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Long-term toxicity to aquatic invertebrates

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Description of key information

Long-term toxicity to invertebrates: 21-d NOEC 0.0079 mg/l (guideline EPA OTS 797.1330 (Daphnid Chronic Toxicity Test)), read-across from an analogous/structurally related substance, Octamethylcyclotetrasiloxane (D4, CAS 556-67-2).  

Key value for chemical safety assessment

Additional information

There are no reliable long-term invertebrate toxicity data available for the registration substance, therefore good quality data for an appropriate structural analogue, octamethylcyclotetrasiloxane (D4, CAS: 556-67-2), have been read across.

 

A 21-d NOEC of 0.0079 mg/l has been determined for the effects of octamethylcyclotetrasiloxane (D4, CAS: 556-67-2) on survival and reproduction of Daphnia magna. A 21-d EC50 of > 0.015 mg/l has been determined in the same test for effects on mortality.

Because D4 has a higher water solubility than the registration substance (0.056 mg/l and 0.0073 – 0.0088 mg/l respectively) and the long-term no observed effect concentration (0.0079 mg/l) for D4 is very close to the limit of water solubility for the registration substance, it is not possible to conclude with confidence whether the NOECs from the study with D4 will be above or below the limit of solubility for the registration substance. Therefore, toxicity may or may not be expressed in long-term studies for the registration substance. This is key for concluding on classification and labelling; therefore, testing proposals are put forward.

 

The data above are supported by read-across evidence relevant to the impurities. The registration substance has an average purity of 80% Vi4-D4, with <15% 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane Vi5-D5 (CAS 17704-22-2; Impurity 1) and <10% 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane Vi3-D3 (CAS 3901-77-7; Impurity 2) present as impurities. After due consideration of the properties, the presence of these impurities is not expected to affect the overall hazard profile of the substance. Read-across studies are in place as supporting studies, to consider the properties of the impurities. Data for Vi5-D5 are read-across from decamethylcyclopentasiloxane D5 (CAS 541-02-6). These siloxanes have similar properties with regard to aquatic ecotoxicity.  Further information is given in a supporting report (PFA, 2017) attached in Section 13 of the IUCLID 6 dossier.

A reliable long-term invertebrate study is available for the siloxane D5 (CAS 541-02-6) and is read-across to Impurity 1 (Vi5-D5). This study (21-d reproduction test withDaphnia magna) gave a result 21-d NOEC ≥15 µg/l. Effects were not seen within the limit of solubility in test media.

No reliable long-term invertebrate study is available to read-across to Impurity 2. Effects are not anticipated at the limit of solubility and the available data for the main data set are conservative in respect of Impurity 2, which has a much shorter hydrolytic half-life and lower log Kow. The chemical safety assessment is therefore not sensitive to this data gap.