential for bioaccumulation, overestimates the true bioaccumulation potential of 2-ethyl-2-(hydroxymethyl)-1,3-propanediyl dioleate since it does not reflect the metabolism of substances in living organisms. BCF/BAF values estimated with the BCFBAF v3.01 program also indicate that isooctadecyl isooctadecanoate 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 2-ethyl-2-(hydroxymethyl)-1,3-propanediyl dioleate is low.