Glycerol trimyristate

Sediment toxicity

Additional information

According to Annex VII of Regulation (EC) No 1907/2006, the generation of sediment data is not required. Sediment toxicity is contemplated since the physico-chemical properties of Glycerol trimyristate (CAS 555-45-3) indicate a possible distribution to the sediment. Experimental data evaluating the toxicity of the substance to sediment organisms are not available. Since the substance is readily biodegradable, exposure of sediment organisms is unlikely. Furthermore, the substance showed no toxicity to aquatic invertebrates and algae up to the limit of water solubility. Based on the available information, toxicity to sediment organisms is not expected to be of concern.

Intrinsic properties and fate

Glycerol trimyristate (CAS 555-45-3) 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) (Guidance on information requirements and chemical safety assessment, Chapter R.7a, ECHA, 2017). 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 (≤ 1.63 µg/L). The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2017) 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, 2017)) 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 trimyristate (CAS 555-45-3) in the sediment environment is generally very low, which reduces the probability of exposure of sediment organisms in general.

Aquatic ecotoxicity data

Acute aquatic toxicity tests (read-across data) performed with aquatic invertebrates and algae showed no adverse effects occurred in the range of the water solubility of the substance. The obtained results indicate that Glycerol trimyristate (CAS 555-45-3) is likely to show no or only low toxicity to sediment organisms as well.

Metabolism/Bioaccumulation

After uptake, Glycerol trimyristate (CAS 555-45-3) 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 trimyristate (CAS 555-45-3).

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, the toxicity to aquatic organisms is expected to be low. Therefore Glycerol trimyristate (CAS 555-45-3) is unlikely to pose a risk to sediment organisms.