Isooctadecanoic acid, monoester with glycerol

Bioaccumulation: aquatic / sediment

Description of key information

The potential for bioaccumulation is expected to be low. 

Additional information

Experimental data investigating the bioaccumulation potential of Glycerol monoisostearate (CAS 66085-00-5) are not available. The substance has a log Pow > 6.54 indicating a potential to bioaccumulate in biota. However, the information gathered on environmental behaviour and metabolism in combination with the QSAR-estimated BCF values provide enough evidence (in accordance with REACh 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 Regulation (EC) No. 1907/2006, Annex IX) to state that the substances is not likely to bioaccumulate. The substance is considered to be readily biodegradable and is insoluble in water (water solubility < 0.05 mg/L). 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). The guidance document states furthermore 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 (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.
If released to the water the substance will tend to bind to sediment and other particulate organic matter due to their hydrophobicity and relatively high adsorption potential. The actual dissolved fraction available to fish via water is assumed to be low (Mackay and Fraser, 2000). Thus, the most relevant exposure route for aquatic organisms such as fish will be via food ingestion or contact with suspended solids. If the substance is ingested by organisms a fast metabolisation is expected. 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 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-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 (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). According to the Guidance on information requirements and chemical safety assessment, Chapter R.7c (ECHA, 2012), even though ready biodegradability does not per se preclude bioaccumulation potential, generally (depending on exposure and uptake rates) ready biodegradable substances are likely to be rapidly metabolised, and therefore, concentrations stored in aquatic organisms will tend to be low. Additional information on the bioaccumulation of Glycerides in fish species is available. Estimated bioconcentration (BCF) and bioaccumulation (BAF) values were calculated for the substance using the BCFBAF v3.01 program (Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US EPA), assuming biotransformation (Arnot-Gobas method). The estimated BCF values for the main substance components ranged from 0.893 – 36.6 L/kg. Even though not all components are within the applicability domain of the model (covering substances with log Kow values in the range 0.31-8.70), the estimated values can be considered as supporting data indicating low bioaccumulation of the substance.
Conclusion
The substance Glycerol monoisostearate (CAS 66085-00-5) is not expected to be bioaccumulative. Due to the ready biodegradability, extensive degradation of the substance in conventional STPs will take place and only low concentrations are expected to be released (if at all) to the environment. Once present in the aquatic compartment the substance will be further degraded. If the substance is taken up by fish species, extensive and fast biotransformation of the Glycerides by carboxylesterases into fatty acids and glycerol is expected. Fatty acids will be further used by these organisms as their main source of energy throughout all the different life stages (early development, growth, reproduction, etc.). The supporting BCF/BAF values estimated with the BCFBAF v3.01 program also indicate that the substance has a low bioaccumulation potential.  The composition of the substance includes the mono- di- and tri-glyceride of isostearate. For each of these forms, the iso-branching may be present as a methyl-, ethyl or propyl-branching, although the branching is always simple. For the calculation of the BCF/BAF values only the methyl branching was considered since the calculation with QSAR (BCFBAF v3.01) revealed very similar or equal results for the branching types.

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