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Short-term toxicity to aquatic invertebrates

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Description of key information

EL50 (48 h) = 36.2 mg/L (nominal, loading rate)
EC50 (48 h) = 5.6 mg/L (measured concentration)

Key value for chemical safety assessment

Additional information

No experimental data investigating the acute toxicity of Glycerides, C12-18 di- and tri- (CAS No. 91744-28-4) to aquatic invertebrates are available. Therefore, toxicity data from a structurally related category member (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. Both substances are esters formed from the combination of C12-18 fatty acids and glycerol. Due to differences on the degree of esterification of these substances (mono- and diester for CAS No. 91052-49-2, and di- and triester for CAS No. 91744-28-4), a higher bioavailability to aquatic organisms can be expected for the source substance (CAS No. 91052-49-2). 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). Considering this information, reading across from Glycerides, C12-18 mono- and di- represents a worst-case scenario for the target substance and therefore it is justified.

The acute toxicity of Glycerides, C12-18 mono- and di- (CAS No. 91052-49-2) to aquatic invertebrates is available (Hafner, 2012). 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 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 5.6 mg/L (based on measured test concentration).

 

Nevertheless, the observed effects might be caused by direct physical interference of test substance particles with test organisms (i.e. physical entrapment), rather than intrinsic toxicity. For this test, 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 WAF with the highest loading rate (100 mg/L) appeared to be inhomogeneous and presented cloudy cords. The next two lower loading rates (25 and 50 mg/L) were 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, C12-18 di- and tri- contains 40-65% C12 fatty acids and formation of microemulsions in test solutions is therefore possible for this substance.

 

Based on the above information, the observed effects are expected to be caused by physical entrapment of Daphnia rather than due to intrinsic toxicity of the substance. No toxicity up to the highest attainable solubility (before microemulsion formation) of Glycerides, C12-18 di- and tri- is thus expected. Nevertheless, since the EL50 value is within the water solubility range of the substance, 5.6 mg/L (measured concentration), this value is considered for hazard assessment as worst-case approach.