Glycerides, mixed C8-10 and succinyl

Sediment toxicity

Description of key information

The chemical safety assessment according to Annex I does not indicate the need to conduct a test on sediment organisms

Additional information

No experimental data evaluating the toxicity to sediment organisms is available for Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8). Since the substance is readily biodegradable, exposure of sediment organisms is the aquatic environment is unlikely. Furthermore, the substance showed no toxicity to fish and aquatic invertebrates up to the limit of water solubility. Low toxicity was reported for algae species, leading to a NOELR = 20.9 mg/L (loading rate), corresponding to a mean measured concentration of 1.7 mg/L. Nevertheless, since the effects are above the water solubility of the substance, physical effects due to interference or adsorption of the substance to algae cells cannot be excluded. In addition, available data indicate that Glycerides, mixed C8-10 and succinyl is not bioaccumulative. Based on the available information, toxicity to sediment organisms is not expected to be of concern.

 

Intrinsic properties and fate

Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8) is readily biodegradable.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). Therefore, after passing through conventional STPs, only low concentrations of this substance are likely to be (if at all) released into the environment.

The water solubility of Glycerides, mixed C8-10 and succinyl was determined to be 1-2 mg/L (at 20°C). On the other hand, the log Pow value (> 10) indicates high adsorption potential of the substance to solid particles. Therefore, 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)). Discharged concentrations into the aquatic compartment are therefore likely to be low.

 

Considering the above information, the availability of Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8) in the sediment environment is expected to be very low, which reduces the probability of sediment organisms exposure.

 

Aquatic toxicity

Aquatic toxicity tests performed on fish and aquatic invertebrates showed no adverse effects occurred in the range of the water solubility of the substance (1-2 mg/L). Low toxicity was reported for algae species, leading to a NOELR (72 h) = 20.9 mg/L (loading rate), corresponding to a mean measured concentration of 1.7 mg/L. Nevertheless, since the observed effects are above the water solubility of the substance, physical effects due to interference or adsorption of the substance to algae cells cannot be excluded.

 

The obtained results indicate that Glycerides, mixed C8-10 and succinyl is likely to show no or only low toxicity to sediment organisms as well.

Metabolism/Bioaccumulation

After uptake,Glycerides, mixed C8-10 and succinyl is expected to be enzymatically hydrolyzed by carboxylesterases. QSAR estimations using BCFBAF v3.01 support the expected rapid biotransformation of this substance with BCF/BAF ranging from 0.89-1 L/kg.

 

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 (throughβ-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 thoughready biodegradability does not per se preclude bioaccumulation potential, generally (depending on exposure and uptake rates) ready biodegradable substancesare likely to be rapidly metabolised, and therefore, concentrations stored in aquatic organisms will tend to be low.

 

In conclusion, low bioaccumulation potential of Glycerides, mixed C8-10 and succinyl is expected.

Conclusion

Due to its readily biodegradable nature, extensive degradation of this substance in conventional STPs will take place and only low concentrations are expected to be released (if at all) into the environment. Once present in the aquatic compartment, further biodegradation will occur and, due to the high adsorption potential, Glycerides, mixed C8-10 and succinyl will be bioavailable to sediment organisms mainly via feed and contact with suspended organic particles.After uptake by sediment species, extensive and fast biotransformation of the substance by carboxylesterases into fatty acids, glycerol and succinic acid is expected. The supporting BCF/BAF values estimated with the BCFBAFv3.01 program, Arnot-Gobas model including biotransformation, also indicate that this substance will not be bioaccumulative (0.89-1 L/kg). Furthermore, based on the aquatic toxicity data, the toxicity to aquatic organisms is expected to be low (if observed at all). Therefore, Glycerides, mixed C8-10 and succinyl is unlikely to pose a risk for sediment organisms in general and testing is thus omitted.

 

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