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Toxicity to aquatic algae and cyanobacteria

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Description of key information

EL50 (72 h) = 17.89 mg/L (nominal, WAF, based on growth rate)
NOELR (72 h) ≥ 10 mg/L (nominal, WAF, based on growth rate)

Key value for chemical safety assessment

Additional information

No studies investigating the short-term toxicity to algae and cyanobacteria of sorbitan C16-18 (even numbered) fatty acid esters, ethoxylated (1-6.5 moles ethoxylated) are available. Therefore, in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5 a read across was conducted to the structurally related source substances sorbitan stearate – C18 (CAS 1338-41-6), sorbitan laurate – C12 (CAS 1338-39-2) and sorbitan monolaurate ethoxylated (CAS 9005-64-5).

The toxicity of sorbitan stearate (CAS 1338-41-6) was tested on algae according to the Circular on Test Methods of New Chemical Substances (Japan), Alga Growth Inhibition test and GLP (MoE, 2005). The test organism Pseudokirchneriella subcapitata was exposed to the test substance in a static system for 72 h, at the nominal test concentrations of 100, 180, 320, 560 and 1000 mg/L. The test solutions were prepared as water accommodated fractions (WAF), but the reported measured concentrations, far above the solubility limit of this substance, indicate that undissolved material was present. Significant inhibition was only observed at the concentration of 1000 mg/L. NOELR and EL50 values of 560 mg/L and > 1000 mg/L (nominal, WAF), respectively, were determined. It is, however, very likely that the effect at the highest tested concentration was due to the turbidity of the test solution, caused by the undissolved test material. The results are also reported in measured concentrations as NOEC = 100 mg/L and EC50 > 122 mg/L. However, since these concentrations are far above the water solubility of the test substance and because the substance is an UVCB, the assessment was based on the nominal concentrations.

A further study is available on the short-term toxicity of sorbitan laurate (CAS 1338-39-2) to algae, performed according to the ISO 10253, EPA/600/4-85/013 and GLP (Hudson, 1999). The test organism Skeletonema costatum was exposed to the test substance in a static system for 72 h, at the nominal test concentrations of 3.2, 10, 32, 100 and 320 mg/L. The test solutions were prepared as water accommodated fractions (WAF). At the two lowest concentrations algal growth was stimulated by the test substance, but at the higher concentrations no growth was observed. The lack of a dose response relation rather indicates a physical effect caused by undissolved test material than a systemic toxic effect. An EL50 of 17.89 mg/L (nominal, WAF) is reported. A NOEC is not reported, but as no adverse effect occurred up to 10 mg/L, the NOEC was set to 10 mg/L (nominal, WAF).

A study is available on the short-term toxicity of sorbitan monolaurate, ethoxylated (CAS 9005-64-5) performed according to OECD guideline 201 and GLP (Wenzel, 2012). The test organism Pseudokirchneriella subcapitata was exposed to the test substance in a static system for 72 h, at nominal loading rates between 1 and 100 mg/L. The test solutions were prepared as water accommodated fractions (WAF). ErL50 and ErL10 values of 58.84 mg/L and 19.05 mg/L, respectively, were derived.

Based on the results from the above mentioned structurally related read-across substances (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5), which are characterized by a similar ecotoxicological profile, it can be concluded that the same result on aquatic algae and cyanobacteria are expected when testing sorbitan C16-18 (even numbered) fatty acid esters, ethoxylated (1-6.5 moles ethoxylated).