Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids

Bioaccumulation: aquatic / sediment

Description of key information

BCF value: 0.893 - 6.32 L/kg (BCFBAF v3.01)

Additional information

Experimental bioaccumulation data are not available for Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids. The information gathered on environmental behaviour, 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 state that the substance is likely to show negligible bioaccumulation potential.

Environmental behaviour

Due to the high adsorption potential an effective removal of the substance in conventional sewage treatment plants (STPs) by sorption to biomass is likely. The low water solubility (1.5 - 5.1 mg/L), and high estimated log Kow (>6.74) and a log Koc > 5 indicate that the substance is highly lipophilic. If released into the aquatic environment, the substance will extensively adsorb to organic matter (e.g. sewage sludge in sewage treatment plants (STP)). Thus, the bioavailability in the water column and release via STP will be rapidly reduced.

Uptake/Absorption

If the substance is taken up by ingestion, absorption is expected to be low based on the molecular weight, size and structural complexity of the substance. For these large and complex structures a high degree of conformational flexibility is assumed. Dimitrov et al. (2002) revealed a tendency of decreasing log BCF in combination with an increase in conformational flexibility of molecules. The authors assume that this effect is related to an enhancement of the entropy factor on membrane permeability of chemicals. Thus, there is a high probability that the substance exists in a conformation which does not allow permeation. Furthermore, the some constituents of the substance have a high molecular weight 472.61 – 1011.45 g/mol. Thus, it is unlikely that it is readily absorbed, due to the sterical hindrance of crossing biological membranes. Following the ‘rule of 5’ (Lipinski et al., 2001), developed to identify drug candidates with poor oral absorption based on criteria regarding partitioning (log Kow > 5) and molecular weight (> 500 g/mol), the substance is considered to be poorly absorbed after oral uptake (also see Hsieh & Perkins, 1976).

This interaction between lipophilicity, bioavailability and membrane permeability is considered to be the main reason why the relationship between the bioaccumulation potential of a substance and its hydrophobicity is commonly described by a relatively steep Gaussian curve with the bioaccumulation peak approximately at log Kow of 6-7 (e.g., see Dimitrov et al., 2002; Nendza & Müller, 2007; Arnot and Gobas 2003). Substances with log Kow values above 10, which has been calculated for most of the components of the test substance, are considered to have a low bioaccumulation potential (e.g., Nendza & Müller, 2007 and 2010). Furthermore, for those substances with a log Kow value > 10 it is unlikely that they reach thepass level of being bioaccumulative according to ECHA Guidance R.11 (BCF > 2000; ECHA, 2017).

In addition QSAR calculations using BCFBAF v3.01 performed for Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids supported the assumption. BCF values ranged from 0.893 to 6.32 L/kg were obtained for the main constituents (Arnot-Gobas estimate, including biotransformation, upper trophic). Even though Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids is outside the applicability domain of the model, the estimation can be used as supporting indication of low bioaccumulation potential. 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, 2017).

Conclusion

Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids is characterized by a low water solubility (1.5 - 5.1 mg/L) and a high log Kow for most of its components. Based on the physico/chemical properties such as low water solubility and high potential for adsorption a reduced availability in water is expected. It can be concluded that the bioaccumulation potential of Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids is negligible. BCF/BAF values experimentally determined and estimated by QSAR (BCFBAF v3.01) also support this assumption (BCF values all well below 2000 L/kg).

Taking all these information into account, it can be concluded that bioaccumulation of Monopentaerythritol tetraesters and dipentaerythritol hexaesters of 2-ethylhexanoic and n-valeric acids is unlikely to occur.

A detailed reference list is provided in the CSR.