Glycerides, C8-18

Short-term toxicity to aquatic invertebrates

Description of key information

No toxicity up to the limit of water solubility (WS 2-3 mg/L)

Additional information

No experimental data evaluating the acute toxicity of Glycerides, C8-18 (CAS No. 85536-06-7) to aquatic invertebrates are available. Therefore, toxicity data from structurally related category members (Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri-, CAS No. 91052-28-7, Glycerides, C8-C10, mono- and di- (CAS No. 85536-07-8) and Glycerides, C12-18 mono- and di- (CAS No. 91052-49-2) are used as read-across according to Regulation (EC) No. 1907/2006, Annex XI, 1.5. All four substances are esters formed from the combination of fatty acids and glycerol. The target substance contains fatty acids with C-chain lengths ranging from C8 to C18, and >80% triester content. The three read-across substances cover the fatty acid C-chain range of the target substance, being C8-10 for CAS No. 85536-07-8, C12-18 for CAS No. 91052-49-2 and C14-18 (unsaturated) for CAS No. 91052-28-7. The triester content of all three read-across substances is < 15%, being predominantly mono- and diesters. Due to differences on the degree of esterification of these substances with respect to Glycerides, C8-18 (CAS No. 85536-06-7), a higher bioavailability to aquatic organisms can be expected for the read-across substances. Generally, a higher degree of esterification will result in an increase of molecular size and weight of the substance. At higher molecular size and weight, the potential to cross biological membranes tends to decrease (Guidance on information requirements and chemical safety assessment, Chapter R.11 (ECHA, 2012). Furthermore, in a publication by Wu et al. (2006), it was demonstrated that free C18 unsaturated fatty acids were consistently more toxic than C18 saturated fatty acids to aquatic organisms. Considering the high content of C18 unsaturated fatty acids of Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri-, (CAS No. 91052-28-7) and the expected higher bioavailability of the three read-across substances, they represent a worst-case scenario for Glycerides, C8-18 (CAS No. 85536-06-7).

One study evaluating the acute toxicity of Glycerides, C8-C10, mono- and di- (CAS No. 85536-07-8) to aquatic invertebrates is available (Hafner, 2013). This test was performed according to OECD 202, under GLP conditions. Daphnia magna was exposed to the test substance for a period of 48 hours at nominal loading rates ranging from 5.8 mg/L to 300 mg/L (WAF, according to the results of a non-GLP range-finding test). The test was performed under static water conditions.Analytical measurement of the highest (300 mg/L), two middle (62 and 28.2 mg/L) and the lowest (5.8 mg/L) loading rates was performed via TOC and DOC analysis. After the exposure period, 100% immobilization was reported at the 300 mg/L loading rate, whereas no immobilization was observed in any other treatment group. The resulting EL50 (48 h) was determined to be 218.2 mg/L (based loading rate) and the EC50 102.6 mg/L (based on measured test concentration). The acute toxicity of Glycerides, C12-18 mono- and di- (CAS No. 91052-49-2) to aquatic invertebrates was also investigated by Hafner (2012), in a test according to OECD 202, under GLP conditions. Daphnia magna was exposed to the test substance for a period of 48 hours at nominal loading rates ranging from 6.25 mg/L to 100 mg/L (WAF). The test was performed under static water conditions. Analytical measurement of the highest (100 mg/L), middle (25 mg/L) and the lowest (6.25 mg/L) loading rates was performed via TOC and DOC analysis. Mean measured concentrations were determined to be 1.7 mg/L (6.25 mg/L nominal), 4.3 mg/L (25 mg/L nominal) and 14.8 mg/L (100 mg/L nominal). After the exposure period, 95% and 100% immobilization were reported at the highest loading rates of 50 and 100 mg/L, respectively. No immobilization was observed in any other treatment group. The resulting EL50 (48 h) was determined to be 36.2 mg/L (based on loading rate) and the EC50 5.6 mg/L (based on measured test concentration).

 

Nevertheless, the observed immobilization in the two tests mentioned above seems to be caused by direct physical interference of test substance particles with the daphnids, rather than due to toxicity. The measured concentrations at which effects were reported (102.6 mg/L and 5.6 mg/L for CAS No. 85536-07-8 and CAS No. 91052-49-2 respectively) are well above the water solubility of these substances (WS 46 and 3.3 mg/L). For these tests, Water Accommodated Fractions (WAFs) were prepared by adding the test material into a defined volume of test medium, stirring for a period of 48 hours, followed by a sedimentation period of 1 hour. After the sedimentation period, the WAFs with the highest loading rates appeared to be turbid, and in the test conducted with CAS No. 91052-49-2, cloudy cords were observed. In this same test, the next two lower loading rates were also turbid. The test solutions were prepared without a filtration step.

 

Scientific evidence showed that aquatic toxicity testing of this type of Glycerides is technically very difficult. In an article by Prajapati et al. (2012)(see IUCLID section 6.1.4), the phase behaviour of lipid/surfactant/water phases was investigated, where medium-chain (C8-10) mono-, di- and triglycerides represent the lipid. Phase boundaries between lipids (monoglycerides, diglycerides, triglycerides), surfactant (PEG-35 castor oil) and water were established by visual inspection after an equilibration period, and the results expressed in phase diagrams. Viscosity and particle size distribution were measured. The mixtures with monoglyceride displayed two predominant phases: microemulsion and emulsion phases, whereas di- and triglycerides showed additionally a gel phase. Mixtures of monoglycerides and diglycerides, and of monoglycerides and triglycerides seemed to promote an increase of the microemulsion phase (in the 4 phases equilibrium). Particle size in these mixtures was found to be much smaller than in the monoglyceride sample alone. Microemulsions are solutions with an average particle size < 0.2 µm. This particle size would not be intercepted by a standard filter used in an aquatic toxicity test (generally, pore size of 0.45 µm). Due to their small size, based on visual inspection, clear or translucent solutions might be observed even when these microemulsions are present. Glycerides, C8-10 mono- and di- contains mixed mono and diester C8-10 fatty acids, whereas Glycerides, C12-18 mono- and di- contains 40-70% C12 fatty acids. Therefore, formation of microemulsions in test solutions is possible for these substances.

 

Additionally, the acute toxicity of Glycerides, C14-18 and C16-18 unsaturated, mono-, di- and tri- (CAS No. 91052-28-7) to aquatic invertebrates has been evaluated by Salinas (2013). This test was conducted according to OECD 202, under GLP conditions. Daphnia magna was exposed to the substance at a single loading rate of 100 mg/L (nominal, limit test) for 48 hours within a static water regime. At the end of the exposure period, no immobilization was observed. Therefore, the EL50 (48 h) was determined to be > 100 mg/L (nominal, loading rate).

 

Based on the results obtained for the structurally related category members (in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5), no toxicity of Glycerides, C8-C18 (CAS No. 85536-06-7) to aquatic invertebrates up to the limit of the water solubility (2-3 mg/L) is expected.