Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

Terrestrial testing is not an Annex VIII requirement for Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9). However, the low water solubility, high log Kow and high log Koc of the substance indicate that it will adsorb to organic matter and partition to sludges in a waste water treatment plant. No effects were observed in the short-term aquatic toxicity tests. As the substance is poorly water soluble and the aquatic data available are based on WAFs, it may be more appropriate to use terrestrial data to assess the potential toxicity of the substance in the environment.

No terrestrial toxicity data are available for the registration substance; a category approach is applied to this endpoint and is detailed in the Siloxane Category report (PFA, 2017at).

There is a limited amount of terrestrial toxicity data available with siloxanes. An integrated testing strategy for the category is proposed. In view of the high potential to adsorb to soil for siloxane substances, and the lack of terrestrial toxicity testing across the Category, it is concluded that further testing is required.

Screening Assessment and Testing Strategy for Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9)

The registration substance falls within soil hazard category 3 as defined in REACH R.7; high absorption (log Kow >5) but no indication that the substance is very toxic to aquatic organisms. As discussed in Section 6.0, for substances with a log Kow of ~6 or above, aquatic toxicity is not expected because the very limited aqueous solubility prevents toxic concentrations being achieved. Aquatic toxicity data show no effects at loading rates that are above the limit of water solubility of the substance. A true PNEC cannot be calculated from the aquatic test data because the EL50 values that have been determined are limit values and loading rate values should not be used for PNEC derivation. It is therefore not possible to conduct the screening assessment for terrestrial testing by calculating a PNECsoil using the equilibrium partitioning approach.

Terrestrial tests with the registration substance are required by ECHA final decision TPE-D-2114497761-36-01/F. OECD TG 222 earthworm reproduction, OECD TG 208 seedling emergence and OECD TG 216 soil microorganisms tests are currently ongoing.

The substance dataset and risk assessment will be updated once results of the three terrestrial studies are available and the studies are finalised. An update is planned to be completed within three months from when the last final report is received. The final reports are expected in March 2021 for the OECD TG 222 study, and January 2021 for the OECD TG 208 study. Please see letters from the OECD TG 222 and OECD TG 208 testing laboratories, attached in IUCLID Section 6.3.1 and 6.3.3 placeholder EPSRs, respectively, for further details.

The OECD TG 216 soil microorganisms test has been conducted and the draft study report is available and has been written up in the dossier, although it may be subject to change depending on the final report.

 

Until these data become available, PNECsoil has been derived based on data read across from decamethylcyclopentasiloxane (D5, CAS 541-02-6) in order to perform risk characterisation.

Read-across justification

Read-across from decamethylcyclopentasiloxane (D5, CAS: 541-02-6) to Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9):

In the interim period, before the data with the registration substance become available, data can be read-across from D5 (CAS 541-02-6) for toxicity to soil macroorganisms except arthropods, toxicity to terrestrial arthropods and toxicity to terrestrial plants. The data are considered to be suitable for deriving an interim PNECsoil for the registration substance.

The registration substance, Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9), and the surrogate substance decamethylcyclopentasiloxane (D5, CAS 541-02-6) are both members of the siloxanes category. D5 is a cyclic siloxane with 5 silicon atoms with methyl branches and alternated by oxygen. The registration substance is a multi-constituent substance containing two main constituents 3,3-diphenylhexamethyltrisiloxane (55-70%) and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (15-25%). The main constituent has three silicon atoms with 2 phenyl groups and 6 methyl groups. The second constituent has 4 silicon atoms, with 4 phenyl groups and 6 methyl groups. Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9) and D5 have similar physicochemical properties: high molecular weight (360.68-558.98 g/mol and 370 g/mol respectively), low water solubility (2.8E-05 mg/L for Constituent 1, 1.5E-10 mg/L for Constituent 2 and 1.7E-03 mg/L for D5), high log Kow (9.0 and 8.0 respectively) and high log Koc (6.0 and 5.17-5.34, respectively). Both substances have negligible biodegradability and hydrolysis rates. A comparison of the key physicochemical properties is presented in the table in Section 6.0,

• A 28-day LC50 value of >4074 mg/kg dry weight and a 56-day NOEC of ≥4074 mg/kg dry weight have been determined for the effects of D5 on mortality and reproduction and growth respectively of the earthworm, Eisenia andrei.

• A 28-day LC50 value of 813 mg/kg dry weight and a 28-day IC50 value of 767 mg/kg dry weight have been determined for the effects of the D5 on mortality and reproduction of the springtail, Folsomia candida. A NOEC of 377 mg/kg dry weight has been determined by the reviewer on the basis of a visual examination of the data for both mortality and reproduction.

• A 14 day IC50value of 209 mg/kg dry weight has been determined for the effects of the test substance on root dry mass of Barley, Hordeum vulgare. IC50/EC50 values for effects on seedling emergence, root and shoot length and shoot dry mass determined in the same test were ≥248 mg/kg dry weight. 14 Day EC50 values of >4054 mg/kg dry weight have been determined for the effects of the test substance on seedling emergence, root and shoot length and root and shoot dry mass of Red Clover, Trifolium pratense. NOECs were not determined in the tests.

The studies are considered to be non-standard; they have been conducted by spiking surrogate biosolids mixed into natural soil rather than by direct spiking of soil. The registered substance and the surrogate substance share similar physicochemical properties but are not close structural analogues (linear and cyclic siloxanes).

Read-across of the terrestrial toxicity data for D5 to Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9) is considered to be suitable to derive an interim hazard and risk assessment under REACH until the data with the registration substance are available.