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Toxicity to aquatic algae and cyanobacteria

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Description of key information

ErL50 (72 h)= 49 mg/L (nominal, loading rate)
NOErLR (72 h) = 20.7 mg/L (nominal, loading rate)
NOEC (72 h) = 1.19 mg/L (measured concentration)

Key value for chemical safety assessment

Additional information

The toxicity of Glycerides, C8-C10, mono- and di- (CAS No. 85536-07-8) to algae was evaluated in a study by Hafner (2013). This test was conducted according to OECD 201, under GLP conditions. Desmodesmus subspicatus was exposed to the test substance for 72 hours at nominal loading rates ranging from 4.3 to 100 mg/L (WAF). Analytical measurement of test concentrations was performed via TOC and DOC analysis. After the exposure period, significant effects in growth rate were reported at the highest loading rates (45.5 and 100 mg/L, nominal). The resulting EL50 value (72 h) was determined to be 49 mg/L (based on growth rate, loading rate). The NOELR (72 h) was 20.7 mg/L (based on growth rate, loading rate) and 1.19 mg/L (based on growth rate, measured final concentration).

 

Nevertheless, the observed effects might be caused by direct physical interference of test substance particles with algae cells, 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 65 minutes. After the sedimentation period, all WAFs contained white flakes, which sedimented. The WAFs were not filtered for the final test. According to the authors of the report, at the highest loading rates (45.5 mg/L and 100 mg/L, for which effects were observed), algae were encased by small dispersed particles in the suspension. This was confirmed by microscopic observation. In the two lower loading rates (4.3 and 9.4 mg/L) no difference compared to the control vessels were observed. In the middle loading rate (20.7 mg/L nominal) cell count was lower and the cell shape was smaller compared to the control. In the second highest loading rate (45.5 mg/L) almost no algal cells could be observed anymore. The remaining cells formed piles which are typical for stress situations. In the highest loading rate (100 mg/L), no algal cells were observed but the whole microscope slide was coated with small oily drops with similar size to that of the algal cells. Therefore, a mechanical disturbance of cells and cell growth cannot be excluded.

 

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 mono and diester C8-10 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 mechanical disturbance of the algae cells rather than due to intrinsic toxicity of the substance. No toxicity up to the highest attainable solubility (before microemulsion formation) of Glycerides, C8-10 mono- and di- is thus expected. Nevertheless, since the NOEC value is within the water solubility range of the substance, 1.19 mg/L (measured concentration), this value is used for PNEC derivation as a worst-case approach.

 

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