Glycerol trioctanoate

Sediment toxicity

Additional information

Taking all available information into account,Glycerol trioctanoate (CAS 538-23-8)is unlikely to pose a risk to sediment organisms and testing is thus omitted.

No experimental data evaluating the toxicity to sediment organisms are available forGlycerol trioctanoate (CAS 538-23-8). Only negligible releases into surface waters from sewage treatment plants are expected to take place due to the ready biodegradability and the high adsorption potential of this substance, resulting in an effective removal in sewage treatment plants. Therefore, chronic exposure of sediment organisms is unlikely. Furthermore, the substance is not toxic to aquatic organisms up to the limit of water solubility. In addition, bioaccumulation of the substance is not relevant. Based on the available information, toxicity to sediment organisms is not expected to be of concern.

Intrinsic properties and fate

Glycerol trioctanoate (CAS 538-23-8) is predicted to be readily biodegradable based on read-across. 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) (Guidance on information requirements and chemical safety assessment, Chapter R.7a, ECHA, 2017a). Therefore, after passing through conventional STPs, only low concentrations of these substances are likely to be (if at all) released into the environment.

Furthermore, the substance is poorly soluble in water (< 0.532 µg/L at 20 °C). The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2017b) 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. (Guidance on information requirements and chemical safety assessment, Chapter R.7a, (ECHA, 2017a)) and the rest will be extensively biodegraded (due to ready biodegradability). Thus, discharged concentrations of these substances into the aqueous/sediment compartment are likely to be negligible. Considering this, it can be assumed that the availability of Glycerol trioctanoate (CAS 538-23-8) in the sediment environment is generally very low, which reduces the probability of exposure of sediment organisms in general.

Aquatic ecotoxicity data

Based on experimental data from structurally related read-across substances with similar ecotoxicological profiles, it can be predicted that Glycerol trioctanoate (CAS 538-23-8) shows no acute and long-term toxicity test to aquatic invertebrates, no toxicity to algae and no short-term toxicity to fish up to the limit of water solubility (< 0.532 µg/L). Furthermore, based on the toxicity control from a ready biodegradability study of a structurally related read-across substance, Glycerol trioctanoate (CAS 538-23-8) can be predicted to be non-inhibitory to microorganisms. The obtained results from this read-across indicate that Glycerol trioctanoate (CAS 538-23-8) is likely to show no or only low toxicity to sediment organisms either.

Metabolism/Bioaccumulation

After uptake, Glycerol trioctanoate (CAS 538-23-8) is expected to be enzymatically hydrolysed by carboxylesterases yielding the corresponding alcohol and fatty acids. The metabolism of the hydrolysis products alcohol (i.e. glycerol) and fatty acids is well established and not of concern in terms of bioaccumulation. Glycerides, especially triglycerides, are the predominant lipid class in the diet of both marine and freshwater fish. Once ingested, they will be hydrolysed into fatty acids and glycerol by a specific group of carboxylesterase (CaE) enzymes (lipases) as reported in different fish species (Tocher, 2003). Part of the free fatty acids will be re-esterified once more with glycerol and partial acyl glycerols to form triglycerides, which will be stored as long-term energy reserves. 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). In conclusion, no potential for bioaccumulation is to be expected for Glycerol trioctanoate (CAS 538-23-8).

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. If the substance is taken up by sediment organisms, extensive and fast biotransformation of the substance by carboxylesterases into fatty acids and glycerol is expected. Furthermore, based on the aquatic toxicity data from structurally related read-across substances, the toxicity to aquatic organisms is expected to be low. Therefore Glycerol trioctanoate (CAS 538-23-8) is unlikely to pose a risk to sediment organisms.

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