2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane

Endpoint summary

Additional information

The following data are available describing the short-term toxicity of the registration substance to marine organisms:

• Fish: A 96 hour LL₅₀ value of >1000 mg/l and NOELR of 560 mg/l have been determined for effects on mortality of Cyprinodon variegatus.
• Invertebrates: A 48 hour LL₅₀ value of 272 mg/l and NOELR of 100 mg/l have been determined for effects on mobility of Acartia tonsa.
• Algae: A 70.5 hour EL₅₀ of >988 mg/l and NOELR of ≥988 mg/l have been determined for effects on growth of Skeletonema costatum.

These values are all well above the water solubility limit of Vi4-D4 (0.0073 – 0.0088 mg/l at 23°C). However, the results as reported do provide strong evidence of the absence of short-term toxicity at the solubility limit of the substance.

Reliable long-term invertebrate toxicity data are available for the registration substance, 2,4,6,8-tetramethyl-2,4,6,8-tetravinyltetrasiloxane (Vi4-D4, CAS 2554 -06-5). The relevant long-term value is:

• Long-term invertebrates: A 21 day NOEC value of ≥0.00378 mg/l based on geometric mean measured concentrations has been determined for the effects of the registration substance on survival and reproduction of Daphnia magna.

Reliable long-term toxicity to fish data are available for the registration substance, 2,4,6,8-tetramethyl-2,4,6,8-tetravinyltetrasiloxane (Vi4-D4, CAS 2554 -06-5). The relevant long-term value is:

• Long-term fish: A 28 day post hatch NOEC value of ≥0.036 µg/l based on geometric mean measured concentrations has been determined for the effects of Vi4-D4 on embryo viability, hatching success, larval survival and growth of fathead minnow (Pimephales promelas).

An activated sludge respiration inhibition 3 hour EC₅₀ value of >1000 mg/l and NOEC value of ≥1000 mg/l (nominal) were determined in a reliable study.  

No effects were observed in any of the aquatic toxicity tests, indicating that the registration substance is not toxic at its limit of water solubility.

Data for short-term toxicity to fish, invertebrates and algae have been read-across from trimethox(vinyl)silane (CAS 2768-02-7), which also contains a vinyl side chain. L(E)C₅₀ values are reported in the range of >89 -191 mg/l, indicating that the side chain is not contributing significant short-term toxicity to the substance. It is therefore also unlikely to contribute significant toxicity to this substance.

Data are also read across from analogous siloxanes hexamethyltrisiloxane D3 (CAS 541-05-9) and decamethylcyclopentasiloxane D5 (CAS 541-02-6) to assess the toxicity of the impurities present in the registration substance. The registration substance has an average purity of >70% Vi4-D4, with <20% 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. The available data with D3 and D5 indicate that the substances are not toxic at their limit of solubility. The presence of Vi3-D3 and Vi5-D5 impurities are therefore not expected to affect the overall hazard profile of the substance.

Refer to IUCLID Section 6 endpoint summary (CSR Section 7.0) for further discussion of the approach to chemical safety assessment and justification for read across.