Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Based on the intrisic properties, fate, metabolism and QSAR data, there is strong evidence to suggest that the test substance 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate (CAS No. 28510-23-8) is likely to rapidly metabolise in living organisms and has low bioacculumlation.

Additional information

No experimental data evaluating the bioaccumulation potential of 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate (CAS No. 28510-23-8) is available. The substance exhibits a high log Kow (experimental log Kow > 6, calculated log Kow = 7.5), suggesting potential to bioaccumulate in biota. However, the information gathered on environmental behaviour and metabolism, in combination with QSAR-estimated values, provide enough evidence (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. 1907/2006, Annex IX) to state that this substance is likely to show negligible bioaccumulation potential.

Intrinsic properties and fate

2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate is not readily biodegradable but showed high overall degradation rates in an enhanced test on ready biodegradation (Desmares-Koopmans, 2012). Therefore, the substance is expected to undergo ultimate degradation in most environments.

2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate (CAS No. 28510-23-8) exhibits a high log Kow and a water solubility < 0.01 mg/L. The Guidance on information requirements and chemical safety assessment, Chapter R.7b (ECHA, 2012) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Nevertheless, once this contact takes place, these substances are expected to be removed from the water column to a significant degree by adsorption to sewage sludge (Guidance on information requirements and chemical safety assessment, Chapter R.7a, (ECHA, 2012a) and the rest will be biodegraded. Thus, discharged concentrations of these substances into the aqueous compartment are likely to be very low. Should the substances be released into the water phase, due to their hydrophobicity and expected high adsorption potential, they will tend to bind to sediment and other particulate organic matter, and therefore, the actual dissolved fraction available to fish via water will be reduced. Thus, the main route of exposure for aquatic organisms such as fish will be via food ingestion or contact with suspended solids.

QSAR data

Additional information on the bioaccumulation of 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate (CAS No. 28510-23-8) in fish species is available. Estimated bioconcentration (BCF) and bioaccumulation (BAF) values were calculated for this substance using the BCFBAF v3.01 program (Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US EPA), including biotransformation rates (Arnot-Gobas method). The calculated BCF and BAF values are 3.28 L/kg (BCF, regression based estimate) and 15.5/16.5 L/kg (Arnot-Gobas method, BCF and BAF, respectively). The calculations (especially the low BCF values calculated using the Arnot-Gobas method) reflect the rapid biotransformation assumed for 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate. BCF calculations reflect the bioaccumulation potential after uptake via water, whereas the BAF gives an indication of the bioaccumulation when all exposure routes (water, food, etc.) are taken into account.

The obtained results indicate that 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate is likely to show negligible bioaccumulation potential. According to Regulation (EC) No. 1907/2006, Annex XIII, 1.1.2, a substance only fulfills the bioaccumulation criterion (B) when BCF values are > 2000 L/kg. Even though this condition is preferred to be confirmed with experimental data, in this case the estimated QSAR-based BCFs provide sufficient reliable evidence which suggests that the substance will not be bioaccumulative.

Metabolism of 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate

If 2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate is taken up by living organisms, aliphatic esters such as the substance will be initially metabolized via enzymatic hydrolysis to the respective fatty acid and alcohol components as would other dietary fats (e.g., Linfield, 1984). The hydrolysis is catalyzed by carboxylesterases and esterases, with B-esterases located in hepatocytes of mammals being the most important (Heymann, 1980; Anders, 1989). However, carboxylesterase activity has also been reported from a wide variety of tissues in invertebrates and fishes (e.g., Leinweber, 1987; Soldano et al., 1992; Barron et al., 1999; Wheelock et al., 2008). In fish, the high catalytic activity, low substrate specificity and wide distribution of the enzymes in conjunction with a high tissue content lead to a rapid biotransformation of aliphatic esters, which significantly reduces the bioaccumulation potential (Lech & Melancon, 1980; Lech & Bend, 1980).

Metabolites

Neopentyl glycol and 2-ethylhexanoic acid are the expected hydrolysis products from the enzymatic reaction catalyzed by carboxylesterase. REACH registration dossiers of 2-Ethylhexanoic acid and Neopentyl glycol are available and can be publicly viewed on the ECHA webpage (http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances). Both substances are not of concern for the environment.

Conclusion

2,2-dimethylpropane-1,3-diyl 2-ethylhexanoate is not expected to be bioaccumulative. Due to its adsorption properties only low concentrations are expected to be released (if at all) into the environment. Once present in the aquatic compartment, due the high log Koc the substance will be bioavailable to aquatic organisms such as fish mainly via feed and contact with suspended organic particles. After uptake by fish species, extensive and fast biotransformation of the substance into Neopentyl glycol and 2-ethylhexanoic acid is expected. The supporting BCF/BAF values estimated with the BCFBAF v3.01 program also indicate that this substance will not be bioaccumulative (all well below 2000 L/kg).

The information above provides strong evidence supporting the statement that rapid metabolism and low bioaccumulation potential can be expected for this substance.

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