Sorbitan tristearate

Long-term toxicity to aquatic invertebrates

Description of key information

NOELR (21d) ≥ 16 mg/L for Daphnia magna (OECD 211); read-across

Additional information

No studies are available on the toxicity of Sorbitan tristearate (CAS 26658-19-5) to aquatic invertebrates. The assessment was, therefore, based on a study conducted with the structurally similar category member Sorbitan stearate (CAS No. 1338-41-6). This read across approach is in accordance with Regulation (EC) No 1907/2006, Annex XI, 1.5. Grouping of substance and read across approach. Sorbitan tristearate and Sorbitan stearate are both Sorbitan esters of saturated C18 fatty acids. Since the Sorbitan stearate mainly consists of monoesters, it can be considered a worst case read-across to Sorbitan tristearate, which is expected to be less bioavailable due to its molecular size (MW 879-982). 

The key study conducted with Sorbitan stearate (CAS 1338-41-6) was performed according to OECD guideline 211 and GLP (Ministry of the Environment, Government of Japan, 2006). The test organism Daphnia magna was exposed to the test substance in a semi-static system for 21 days, at nominal concentrations of 5, 16, 50, 160 and 500 mg/L. The test concentrations 5 and 16 mg/L were prepared using tetrahydrofuran as pre-solvent. Before the test, the solvent was removed and the solution was filtered. The higher concentrations were prepared without solvent as water accommodated fractions (WAF). Since a solvent was used, the lower concentrations are not actual loading rates and these test concentrations cannot be evaluated as WAF. No inhibition of reproduction was observed during the test, in fact, the number of juveniles produced at 5 and 16 mg/L was higher than in the control. At the three higher concentrations, 100% mortality of the parental daphnia occurred, and reproduction could not be evaluated. The reported measured values for the three highest concentrations (4.65, 11.9, 17.1 mg/L) were significantly above the water solubility of the substance. Therefore, it can be assumed that undissolved test material was present and probably caused the mortality observed at the higher concentrations. Due to the methodological deficiencies in this test, the reported NOEC and EC50 need to be taken with caution. Nevertheless, at nominal concentration of 16 mg/L the test solution was reported to be clear and colourless during the test period, and no adverse effects occurred. The corresponding measured concentration 1.44 mg/L is clearly above the water solubility of Sorbitan stearate (0.01 mg/L) and was probably only attained due to the use of solvent. Therefore, 16 mg/L is used as NOELR. Sorbitan stearate is thus not expected to have adverse effects on the reproduction of daphnia magna up to the limit of water solubility.