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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The potential for bioaccumulation of Tetraesters of pentaerythritol with 2-ethylhexanoic acid, heptanoic acid and nonanoic acid (EC 806-879-4) is assumed to be low based on all available data. 

Key value for chemical safety assessment

Additional information

Experimental bioaccumulation data are not available for Tetraesters of pentaerythritol with 2-ethylhexanoic acid, heptanoic acid and nonanoic acid (EC 806-879-4). 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 behaviour

Due to ready biodegradability and high potential of adsorption, the substance can be effectively removed in conventional sewage treatment plants (STPs) by biodegradation and by sorption to biomass. The low water solubility (< 0.15 mg/L at 20 °C) 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 aliphatic esters

Should the substance be taken up by fish during the process of digestion and absorption in the intestinal tissue, aliphatic esters like Tetraesters of pentaerythritol with 2-ethylhexanoic acid, heptanoic acid and nonanoic acid (EC 806-879-4) are expected to be initially metabolized via enzymatic hydrolysis to the corresponding free fatty acid (here: 2-ethylhexanoic acid, C7, C9) and the free fatty alcohols (here: pentaerythritol). The hydrolysis is catalysed 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; Soldano 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 distribution of carboxylesterase, high tissue content, rapid substrate turnover and limited substrate specificity (Lech & Melancon, 1980; Heymann, 1980). The metabolism of the enzymatic hydrolysis products is presented in the following chapter.

 

Metabolism of enzymatic hydrolysis products

The metabolism of fatty acids in mammals is well known and has been investigated intensively in the past (Stryer, 1994). The free fatty acids can either be stored as triglycerides or oxidized via mitochondrial ß-oxidation removing C2-units to provide energy in the form of ATP (Masoro, 1977). Acetyl-CoA, the product of the ß-oxidation, can further be oxidized in the tricarboxylic acid cycle to produce energy in the form of ATP. As fatty acids are naturally stored as triglycerides in fat tissue and re-mobilized for energy production it 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). 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).

For pentaerythritol, the hydroxyl groups make the substance a candidate for metabolism or conjugation with e.g. glutathione and subsequent excretion.

 

Data from QSAR calculation

Additional information on bioaccumulation could be gathered by (Q)SAR calculations. Two different models were applied, the BCF read across model which is part of EPISuite v4.11.
The estimated BCF values for the substance indicate negligible bioaccumulation in organisms. BCF and BAF values of 0.893 - 0.894 L/kg, respectively were obtained (BCFBAF v3.01, Arnot-Gobas estimate, including biotransformation, upper trophic). Even though the substance is outside the applicability domain of the model the (Q)SAR calculations 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 (> 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 the substance 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 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 the substance is low.

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within the CSR.

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