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Short-term toxicity to aquatic invertebrates

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Description of key information

48h-EC50 > 0.02 mg/L (measured initial concentration) for Daphnia magna (OECD 202)
48h-EC50 and EL50 > 100 mg/L (nominal concentration and loading rate) for Daphnia magna (EU Method C.2)
48h-EL50 > 1000 mg/L (nominal loading rate) for Acartia tonsa (ISO Proposal)

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Additional information

No experimental data evaluating the acute toxicity of Fatty acids, C16-C18, methyl esters (CAS No. 85586-21-6) to aquatic invertebrates are available. Therefore, toxicity data from structurally similar analogue substances, Fatty acids, C16-18 and C18 unsaturated, methyl esters (CAS No. 67762-38-3), Fatty acids C16-18 unstd., methyl esters (CAS No. 67762-26-9) and tetradecanoic acid, methyl ester (CAS No. 124-10-7) are used as read-across in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. All four substances are fatty acids esterified with methanol, containing fatty acid C-chain lengths of C14 (CAS No. 124-10-7) and C16-18 (saturated and unsaturated) (CAS No. 67762-38-3, 67762-26-9 and the target substance, CAS No. 85586-21-6) respectively. The C14 substance (CAS No. 124-10-7) was chosen as read-across substance as monoconstituent representative of medium-to-high fatty acid chain lengths within the category. This substance, even when comparable to the target substance, has a shorter fatty acid C-chain length and due to this fact, the molecular size and weight will be lower than those of CAS No. 85586-21-6, and can be expected to have also a slightly higher solubility in water. For those reasons, tetradecanoic acid, methyl ester (CAS No. 124-10-7) can be expected to be more bioavailable to aquatic organisms and can be regarded as a worst-case read-across for Fatty acids, C16-18, Me esters (CAS No. 85586-21-6).

The log Pow (> 5 for all substances) and water solubility values (0.05 mg/L for CAS No. 124-10-7, < 0.05 mg/L for CAS No. 67762-38-3 and < 1 mg/L for CAS No. 67762-26-9 and CAS No. 85586-21-6) of these four substances indicate that, besides the structural similarities that will lead to similar toxicity profiles, a comparable behaviour in water for all of them can be expected. Based on this information, it is justified to use the toxicity data from the analogues as read-across for Fatty acids, C16-C18, methyl esters, according to Regulation (EC) No. 1907/2006, Annex XI, 1.5.

One study evaluating the acute toxicity of tetradecanoic acid, methyl ester (CAS No. 124-10-7) to aquatic invertebrates is available (Migchielsen, 2010). This test was performed according to OECD Guideline 202, under GLP conditions. Daphnia magna was exposed to the test substance for 48 h within a semi-static water regime (medium renewal at 24 h) at 21 ± 1°C. Analytical determinations of test concentrations in the solution were performed during the test. Due to the insolubility of the substance in water (water solubility < 0.05 mg/L), the test substance concentration could only be detected after the 24-h water renewal, being 0.02 mg/L. After 48 hours, no significant effects were observed at the concentration tested and therefore, the 48h-EC50 was determined to be > 100 mg/L (nominal concentrations) and > 0.02 mg/L (measured initial concentration).

The test available for Fatty acids C16-18 unstd., methyl esters (CAS No. 67762-26-9) was performed according to EU Method C.2, under GLP conditions (Kuch, 1996). In this static test, Daphnia magna was exposed to the test substance for 48 h in two solutions: one in which the test substance was directly added to the medium and a Water Accommodated Fraction (WAF). Effects on mobility were recorded every 24 hours. No significant immobilization was observed in any of the treatment groups and therefore the 48-EC50 and EL50 were > 100 mg/L (nominal).

Additionally, a marine test was conducted with Fatty acids, C16-18 and C18 unsaturated, methyl esters (CAS No. 67762-38-3) according to the ISO Proposal: Determination of acute lethal toxicity to marine adult copepods (Acartia tonsa DANA), under GLP conditions (Hudson, 1998). Acartia tonsa was exposed for 48 h to the test substance within a static water regime. After the exposure period, the 48h-EL50 was determined to be > 1000 mg/L (nominal, loading rate).

Based on the results obtained for structurally related analogue substances (according to Regulation (EC) No. 1907/2006, Annex XI, 1.5), Fatty acids, C16-C18, methyl esters (CAS No. 85586-21-6) is not expected to show acute toxicity to aquatic invertebrate species up to the limit of its water solubility (< 1 mg/L).