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EC number: 241-881-3 | CAS number: 17955-88-3
- 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
Endpoint summary
Administrative data
Description of key information
Additional information
The low water solubility, high log Kow and high log Koc of 1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane (CAS 17955-88-3) indicate that it will adsorb to organic matter and partition to sludges in a waste water treatment plant. No terrestrial toxicity test data are available with the registered substance.
Screening Assessment:
The registration substance falls within soil hazard category 3 as defined in REACH R.7; high absorption (log Kow >5) but there is no indication that the substance is very toxic to aquatic organisms. Aquatic toxicity data show no effects at concentrations that are close to or above the limit of water solubility of the substance. As discussed in Section 7.1.2.1, a true PNECaquatic cannot be calculated from the test data because the LC50/EC50 and NOEC values that have been determined are limit values. However, in order to conduct the screening assessment for terrestrial testing, an indicative PNECaqua is derived solely for this purpose. A PNECaqua(freshwater) value of ≥0.0000047 mg/l can be used to calculate a PNECsoil(screening) using the equilibrium partitioning approach.
PNECsoil |
= |
Ksoil-water |
* PNECaquatic(freshwater) * 1000 |
|
|
RHOsoil |
|
For 1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane this is:
PNECsoil(screening) |
= |
3.03E+04 |
* ≥0.0000047 * 1000 |
|
|
1700 |
|
= ≥0.084 mg/kg wwt
This is equivalent to ≥0.095 mg/kg dwt.
Using this PNECsoil(screening), the PECsoil x 10 / PNECsoil ratio is <1 (calculated value 1.11E-03). It should also be noted, that the soil toxicity data available with decamethylcyclopentasiloxane (D5, CAS 541-02-6) indicate that there is a good correlation between measured data and equilibrium partitioning derived PNECs. Therefore, even though the log Kow of the substance is >5 there is no indication that an additional assessment factor of 10 is needed to take into account possible uptake via soil ingestion.
In order to complete the screening assessment, a confirmatory long-term soil toxicity test is required. Terrestrial toxicity studies with siloxanes are considered to be 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. This is based both on chemical properties, and challenges encountered in studies of fate and ecotoxicity conducted to date with substances within this Category. 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.
Although test substance losses are expected during terrestrial testing with the registration substance, it is considered that it is possible that measurable concentrations will remain in the soil at the end of the eight-week test period for an OECD TG 222 study. An OECD TG 222 study is therefore proposed with the registration substance 1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane (CAS 17955-88-3). The need for further terrestrial toxicity testing (OECD TG 208) will be reviewed once the results of the OECD TG 222 study with the registration substance are available.
Effects on soil microorganisms are not anticipated. In aquatic toxicity testing, activated sludge (sewage treatment plant micro-organisms) do not appear to be affected by siloxanes. However, a toxicity to soil microorganisms study is proposed for the registration substance.
Until these data become available, there are no unacceptable risks for the soil compartment if the operational conditions and risk management measures described in Section 9 are applied.
PNECsoil for the registration substance has been derived based on read across from D5, which has similar physicochemical properties; the risk characterisation ratio (RCR) based on PNECsoil is <1.
Justification for interim read-across is given in Section 6 of IUCLID and Section 7.0 of the CSR. The read-across data are considered reliable and suitable for deriving an interim PNECsoil for the registered substance. The testing with D5 has been carried out with species that are representative of three taxonomic groups; earthworms, springtails and plants.
· 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 the test substance 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 test substance 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 IC50 value 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 D5 terrestrial 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 respectively). However the studies are considered to be suitable to derive an interim hazard and risk assessment under REACH.
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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