Glycerides, C8-18

Long-term toxicity to aquatic invertebrates

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 aquatic invertebrates.

Additional information

No experimental data evaluating the chronic toxicity of Glycerides, C8-18 (CAS No. 85536-06-7) to aquatic invertebrates are available. Therefore, toxicity data from a structurally related category member (Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri-, CAS No. 91052-28-7) are used as read-across according to Regulation (EC) No. 1907/2006, Annex XI, 1.5. Both substances are esters formed from the combination of fatty acids and glycerol. The target substance contains fatty acids with C-chain lengths ranging from C8 to C18, and >80% triester content, whereas CAS No. 91052-28-7 contains C14-18 (unsaturated) fatty acids, and a triester content < 15%. Due to differences on the degree of esterification of the read-across substance with respect to Glycerides, C8-18 (CAS No. 85536-06-7), a higher bioavailability to aquatic organisms can be expected for CAS No. 91052-28-7. Generally, a higher degree of esterification will result in an increase of molecular size and weight of the substance. At higher molecular size and weight, the potential to cross biological membranes tends to decrease (Guidance on information requirements and chemical safety assessment, Chapter R.11 (ECHA, 2012). Furthermore, in a publication by Wu et al. (2006), it was demonstrated that free C18 unsaturated fatty acids were consistently more toxic than C18 saturated fatty acids to aquatic organisms. Considering the high content of C18 unsaturated fatty acids of Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri-, (CAS No. 91052-28-7) and the expected higher bioavailability to aquatic organisms, this substance represents a worst-case scenario for Glycerides, C8-18 (CAS No. 85536-06-7).

The chronic toxicity of Glycerides, C14-18 and C16-18 unsaturated, mono-, di- and tri- (CAS No. 91052-28-7) to aquatic invertebrates has been evaluated by Salinas (2013). This test was conducted according to OECD 211, under GLP conditions. Daphnia magna was exposed to the substance at a single loading rate of 10 mg/L (limit test) for 21 days within a semi-static water regime. At the end of the exposure period, no effects on survival, reproduction or any other adverse effects were reported. Therefore the NOELR was determined to be ≥ 10 mg/L (nominal, loading rate).

 

There are no studies available investigating the chronic toxicity of substances containing C8-10 fatty acids (such as Glycerides, C8-18 (CAS No. 85536-06-7) to aquatic invertebrates. In view of the results of the acute studies conducted with suitable read-across substances, no toxicity to aquatic invertebrates up to the limit of the water solubility (2-3 mg/L) of Glycerides, C8-18 is expected. The acute studies do not show a clear trend of higher toxicity of the shorter-chain Glycerides, however, studies with these substances seem to be more difficult to perform, due to the interference of physical effects. Scientific evidence showed that aquatic toxicity testing of this type of Glycerides is technically very difficult. In an article by Prajapati et al. (2012)(see IUCLID section 6.1.4), the phase behaviour of lipid/surfactant/water phases was investigated, where medium-chain (C8-10) mono-, di- and triglycerides represent the lipid. Phase boundaries between lipids (monoglycerides, diglycerides, triglycerides), surfactant (PEG-35 castor oil) and water were established by visual inspection after an equilibration period, and the results expressed in phase diagrams. Viscosity and particle size distribution were measured. The mixtures with monoglyceride displayed two predominant phases: microemulsion and emulsion phases, whereas di- and triglycerides showed additionally a gel phase. Mixtures of monoglycerides and diglycerides, and of monoglycerides and triglycerides seemed to promote an increase of the microemulsion phase (in the 4 phases equilibrium). Particle size in these mixtures was found to be much smaller than in the monoglyceride sample alone. Microemulsions are solutions with an average particle size < 0.2 µm. This particle size would not be intercepted by a standard filter used in an aquatic toxicity test (generally, pore size of 0.45 µm). Due to their small size, based on visual inspection, clear or translucent solutions might be observed even when these microemulsions are present. The WAFs at which effects were observed in the three acute tests conducted with the read-across substance Glycerides C8-10 mono- and di- (fish, aquatic invertebrates and algae) were reported to be turbid, even though suspended particles could not be directly observed in the fish and aquatic invertebrates tests. This is considered as an indication of a microemulsion-formation phase, showing that the observed effects might indeed be due to physical interference with emulsified test material. The chances of microemulsion formation under chronic exposure to this substance are very high. Due to the prolonged testing period for these long-term toxicity tests, microemulsions can cause physical effects on fish (e.g gill clogging) and aquatic invertebrates (e.g. physical entrapment). Therefore, obtaining reliable chronic values out of such tests is technically difficult. Furthermore, based on the results of the acute tests, there is no indication showing that Glycerides, C8-18 would be toxic to fish or aquatic invertebrates up to the limit of its water solubility (2-3 mg/L), whereas a NOEC value is available for the species showing the highest sensitivity (algae).

 

Glycerides, C8-18 (CAS No. 85536-06-7) is readily biodegradable and it has high potential for adsorption (log Koc values 0.42-14.2). According to the Guidance on information requirements and chemical safety assessment, Chapter R.7b, readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs)(ECHA, 2012). Besides being extensively biodegraded in STPs (due to its ready biodegradability), a significant degree of removal of this substance from the water column due to adsorption to sewage sludge can be expected (Guidance on information requirements and chemical safety assessment, Chapter R.7a (ECHA, 2012)). Therefore, after passing through conventional STPs, only low concentrations of these substances are likely to be (if at all) released into the environment.

 

Moreover, rapid metabolization of Glycerides, C8-C18 in aquatic organisms is expected. Enzymatic hydrolysis is expected to result in C8-18 fatty acids and glycerol as transformation products. Part of the free fatty acids will be re-esterified with glycerol and partial acyl glycerols to form triglycerides that will be stored as long-term energy reserves (Tocher, 2003). Glycerol is naturally present in animal and vegetable fats, rarely found in free state (mostly combined with fatty acids forming triglycerides) (ed. Knothe, van Gerpen and Krahl, 2005). If freely available in aquatic organisms, it will not bioaccumulate in view of its log Kow value of -1.76 (OECD SIDS, 2002). Especially in periods in which the energy demand is high (reproduction, migration, etc.), glycerides are mobilized from the storage sites as source of fatty acids. Fatty acid catabolism is the most important energy source in many species of fish, resulting in the release of acetyl CoA and NADH (through β-oxidation) and eventually, via the tricarboxylic cycle, the production of metabolic energy in the form of ATP. This fatty acid-catabolism pathway is the predominant source of energy related to growth, reproduction and development from egg to adult fish. A similar metabolic pathway is observed in mammals (see section 7.1.1 Basic toxicokinetics). According to the Guidance on information requirements and chemical safety assessment, Chapter R.7c (ECHA, 2012), even though ready biodegradability does not per se preclude bioaccumulation potential, generally (depending on exposure and uptake rates) ready biodegradable substances are likely to be rapidly metabolised, and therefore, concentrations stored in aquatic organisms will tend to be low. Considering the above information, low bioaccumulation potential of Glycerides, C8-C18 in aquatic organisms can be expected.

 

Considering the expected low bioavailability of the substance in water, its low bioaccumulation potential, the technical difficulties involved in aquatic toxicity testing of Glycerides C8-10 (due to their tendency to form microemulsions), the result of the test conducted with CAS No. 91052-28-7 (NOELR (21 d) > 10 mg/L) and the fact that a NOEC value is available for the species showing the highest sensitivity (algae), long-term toxicity testing is not deemed necessary for Glycerides, C8-18 (CAS No. 85536-06-7).

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