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Ecotoxicological information

Long-term toxicity to fish

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Link to relevant study record(s)

Description of key information

90-day NOEC >0.014 mg/l: effects of D5 on hatching, survival and growth of Oncorhynchus mykiss, read-across to Constituent 1, Vi5-D5. No effects were observed up to the water solubility limit of the test substance.

93-day NOEC ≥0.0044 mg/l: effects of D4 on embryo viability, hatching success, larval survival and growth of early life stages of Oncorhynchus mykiss, read across to Constituent 2, Vi4-D4.

Key value for chemical safety assessment

Additional information

No long-term aquatic toxicity data are available for the registration substance. Although this is not a requirement at this annex level, long-term tests should be considered because the substance is poorly water soluble. If only short-term data are provided, a “safety net” classification Category Chronic 4 could apply because the substance is poorly soluble and shows no acute toxicity up to the limit of water solubility, is not rapidly degradable and has a log Kow >4. Long-term aquatic toxicity studies have therefore been included.

There are no reliable long-term fish toxicity data available for Constituent 1 of the registration substance, 2,4,6,8,10 -pentamethyl-2,4,6,8,10 -pentavinyltetrasiloxane (Vi5-D5, CAS 17704-22-2), therefore data are read across from decamethylcyclopentasiloxane (D5, CAS 541-02-6). A 90-day NOEC of >0.014 mg/l has been determined for the effects of D5 on hatching, survival and growth of Oncorhynchus mykiss. Effects were not seen within the limit of solubility in test media.

There are no reliable long-term fish toxicity data available for Constituent 2 of the registration substance, 2,4,6,8-tetramethyl-2,4,6,8-tetravinyltetrasiloxane (Vi4-D4, CAS 2554 -06 -5), therefore good quality data for an appropriate structural analogue, octamethylcyclotetrasiloxane (D4, CAS 556-67-2), have been read across. A 93-day NOEC of ≥0.0044 mg/l has been determined for the effects of D4 on embryo viability, hatching success, larval survival and growth of early life stages of Oncorhynchus mykiss.

Because D4 has a higher water solubility than Vi4-D4 (0.056 mg/l and 0.0073 – 0.0088 mg/l respectively) and the long-term no observed effect concentration (≥0.0044 mg/l) for D4 is very close to the limit of water solubility of Vi4-D4, 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 of Vi4-D4. Therefore, toxicity may or may not be expressed in long-term studies with Vi4-D4. This is key for concluding on classification and labelling; therefore, testing proposals have been put forward for Vi4-D4 as a monoconstituent substance. These studies can also be used for the registration substance.

Refer to Section 6 Ecotoxicological Information for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.