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Short-term toxicity to aquatic invertebrates

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Description of key information

EL50 (48h) > 1 < 10 mg/L for immobilisation of Daphnia magna  (OECD 202). A statistical analysis of the raw data resulted in a 48-h EL50 value of 5.05 mg/L.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
5.05 mg/L

Additional information

One study investigating the short-term toxicity to aquatic invertebrates of 1,2,3-Propanetriol, homopolymer, diisooctadecanoate (CAS 63705-03-3) is available. The study was performed according to OECD guideline 202 but not under GLP conditions since the study was primarily intended to be a pre-test to determine the test concentrations of the long-term toxicity test with Daphnia magna (see chapter 6.1.4). The nominal test concentration of 100 mg/L was prepared by weighing the test item and mixing it with the test medium. The mixture was then stirred at room temperature for 24 hours. After stirring, undissolved parts of the mixture were separated by filtration through a nitrocellulose membrane filter (0.45 µm). The filtrate was the water accommodated fraction (WAF) used for the exposure. The highest test concentration of 100 mg/L was used to prepare the lower test concentrations (0.1, 1.0 and 10 mg/L) by sequential dilution. After a test duration of 48 h 45% immobilization was observed in the 1 mg/L and 65% in the 10 mg/L treatment. Thus, the 48-h EL50 value is determined to be between 1 and 10 mg/L. A statistical analysis performed by the owner company revealed a 48-h EL50 value of 5.05 mg/L based on the raw data given in the study.

The observed EC50 value is much higher than the solubility of the UVCB substance in water (< 0.15 mg/L). Therefore, in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5 read across to the structurally similar analogue substances isooctadecanoic acid, mono- and diester with glycerol (CAS No. 97358-80-0) and Glycerides, C16-18 and C18-unsatd. (CAS 67701-30-8) was conducted in order to verify if metabolites of the ester components may have been caused the observed toxicity. 1,2,3-Propanetriol, homopolymer, diisooctadecanoate (CAS 63705-03-3) is characterized by mono-, di- and tri-esters of glycerol, diglycerol and triglycerol esterified with C18iso fatty acid. The read across substance isooctadecanoic acid, mono- and diester with glycerol (CAS 97358-80-0) is a mono-, di- and tri-ester of glycerol and C18iso fatty acid. Thus, this source substance is structurally very similar to the target substance. In addition, isooctadecanoic acid, mono- and diester with glycerol is a worst case read across, as due to the higher water solubility (0.1 mg/L at 20 °C) the bioavailability of this source substance is expected to be higher as for the target substance (water solubility < 0.15 mg/L at 20 °C). The second read-across substance Glycerides, C16-18 and C18-unsatd. (CAS 67701-30-8) is characterized as a triester of glycerol and fatty acids of C16-18 and C18 uns. covering the more complex triester-structure of 1,2,3-Propanetriol, homopolymer, diisooctadecanoate (CAS 63705-03-3). Additionally, for the endpoints short-term toxicity to fish and toxicity to algae 1,2,3-Propanetriol, homopolymer, diisooctadecanoate (CAS 63705-03-3) and the source substance Glycerides, C16-18 and C18-unsatd. (CAS 67701-30-8) show a consistent pattern of results. Therefore, a similar ecotoxicological profile is expected for both substances. Based on the structural similarity both source substances can be used for a reliable assessment of the aquatic toxicity of the target substance.

The study with the read-across substance isooctadecanoic acid, mono- and diester with glycerol (CAS 97358-80-0) was performed according to OECD 202 under GLP conditions (Schlechtriem, 2012). Daphnia magna was exposed to the test substance for 48 hours within a semi-static water regime. After the exposure period, no immobilization or other sub-lethal effects were observed and therefore the EL50 (48 h) was determined to be > 100 mg/L (nominal loading rate).

The supporting study with the read-across substance Glycerides, C16-18 and C18-unsatd. (CAS 67701-30-8) was conducted according to EU Method C.2 under GLP conditions (Kück, 1995). Daphnia magna was exposed to the test substance for 48 hours within a static exposure regime. Two different test solutions were prepared, for the first solution the test substance was directly weighed into the vessel with ultrasonicated for 5 min and for the second solution the test substance was stirred and the undissolved test substance was separated by filtration. In the first solution black particles and turbidity was observed. Nevertheless, in both solutions no effects up to the water solubility were observed (first solution: EC50 (48 h) > 100 mg/L (nominal); second solution: EC50 (48 h) > 0.01 mg/L (meas. initial)).

Based on the results from the structurally related read-across substances (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5), it can be concluded that the ester components most probably did not cause the toxicity observed in the acute toxicity test with the target substance. It is assumed that soluble metabolites of the isooctadecanoic acid component are responsible for the mortality of the parental daphnids.