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Sediment toxicity

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Description of key information

Taking all available information into account the Glyceride category members are unlikely to pose a risk for sediment organisms and testing is thus omitted.

Key value for chemical safety assessment

Additional information

No experimental data evaluating the toxicity to sediment organisms are available for Glycerides, C16-18 and C18-unsatd. mono- (CAS No. 91744-09-1). Since the substance is readily biodegradable, exposure of sediment organisms is unlikely. Furthermore, the substance showed no toxicity to fish, aquatic invertebrates and algae up to the limit of water solubility. In addition, available data indicate that Glycerides, C16-18 mono- is not bioaccumulative. Based on the available information, toxicity to sediment organisms is not expected to be of concern.

 

Intrinsic properties and fate

Glycerides, C16-18 and C18-unsatd. mono- 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 these substances are likely to be (if at all) released into the environment.

Furthermore, the substance exhibits a log Kow value > 5 and is poorly soluble in water (< 0.41 mg/L). The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2012) 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. Nevertheless, once this contact takes place, these substances are expected to be removed from the water column to a significant degree by adsorption to sewage sludge (Guidance on information requirements and chemical safety assessment, Chapter R.7a, (ECHA, 2012)) 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, one can assume that the availability of Glycerides, C16-18 and C18-unsatd. mono- in the sediment environment is generally very low, which reduces the probability of exposure of sediment organisms in general.

 

Aquatic ecotoxicity data

Acute and chronic aquatic toxicity tests (read-across data) performed on fish, aquatic invertebrates and algae showed no adverse effects occurred in the range of the water solubility of the substance. 

The obtained results indicate that Glycerides, C16-18 and C18-unsatd. mono- is likely to show no or only low toxicity to sediment organisms as well.

 

Metabolism/Bioaccumulation

After uptake, Glycerides, C16-18 and C18-unsatd. mono- is expected to be enzymatically hydrolyzed by carboxylesterases yielding the corresponding alcohol and fatty acids. QSAR estimations using BCFBAF v3.01 support the expected rapid biotransformation of this substance with BCF/BAF of 34.81-38.13/34.81-38.34 L/kg.

The metabolism of the hydrolysisproducts: 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 hydrolized 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 Glycerides, C16-18 and C18-unsatd. mono- .

 

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 log Kow, low water solubility and high adsorption potential, Glycerides, C16-18 and C18-unsatd. mono- 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 and glycerol 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. Furthermore, based on the aquatic toxicity data, the toxicity to aquatic organisms is expected to be low. Therefore, Glycerides, C16-18 and C18-unsatd. mono- is unlikely to pose a risk for sediment organisms in general and testing is thus omitted.