Registration Dossier

Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

BCF = 3-71 L/kg (BCFBAF v3.01, regression based estimate)
BCF/BAF = 0.9/0.9 (BCFBAF v3.01, Arnot-Gobas, upper trophic)

Key value for chemical safety assessment

Additional information

No experimental data evaluating the bioaccumulation potential of Fatty acids, C14-18 and C16-18-unsatd., mixed esters with castor oil, castor oil fatty acids, 2-ethylhexanoic acid and 2,2-bis(hydroxymethyl)-1-butanol (CAS No. 92113-48-9) is available. Therefore, all available related data is combined in a Weight of Evidence (WoE) approach, which is in accordance to the REACh 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. 1907/2007 Annex IX (ECHA, 2012c).

Environmental behaviour

Fatty acids, C14-18 and C16-18-unsatd., mixed esters with castor oil, castor oil fatty acids, 2-ethylhexanoic acid and 2,2-bis(hydroxymethyl)-1-butanol (CAS No. 92113-48-9) is a substance of unknown, variable composition or biological origin (UVCB), consisting of main components with estimated high partition coefficients (calculated log Kow = 10). In addition, the calculated log Koc values above 5 indicate that the main components of this UVCB will adsorb to suspended organic particles, dissolved organic matter (DOM) and to some degree biota in the aquatic environment (e.g., see Jaffé, 1991). The substance is considered to be readily biodegradable indicating that the substance will neither be persistent in the aquatic nor the terrestrial compartment. Hence the concentration of this substance in the aquatic environment is expected to be low as it will be in general effectively removed in conventional STPs either by biodegradation or by sorption to biomass. Considering this one can assume that the availability of Fatty acids, C14-18 and C16-18-unsatd., mixed esters with castor oil, castor oil fatty acids, 2-ethylhexanoic acid and 2,2-bis(hydroxymethyl)-1-butanol (CAS No. 92113-48-9) in the aquatic environment is generally low, which reduces the probability of adsorption and uptake from the surrounding medium into organisms (e.g., see Björk, 1995, Haitzer et al., 1998).

If environmental concentrations facilitate exposure, the uptake of the substance from medium into organisms is expected to be low based on the molecular weight, size and structural complexity. The main components feature high molecular weights of 513 to 976 g/mol. Even if dermal adsorption of substance cannot per se be excluded, it is conducive to say that with such molecular weights they may not be readily taken up due to the steric hindrance of crossing biological membranes.

This interaction between hydrophobicity, bioavailability and membrane permeability is considered to be the main reasons why the relationship between the bioaccumulation potential of a substance and its hydrophobicity is commonly found to be 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; Arno and Gobas 2003). Substances with log Kow values above 10, which have been calculated all main components of this substance, are, however, again considered to have a low bioaccumulation potential (e.g. see Nendza & Müller, 2007; 2010). Furthermore, for those substances with a log Kow value >10 it is recognized by the relevant authorities that it is unlikely that they accomplish the pass level of being bioaccumulative according to OECD criteria for the PBT assessment (log BCF = 2000; ECHA, 2011). This assumption is supported by QSAR calculations using BCFBAF v3.01 performed for the main components (Gerloff-Elias, 2013). BCF values were calculated to be between 3 and 71 L/kg (regression based method). A model which considered biotransformation calculated even lower BCF and BAF values of 0.90 L/kg, respectively (Arnot-Gobas, upper trophic). Even though the constituents of this substance are, due to their high calculated log Kow values, in most cases outside the applicability domain of the used model (model training set is constituted of substances with log Kow values in the range of 0.31 to 8.70), the calculations (especially the low BCF values calculated using the Arnot-Gobas method) reflect the biotransformation assumed for this substance.

Metabolism of aliphatic esters and metabolites

The log Pow of > 10 suggests that the components of this UVCB are favourable for absorption by micellar solubilisation, as this mechanism is of importance for highly lipophilic substances (log Pow > 4), which are poorly soluble in water (< 1 mg/L). After uptake by organisms, biotransformation of the substance by carboxylesterases into 2-Ethylhexanoic acid, C14-C20 fatty acids and the corresponding alcohol (i.e. trimethylpropane) is expected. However, the molecular weight range of > 513 g/mol and the high octanol/water partition coefficient of > 10 in combination with the low water solubility, indicates a low absorption and correspondently slower hydrolysis rate for this substance. All three metabolites are not of concern for the environment. A REACh registration dossier of 2-Ethylhexanoic acid is available and can be publicly viewed on the ECHA webpage (http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances).

All metabolites exhibit no potential for bioaccumulation (for further information see chapter 7.1 of the technical dossier).

Conclusion

Hence, the main components of Fatty acids, C14-18 and C16-18-unsatd., mixed esters with castor oil, castor oil fatty acids, 2-ethylhexanoic acid and 2,2-bis(hydroxymethyl)-1-butanol (CAS No. 92113-48-9) are biotransformed to fatty acids and the corresponding alcohol components by the ubiquitous carboxylesterase enzymes in aquatic species. Based on the metabolism it can be concluded that the high log Kow, which indicates a potential for bioaccumulation, overestimates the true bioaccumulation potential of this substance. In addition calculated BCF/BAF values clearly indicate a neglible potential for bioaccumulation. Taking all these information into account, it can be considered that bioaccumulation of Fatty acids, C14-18 and C16-18-unsatd., mixed esters with castor oil, castor oil fatty acids, 2-ethylhexanoic acid and 2,2-bis(hydroxymethyl)-1-butanol (CAS No. 92113-48-9) is unlikely to occur.

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