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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The bioaccumulation potential is expected to be low.

Key value for chemical safety assessment

Additional information

No experimental data is available concerning the bioaccumulation potential of Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates (CAS-No. 91052 -13 -0). Therefore, all available related data are combined in a Weight of Evidence approach (WoE), which is in accordance to Regulation (EC) No. 1907/2006, Annex XI General rules for adaptation of the standard testing regime set out in Annexes VII to X, 1.2, to cover the data requirements of Annex IX and X.

Bioaccumulation refers to the uptake of a substance from all environmental sources including water, food and sediment. However, the accumulation of a substance in an organism is determined, not only by uptake, but also by distribution, metabolism and excretion. Accumulation takes place if the substance is taken up faster than it can be metabolised and/or excreted.

 

Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates exhibits a log Koc value of > 3. Therefore, a significant degree of removal of the substance from the water column due to adsorption 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.

Should the substance be released into the water phase, it will be bioavailable to aquatic organisms partially via water and partially via feed and contact with suspended solids. Absorbed molecules of the substance will be metabolized. After lipid content, the degree of biotransformation seems to be the most relevant factor regarding the bioaccumulation of organic chemicals in aquatic organisms (Katagi, 2010). Biotransformation consists in the conversion of a specific substance into another/other (metabolites) by means of enzyme-catalyzed processes (ed. van Leeuwen and Hermens, 1995). Carboxylesterases are a group of ubiquitous and low substrate specific enzymes, involved in the metabolism of ester compounds in both vertebrate and invertebrate species, including fish (Leinweber, 1987; Barron et al., 1999).

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-sterified once more with glycerol and partial acyl glycerols to form triglycerides, that 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 (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).

Therefore, Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates is likely to be rapidly metabolised, and therefore, concentrations stored in aquatic organisms will tend to be low.

This assumption is supported by QSAR calculations using BCFBAF v3.01 performed for Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates. BCF/BAF values of 9.44-12.3 L/kg were obtained for the substance (Arnot-Gobas estimate, including biotransformation, upper trophic).  

Conclusion

Due to its log Koc value of > 3, significant adsorption of this substance to activated sludge 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, the substance will be bioavailable to aquatic organisms partially via water and partially via feed and contact with suspended solids. Nevertheless, absorbed molecules of the substance will be metabolized. The bioaccumulation potential of this substance is thus expected to be low. BCF/BAF values estimated by QSAR (BCFBAF v3.01) also support this assumption (BCF values 9.44-12.3 L/kg).

Taking all these information into account, it can be concluded that bioaccumulation of Glycerides, C8-18 and C18-unsatd. mono- and di-, acetates (CAS-No. 91052 -13 -0) is expected to be low.