Registration Dossier
Registration Dossier
Diss Factsheets
Use of this information is subject to copyright laws and may require the permission of the owner of the information, as described in the ECHA Legal Notice.
EC number: 220-099-6 | CAS number: 2627-95-4
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data

Ecotoxicological Summary
Administrative data
Hazard for aquatic organisms
Freshwater
- Hazard assessment conclusion:
- no hazard identified
Marine water
- Hazard assessment conclusion:
- no hazard identified
STP
- Hazard assessment conclusion:
- no hazard identified
Sediment (freshwater)
- Hazard assessment conclusion:
- PNEC sediment (freshwater)
- PNEC value:
- 8.9 mg/kg sediment dw
- Assessment factor:
- 10
- Extrapolation method:
- assessment factor
Sediment (marine water)
- Hazard assessment conclusion:
- PNEC sediment (marine water)
- PNEC value:
- 0.89 mg/kg sediment dw
- Assessment factor:
- 100
- Extrapolation method:
- assessment factor
Hazard for air
Air
- Hazard assessment conclusion:
- no hazard identified
Hazard for terrestrial organisms
Soil
- Hazard assessment conclusion:
- no hazard identified
Hazard for predators
Secondary poisoning
- Hazard assessment conclusion:
- PNEC oral
- PNEC value:
- 14.44 mg/kg food
- Assessment factor:
- 90
Additional information
The hydrolysis half-life of 1,1,3,3-tetramethyl-1,3-divinyldisiloxane (CAS 2627-95-4, Vi2-L2) is 3.7 h at pH 5, 5.8 days at pH 7 and 2.6 h at pH 9 and 25°C. The water solubility of the substance is low (0.21 mg/l) and the log Kow is high (5.4).
REACH Guidance (ECHA 2017, R.7b) indicates that the parent substance should be tested if the DT50 is greater than 3 days. In addition, REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT50 is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. TGD and REACH guidance (EC 2003) and R.16 (2016) also suggest that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Due to the slow hydrolysis half-life, the environmental Chemical Safety Assessment is therefore based on the properties of the parent substance.
Due to the low water solubility and high log Kow, aquatic organisms are likely to be exposed to low dissolved concentrations of the substance in the environment.
In the sediment and soil compartments adsorption to particulate and organic matter will be high.
It is therefore likely that, under the flow-through exposure conditions of the fish study that the test organisms will have predominantly been exposed to the registration substance. In the semi-static long-term invertebrate study and the static algal test it is likely that exposure will have been predominantly to the registration substance and a small proportion of its hydrolysis products. The test substance is volatile but measures were taken to maintain exposure concentrations by conducting the key fish test under flow-through conditions, the chronic invertebrate test under semi-static conditions and the algal test under sealed conditions.
READ-ACROSS JUSTIFICATION
In order to reduce testing read-across is proposed to fulfil up to REACH Annex IX requirements for the registered substance from substances that have similar structure and physicochemical properties. Risk characterisation for all substances needs sediment to be assessed and therefore a reliable PNEC is needed regardless of Annex requirements.
The registration substance Vi2-L2 (CAS 2627-95-4) and the substances used as surrogates are members of the Reconsile Siloxane Category. Substances in this category tend to have slow hydrolysis rates, low water solubility, high log Kow, high adsorption coefficients and slow degradation in the sediment compartment.
Additional information is given in a supporting report (PFA 2017) attached in Section 13 of the IUCLID 6 dossier. The Siloxane Category report (PFA, 2017) addresses the Assessment Elements of the RAAF and, in addition to describing the siloxanes category, forms the RAAF justification report.
In the following paragraphs the category read-across approach for the registered substance is outlined, taking into account structure and physicochemical properties.
Read-across from hexamethyldisiloxane (L2) and octamethyltrisiloxane (L3) to 1,1,3,3-tetramethyl-1,3-divinyldisiloxane (CAS 2627-95-4, Vi2-L2):
The registration substance, 1,1,3,3-tetramethyl-1,3-divinyldisiloxane (CAS 2627-95-4, Vi2 -L2), and the source substances hexamethyldisiloxane (L2, CAS 107-46-0) and octamethyltrisiloxane (L3, CAS 107-51-7) are members of the Siloxane Category. L2 and L3 are linear siloxanes with two silicon atoms and one oxygen atom, and three silicon and two oxygen atoms, respectively. Each of the silicon atoms are fully substituted with methyl groups. Vi2-L2 is a linear siloxane with two silicon atoms and one oxygen atom. One vinyl and two methyl groups are attached to each silicon atom with a total of four methyl and two vinyl groups. Refer to Section 1 for more structural information on the registration substance including diagrams.
Terrestrial toxicity studies with siloxanes such as Vi2-L2, L2 and L3 are technically difficult to conduct due to their high volatilisation potential (high Henry’s Law Constant and low octanol-air partition coefficient) and the potential for degradation in soil. Soil testing according to guideline methods does not allow for a renewal of the substrate and hence re-application of test substance. Therefore, there is potential for the organisms to not be exposed to the test material for a sufficiently long period of time for effects to be expressed, as well as the difficulty of quantifying actual exposure concentrations. OECD TG 222 acknowledges that the test method may not be applicable to substance for which the air-soil partition coefficient is greater than one, or to substance with vapour pressure exceeding 300 Pa at 25°C. Terrestrial toxicity testing with L2 and L3 has shown this to be the case (see discussion in IUCLID Section 6.3 and CSR Section 7.2). L2 and L3 meet both of these criteria (for L2, Kair-soil = 3.3 at 20°C (temperature for terrestrial testing), VP 5500 Pa at 25°C; for L3, Kair-soil = 1.3 at 20°C, VP 530 Pa at 25°C). The air-soil partition coefficient for Vi2-L2 is 3.3 at 20°C and the vapour pressure is 1700 Pa at 25°C.
The physical-chemical properties of L3 and L2 are generally consistent and similar to those of Vi2-L2, meaning this read across to Vi2-L2 is a robust interpolation. Homogeneous hydrolysis rates are comparable. The substances have similar molecular weight, relatively low water solubility and high log Kow. See table 7.0.1 for relevant values. All three substances have negligible biodegradability.
Table 7.0.1 Relevant Physicochemical Properties of the Registration and Proposed Test Substances
Substance |
Vi2-L2 |
L2 |
L3 |
Vapour Pressure (Pa) |
1700 |
5500 |
530 |
Log Koc |
3.2 |
3.0 |
4.3 |
Hydrolysis (hours) (pH7, 20-25˚C) |
140 |
116 |
329 |
Molecular Weight |
186.40 |
162.38 |
236.54 |
Water Solubility (mg/l) |
0.207 |
0.93 |
0.034 |
Log Kow |
5.4 |
5.06 |
6.60 |
L2 and L3 data are used for read-across to the sediment compartment. In addition, soil microorganisms tests with L2 and L3, and a terrestrial stability test with L3 under OECD 222 conditions, have been read across.
Conclusion on classification
The substance has reliable short-term E(L)C50 values of >0.13 mg/l in fish, >0.1 mg/l in invertebrates and >0.12 mg/l in algae. It has reliable NOEC of ≥0.12 mg/l in algae and reliable long-term NOEC of ≥0.12 mg/l in Daphnia magna.
The available short- and long-term aquatic toxicity data indicate that there are no effects on aquatic organisms at the limit of solubility of the substance in water.
The substance hydrolyses slowly in water and is not readily biodegradable.
These data are consistent with the following classification under Regulation (EC) No 1272/2008 (as amended) (CLP):
Acute toxicity: Not classified.
Chronic toxicity: Not classified.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.
Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
