Glycerides, mixed C8-10 and succinyl

Toxicity to aquatic algae and cyanobacteria

Description of key information

ErL50 (72 h)= 67.6 mg/L (nominal, loading rate)

NOErLR (72 h) = 20.9 mg/L (nominal, loading rate)

NOEC (72 h)    = 1.7 mg/L (mean measured concentration)

Additional information

The toxicity of Glycerides, mixed C8-10 and succinyl (CAS No. 91744-56-8) 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 (Water Accomodated Fraction (WAF)). Analytical measurement of test concentrations was performed via TOC and DOC analysis at the start and at the end of the test. Mean measured concentrations were < 1.02 mg/L (LOQ) in the lowest loading rate (4.3 mg/L), 1.7 mg/L at the 20.7 mg/L loading rate and 3.5 mg/L in the highest loading rate (100 mg/L). Chlorophyll fluorescence was reported as effect parameter, as measure for biomass according to OECD 201.

 

After the exposure period, effects in growth rate were reported at the highest loading rates (45.5 and 100 mg/L, nominal), with inhibition of 24.8% and 74.5%, respectively. No effects were observed at lower loading rates (20.7, 9.4 and 4.3 mg/L). The resulting EL50 value (72 h) was determined to be 67.6 mg/L (based on growth rate, nominal loading rate) and the NOEC (72 h) was 20.7 mg/L (nominal, loading rate), 1.7 mg/L (mean measured concentration).

 

Nevertheless, the observed effects are above the water solubility of the substance and might be caused by direct physical interference of test substance particles with algae cells, rather than intrinsic toxicity. The Water Accommodated Fractions (WAFs) were prepared by adding the test material into water, stirring for a period of 48 hours, followed by a sedimentation period of 1 hour. After the sedimentation period, although no particles in suspension were observed, the WAFs were not completely clear. The test solutions were prepared without a further filtration step. The results from the analytical measurement of test concentrations show that the test item was only sparingly soluble. According to the authors of the report, at the highest loading rates, cell growth was suppressed already after 24 and 48 hours at 100 mg/L and 45.5 mg/L, respectively. Microscopic observations at the end of the test (72 h) confirmed that in these two groups there were almost no algae. Their conclusion is that physical effects due to absorption of chlorophyll fluorescence radiation by the test item, or other physical effects on the cells caused by emulsified test item 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 microemulsions are present. Glycerides, mixed C8-10 and succinyl contains mixed C8-10 fatty acids mono-, di- and triester and formation of microemulsions in test solutions is therefore possible.

 

Based on the above information and considering that the observed effects occurred above the water solubility of the substance (1-2 mg/L), these 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, mixed C8-10 and succinyl is thus expected. Nevertheless, since the NOEC value based on mean measured concentration is within the water solubility range of the substance, 1.7 mg/L, this value is used for PNEC derivation as a worst-case approach.