Registration Dossier
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EC number: 208-762-8 | CAS number: 540-97-6 D6
- 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:
- PNEC STP
- PNEC value:
- 1 mg/L
- Assessment factor:
- 100
- Extrapolation method:
- assessment factor
Sediment (freshwater)
- Hazard assessment conclusion:
- PNEC sediment (freshwater)
- PNEC value:
- 13 mg/kg sediment dw
- Assessment factor:
- 10
- Extrapolation method:
- assessment factor
Sediment (marine water)
- Hazard assessment conclusion:
- PNEC sediment (marine water)
- PNEC value:
- 1.3 mg/kg sediment dw
- Assessment factor:
- 500
- Extrapolation method:
- assessment factor
Hazard for air
Air
- Hazard assessment conclusion:
- no hazard identified
Hazard for terrestrial organisms
Soil
- Hazard assessment conclusion:
- PNEC soil
- PNEC value:
- 3.77 mg/kg soil dw
- Assessment factor:
- 100
- Extrapolation method:
- assessment factor
Hazard for predators
Secondary poisoning
- Hazard assessment conclusion:
- PNEC oral
- PNEC value:
- 66.7 mg/kg food
- Assessment factor:
- 300
Additional information
The hydrolysis half-life of dodecamethylcyclohexasiloxane (D6) is >1 year at pH 7 and 25˚C. The water solubility of the substance is low (ca. 5 µg/l) and the log Kowis high (8.87). It is therefore likely that, under the flow-through exposure conditions of the aquatic toxicity tests reported in the following sections, that the test organisms will have been predominately exposed to very low concentrations of the registered substance.
READ-ACROSS JUSTIFICATION
In order to reduce animal testing read-across is proposed to fulfil up to REACH Annex X requirements for the registered substance from substances that have similar structure and physicochemical properties. Ecotoxicological studies are conducted in aquatic medium or in moist environments; therefore the hydrolysis rate of the substance is particularly important since after hydrolysis occurs the resulting product has different physicochemical properties and structure.
In aqueous media, D6 hydrolyses very slowly in water (half-life >1 year at pH 7 and 25°C).
D6 and the substance used as surrogate for read-across are part of a class of compounds called siloxanes. Substances in this group tend to have low water solubility, high adsorption and partition coefficientsand slow degradation in the sediment compartment. For substances with a log Kowof 8 and above no long-term toxicity effects are seen with aquatic organisms due to the low water solubility limiting the effects seen. In the environment the substances will adsorb to particulate matter and will partition to soil and sediment compartments.
In the following paragraphs the read-across approach for D6 is assessed for the surrogate substance taking into account structure, hydrolysis rate and physico-chemical properties.
Additional information is given in a supporting report (PFA, 2015i) attached in Section 13 of the IUCLID 5 dossier.
Consideration of low functionality side chains and reactive groups
Vinyl group: From the available dataset in the whole of the silanes and siloxanes database, vinyl fragments are understood to not have any specific mode of action with respect to ecotoxicity. For example, trimethoxyvinylsilane (CAS 2768-02-7) is an alkoxysilane with vinyl groups and a log Kow1.1. Short-term toxicity data for the substance report L(E)C50values in the range 169-210 mg/l (Dow Corning 1979 and Hüls 1993), which are consistent with non-polar narcosis as seen with other alkoxysilanes.
Phenyl group: The toxicity of phenyls is also related to non-polar narcosis. The toxicity of substances with phenyl groups increases with increasing log Kow. For example, trichlorophenylsilane (CAS 98-13-5) has a very fast hydrolysis rate and the log Kowof the hydrolysis product is -0.2. Short-term toxicity data with trichlorophenylsilane determine no effects up to 100 mg/l (Springborn Smithers 2009a, b and c).
Si-H reaction: Some of the substances can undergo a Si-H reaction. For example, trimethoxysilane (CAS 2487-90-3) is a substance that undergoes strong Si-H bond reaction and with a log Kowvalue 0.2 for the parent and -2.9 for hydrolysis product. Short-term toxicity data with trimethoxysilane determine no effects up to 100 mg/l (Springborn Smithers 2004a, b and c). This indicates that the Si-H further reaction does not have any specific mode of action with respect to ecotoxicity. This conclusion is relevant for siloxanes as well as alkoxysilanes such as trimethoxysilane.
Read-across from decamethylcyclopentasiloxane (D5) to dodecamethylcyclohexasiloxane (D6):
The registered substance, dodecamethylcyclohexasiloxane (D6, CAS 540-97-6) and the surrogate substance decamethylcyclopentasiloxane (D5, CAS 541-02-6) are cyclic siloxanes. D6 is a cyclic siloxane with six dimethylated silicon atoms linked by six oxygen atoms. D5 is a directly analogous structure with five silicon and five oxygen atoms. The substances have similar physicochemical properties: high molecular weight (445 and 370 respectively), low water solubility (both insoluble, at 0.0051 and 0.017 mg/l respectively), high log Kow(8.87 and 8.02 respectively) and high log Koc(5.9 and 5.2 respectively). Both substances have negligible biodegradability and similar slow hydrolysis rates.
No effects at the limit of solubility have been reported in short-term and long-term studies in other trophic levels conducted with both substances. Environmental toxicity data for siloxanes are consistent with a non-polar narcosis mechanism (Redman 2012,Peter Fisk Associates 2013bc). Given the similar properties, structural similarities, and expected mode of action it is considered valid to read-across data from decamethylcyclopentasiloxane (D5) to dodecamethylcyclohexasiloxane (D6).
Table 1. Summary of ecotoxicological and physicochemical properties for the registered substance and the surrogate substance(aquatic and terrestrial toxicity)
CAS Number | 541-02-6 | 540-97-6 |
Chemical Name | Decamethylcyclopentasiloxane (D5) | Dodecamethylcyclohexasiloxane (D6) |
Si hydrolysis product | Dimethylsilanediol | Dimethylsilanediol |
Molecular weight (parent) | 370.78 | 444.93 |
Molecular weight (hydrolysis product) | 92.17 | 92.17 |
log Kow(parent) | 8.02 | 8.87 |
log Kow(silanol hydrolysis product) | -0.41 | -0.38 |
log Koc(parent) | 5.2 | 5.9 |
Water sol (parent) | 0.017 mg/l | 0.0051 mg/l |
Water sol (silanol hydrolysis product)) | 1.0E+06 mg/l | 1.0E+06 mg/l |
Vapour pressure (parent) | 33.2 Pa | 5 Pa |
Vapour pressure (hydrolysis product) | 7 Pa | 7 Pa |
Hydrolysis t1/2at pH 7 and 25°C | 1590 h | >1 year |
Short-term toxicity to fish (LC50) | >16 µg/l | n/a |
Short-term toxicity to aquatic invertebrates (EC50) | >2.9 µg/l | n/a |
Algal inhibition (ErC50and NOEC) | ErC50: >12 μg/l; NOEC: ≥12 μg/l | EC50: >2.0 μg/l; NOEC: ≥2.0 μg/ |
Long-term toxicity to fish (NOEC) | ≥14 μg/l | n/a |
Long-term toxicity to aquatic invertebrates (NOEC) | ≥15 µg/l | ≥4.6 µg/l |
Sediment toxicity (NOEC) | 70 mg/kg dwt,C. riparius | <22 mg/kg dwt,C. riparius ≥420 mg/kg dwt,L. variegatus; |
Short-term terrestrial toxicity (L(EC)50) | (IC50 ) 209 mg/kg dwt,H. vulgare; | n/a |
Long-term terrestrial toxicity (NOEC) | ≥4074 mg/kg dwt, | n/a |
Conclusion on classification
D6 is not classified in the EU for environmental hazards according to Regulation (EC) No 1272/2008, as amended. The substance was found to be non-toxic at its functional water solubility limit in long-term studies with fish (using a surrogate test substance),Daphniaand algae.
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.
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