Reaction mass of 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane

Short-term toxicity to aquatic invertebrates

Description of key information

48-hour EC₅₀: >2.9 µg/L (measured concentration) for the effects of D5 on mobility of Daphnia magna, read-across to Constituent 1, Vi5-D5. No effects were observed up to the water solubility limit of the test substance.

48-h LL₅₀: 272 mg/l loading rate (WAFs) for the effects of Vi4-D4 on mobility of the marine copepod Acartia tonsa. No effects were observed up to the water solubility limit of the test substance.

Additional information

There are no reliable short-term invertebrate toxicity data available for the registration substance as a whole, therefore good quality data from Constituent 2 and read-across from a structural analogue of Constituent 1 have been read across.

The following data have been read across from decamethylcyclopentasiloxane (D5, 541-02-6) for Constituent 1, Vi5-D5:

A 48-hour EC₅₀ value of >2.9 µg/L (measured concentration) has been determined for the effects of D5 on mobility of Daphnia magna, in accordance with OECD guideline 202. A NOEC of ≥2.9 µg/L has been determined in the same test (Springborn Smithers 2002). In view of the test media preparation method of preparing a saturated stock solution in acetone, and the flow-through exposure regime, it is likely that the test organisms were exposed predominantly to the highest achievable concentrations of the parent substance, and therefore there were no effects observed up to the water solubility limit of the test substance.

The following data are available for 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4, CAS 2554-06-5):

A 48-h LL₅₀ value of 272 mg/l and NOELR of 100 mg/l loading rate (WAFs) (not possible to extrapolate to measured concentrations) have been determined for the effects of Vi4-D4 on mobility of the marine copepod Acartia tonsa, in accordance with ISO/FDIS 14669 a PARCOM ring test protocol (TNO, 2003). The LL₅₀ is above the water solubility limit of the substance (0.0073 – 0.0088 mg/l at 23°C). For monoconstituent substances it would not normally be appropriate to test at concentrations above the solubility limit. However, the results as reported do provide strong evidence of the absence of toxicity at the solubility limit of the substance following short-term exposures.

In view of the hydrolysis half-life of the test substance, the method of preparation of the test solution (20 hours stirring at approximately pH 8) and the static exposure regime, it is likely that the test organisms were exposed to a mixture of parent substance and hydrolysis product.

 

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