Fatty acids, C6-18, 2,2-dimethyl-1,3-propanediyl esters

Long-term toxicity to fish

Description of key information

The chemical safety assessment according to Annex I of Regulation (EC) No. 1907/2006 does not indicate the need to investigate further the long-term toxicity to fish. Thus, in accordance to Annex IX, column 2 no further long-term toxicity test to fish is proposed.

Additional information

There are no long-term fish studies available for the NPG esters group. However, in short-term studies, available for all three trophic levels, fish, daphnia and algae, no effects were observed up to the limit of water solubility. Based on the short-term values, fish cannot be identified as the most sensitive taxonomic group. According to the “Guidance on information requirements and chemical safety assessment Chapter R.7b: Endpoint specific guidance, R.7.8.5.3” (ECHA, 2012), long-term testing of fish should only be conducted if it represents the most sensitive taxonomic group. The Guidance states that if invertebrates are likely to be more sensitive than fish and algae or the relative sensitivity of invertebrates cannot be predicted, long-term testing on Daphnia sp. should be preferred instead of fish. Two long-term studies with Daphnia magna are available for the NPG esters Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol (CAS No. 68855-18-5) and 2,2-dimethyl-1,3-propanediyl dioleate (CAS No. 42222-50-4). These test substances represent both ends of the NPG group and are sufficient for the assessment of long-term aquatic toxicity for all NPG esters.

Furthermore, the aquatic concentrations of the NPG esters are expected to be very low. Since the substances are readily biodegradable and have high adsorption potential, they will be eliminated in sewage treatment plants to a high extent. If fractions of these chemicals were to be released in the aquatic environment, the concentration in the water phase will be reduced by rapid biodegradation and potential of adsorption to solid particles and to sediment.

Food ingestion is likely to be the main uptake route for NPG esters in fish, since the substance will be adsorbed to solid particles potentially ingested by fish. In the case of ingestion, NPG esters are predicted to undergo metabolism. Esters are known to hydrolyse into carboxylic acids and alcohols by esterases (Fukami and Yokoi, 2012). The result of the pancreatic digestion of the NPG group member 2,3-dimethyl-1,3 –propandiolheptanoate (CAS No. 68855-18-5) shows a degradation of the ester of almost 90% within 4 hours (Oßberger, 2012; IUCLID section 7.1.1). 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). Therefore, it is expected that under physiological conditions, NPG esters will hydrolyse to neopentyl glycol and the respective fatty acids. Neopentyl glycol undergoes to conjugation with glucuronic acid and be excreted in the urine (Gessner, 1960).The free fatty acids are either metabolised via the β-oxidation pathway in order to generate energy for the cell or reconstituted into glyceride esters and stored in the fat depots in the body (Berg, 2002). Metabolic pathways in fish are generally similar to those in mammals. Lipids and their constituents, fatty acids, are in particularly a major organic constituent of fish and play a crucial role as source of metabolic energy in fish, for growth, reproduction and mobility, including migration (Tocher, 2003).

In conclusion, NPG esters will be mainly taken up by ingestion and are digested through common metabolic pathways, providing a valuable energy source for fish, as dietary fats. Based on this information presently available, long-term toxicity to fish is not to be expected.

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