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Long-term toxicity to aquatic invertebrates

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Description of key information

The chemical safety assessment according to Annex I does not indicate the need to conduct long-term toxicity testing on aquatic invertebrates

Key value for chemical safety assessment

Additional information

No experimental data evaluating the chronic toxicity of Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8) to aquatic invertebrates are available. According to Regulation (EC) No. 1907/2006, Annex IX, 9.1.5, long-term toxicity testing shall be proposed by the registrant if the chemical safety assessment according to Annex I indicates the need to investigate further the effects on aquatic organisms. This is not the case for Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8), as all available information indicates no concern related to long-term toxicity, as discussed below.

 

Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8) is readily biodegradable (81.7% biodegradation in 28 days) and it has a high potential for adsorption (log Kow > 10). 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, according to the Guidance on information requirements and chemical safety assessment, Chapter R7.c (ECHA, 2012), the potential for bioaccumulation can be estimated from the log Kow value of the substance as a screening approach. Generally, at log Kow values > 6 a decrease in BCF values is observed, probably caused by the reduced uptake with the expected increasing molecular size of such substances. Even though experimental data evaluating bioaccumulation for substances with log Kow > 10 is not known, these substances are expected to have BCF values < 2000 L/kg (criterion used to consider a substance Bioaccumulative)(Guidance on information requirements and chemical safety assessment, Chapter 11 (ECHA, 2012). The metabolization of Glycerides, mixed C8-10 and succinyl in aquatic organisms via enzymatic hydrolysis is expected to result in C8 and C10 fatty acids, glycerol and succinic acid 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). Moreover, succinic acid is naturally present in mammals and fish. The combination of its ionized form (succinate) with coenzyme A (CoA) plays a major role as intermediate in the citric acid cycle (succinyl-CoA)(Lehninger, Nelson and Cox (1994); De Silva and Anderson, 1995). Therefore, it is expected to be extensively metabolized and not bioaccumulated in aquatic organisms. 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, mixed C8-10 and succinyl in aquatic organisms can be expected.

 

The acute toxicity studies conducted with Glycerides, mixed C8-10 and succinyl on aquatic invertebrates and fish species showed no effects of the substance up to the limit of its water solubility (1-2 mg/L), with EL50 and LL50 values > 100 mg/L and > 70 mg/L (loading rates), corresponding to measured concentrations > 10.7 mg/L and > 2.0 mg/L, respectively. Effects on growth rate were reported on the test conducted with algae, resulting in an EL50 (72 h) of 67.7 mg/L (loading rate) and a NOEC (72 h) of 20.9 mg/L (loading rate, corresponding to a mean measured concentration of 1.7 mg/L). Nevertheless, the report available for this study states that the possibility of physical effects (due to disturbance of algae cells by emulsified test substance) instead of, or in addition to toxicological effects cannot be excluded. The test material was reported to be sparingly soluble and therefore Water Accomodated Fractions (WAFs) were prepared. The WAFs were stirred for 48 hours and thereafter left for sedimentation for a period of 1 hour. After the sedimentation period, the WAFs were not completely clear. Filtration of the WAFs for the preparation of final test solutions was not performed. The observed effects occurred above the water solubility of the substance (WS 1-2 mg/L), nevertheless the NOEC based on measured mean concentration is 1.7 mg/L, within the water solubility range. Therefore, this value is used for PNEC derivation as a worst-case approach.

 

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 microemulsions are present. Glycerides, mixed C8-10 and succinyl contains mixed C8-10 fatty acids mono-, di- and triester and formation of microemulsions in test solutions is therefore possible. The only test conducted with this substance showing effects was the algae test, in which the WAFs were reported to be not completely clear, even though suspended particles could not be directly observed. This is considered as an indication of a microemulsion-formation phase, showing that the observed effects in the algae test 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, mixed C8-10 and succinyl is toxic to fish and aquatic invertebrates, whereas a NOEC value is available for the species showing the highest sensitivity (algae).

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), 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, mixed C8-10 and succinyl (CAS No. 91744-56-8).

 

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

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