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Toxicity to aquatic algae and cyanobacteria

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Description of key information

ErL50 (72 h) > 320 mg/L (nominal, loading rate) for Desmodesmus subspicatus (OECD 201)
NOELR (72 h) = 32 mg/L (nominal, loading rate) for Desmodesmus subspicatus (OECD 201)

Key value for chemical safety assessment

Additional information

No experimental data evaluating the toxicity of isooctadecanoic acid, mono- and diester with glycerol (CAS No. 97358-80-0) to algae are available. Therefore, toxicity data from a structurally related category member (Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri-, CAS No. 91052-28-7) are used as read-across in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. Both are UVCB substances, formed from the esterification of long-chain fatty acids (C14-18 and C16-18 unsaturated and C18 iso for CAS No. 91052-28-7 and CAS No. 97358-80-0, respectively) and glycerol. They are predominantly monoesters. Furthermore, both substances are insoluble in water (water solubility 0.1 mg/L and < 0.05 mg/L for target and source substance, respectively) and have log Kow values > 4. They are expected thus to show similar behaviour in the water phase. The acute tests conducted with these two substances on Daphnia magna (Schlechtriem (2012); Salinas (2013)) showed no immobilization up to a nominal loading rate of 100 mg/L (WAF). Therefore, the EL50 (48 h) values were determined to be > 100 mg/L (nominal, loading rate). There results indicate that indeed, due to their structural and physico-chemical similarities, isooctadecanoic acid, mono- and diester with glycerol and Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri- are expected to exhibit a comparable toxicity profile. Based on the above information, the use of Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri- as read-across substance is considered justified.

 

One study evaluating the toxicity of Glycerides, C14-18 and C16-18 unsaturated, mono-, di- and tri- (CAS No. 91052-28-7) to algae is available (Salinas, 2013). This test was conducted according to OECD Guideline 201, under GLP conditions. Desmodesmus subspicatus was exposed for 72 hours to the test substance at test concentrations of 3.2, 10, 32, 100 and 320 mg/L (nominal, loading rate). Chlorophyll-a fluorescence (pulsed excitation with light flashes having a wavelength of 430 nm) was the measured test parameter. Nevertheless, cell density was also determined in order to derive the linear correlation between both parameters. After 72 hours of exposure, effects on algal growth rate were observed at concentrations of 100 mg/L and 320 mg/L, leading to an ErL10 of 172 mg/L and a NOELR of 32 mg/L (nominal, loading rate). The ErL50 was determined to be > 320 mg/L (nominal, loading rate). The reported effects are well above the water solubility of the substance (water solubility < 0.05 mg/L) and therefore, they could be caused by physical interference or adsorption between algae and the test substance. Nevertheless, stock solutions were reported to be colourless and clear, and therefore, effects due to toxicity cannot be discarded.

 

Based on the results obtained for the structurally related analogue (in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5), isooctadecanoic acid, mono- and diester with glycerol could exhibit low toxicity to algae.

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