Registration Dossier
Registration Dossier
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EC number: 203-497-4 | CAS number: 107-51-7
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:
- 1.7 mg/kg food
- Assessment factor:
- 300
Additional information
The hydrolysis half-life of octamethyltrisiloxane (L3, CAS 107-51-7) is 329 h (13.7 d) at pH 7, 9.76 h at pH 9, 5.09 h at pH 5 and 25°C. The water solubility of the substance is low (34 μg/l) and the log Kow is high (6.6). It is therefore likely that, under the flow-through exposure conditions of the fish and invertebrate tests that the test organisms will have predominantly exposed to the registered substance. In the static algal test, it is likely that exposure will have been predominantly to the registered substance and a small proportion of its hydrolysis products.
L3 is volatile with high Henry's Law Constant (1.62E+06 Pa m3mol-1 at 12°C) meaning significant losses from test systems are possible. Measures were taken to maintain exposure concentrations by conducting the key fish and invertebrate tests under flow-through conditions and the algal test under sealed conditions. The terrestrial tests carried out (soil micro-organisms and a stability test under OECD 222 conditions) show that the test item was not maintained in the test systems.
READ-ACROSS JUSTIFICATION
In order to reduce animal 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. 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.
The registration substance, and the substances used as surrogate for read-across, are members of the Reconsile Siloxanes Category. Substances in this category tend to have low water solubility, high adsorption and partition coefficients and slow degradation rates in the sediment compartment. For substances with a log Kow of 6 and above no effects are seen with aquatic organisms due to the substance 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.
Additional information is given in a supporting report (PFA 2017at) attached in Section 13 of the IUCLID 6 dossier.
Read-across from L4 to L3
The registered substance, L3 and the surrogate substance decamethyltetrasiloxane (L4, CAS 141-62-8) are linear siloxanes with 3 and 4 silicon atoms respectively, with methyl branches and alternated by oxygen. L3 and L4 possess similar physicochemical properties: high molecular weight (236 and 310 respectively), low water solubility (both insoluble, at 3.4E-02 mg/l and 6.7E-04 mg/l respectively), high log Kow (6.60 and 8.21 respectively) and high log Koc (4.34 and 5.16 respectively). Both substances have negligible biodegradability and similar slow hydrolysis rates. A comparison of the key physicochemical properties is presented in table 7.0.1 below. Given the similar properties and structural similarities, it is considered valid to read across data from L4 to L3.
Table7.0.1.Summary of ecotoxicological and physicochemical properties for the registered substance and the surrogate substance.
CAS Number |
107-51-7 |
141-62-8 |
Chemical Name |
Octamethyltrisiloxane (L3) |
Decamethyltetrasiloxane (L4) |
Si hydrolysis product |
Trimethylsilanol; dimethylsilanediol
Note: the properties reported below in rows for ‘silanol hydrolysis product’ relate to trimethylsilanol. For properties of dimethylsilanediol, see data reported for L4 hydrolysis product in next column |
Trimethylsilanol; dimethylsilanediol Note: the properties reported below in rows for ‘silanol hydrolysis product’ relate to dimethylsilanediol. For properties of trimethylsilanol, see data reported for L3 hydrolysis product in previous column |
Molecular weight (parent) |
236.54 |
310.69 |
Molecular weight (hydrolysis product) |
90.2 |
92.17 |
log Kow (parent) |
6.6 |
8.2 |
log Kow (silanol hydrolysis product) |
1.2 |
-0.41 |
Log Koc (parent) |
4.34 |
5.16 |
Water sol (parent) |
3.4E-02 mg/l |
0.00674 mg/l |
Water sol (silanol hydrolysis product)) |
9.9E+02 mg/l |
1.0E+06 mg/l |
Vapour pressure (parent) |
530 Pa |
73 Pa |
Vapour pressure (hydrolysis product) |
1.9 hPa |
7 Pa |
Hydrolysis t1/2 at pH 7 and 25°C |
329 h |
728 h |
Short-term toxicity to fish (LC50) |
>19.4 μg/l |
>6.3 μg/l |
Short-term toxicity to aquatic invertebrates (EC50) |
>20 μg/l |
n/a |
Algal inhibition (ErC50 and NOEC) |
EC50: >9.4 μg/l; NOEC: ≥9.4 μg/l |
ErC50: >2.2 μg/l; NOEC: ≥2.2 μg/l |
Long-term toxicity to fish (NOEC) |
≥27 μg/l |
≥7.9 μg/l |
Long-term toxicity to aquatic invertebrates (NOEC) |
≥15 μg/l |
≥4.9 μg/l |
Sediment toxicity (NOEC) (normalised to 5% OC) |
89 mg/kg dwt, C. riparius 61 mg/kg dwt, L. variegatus 95 mg/kg dwt, H. azteca |
92 mg/kg dwt, H. azteca |
Short-term terrestrial toxicity (L(EC)50) |
n/a |
n/a |
Long-term terrestrial toxicity (NOEC) |
n/a |
n/a |
Conclusion on classification
The substance has reliable short-term E(L)C50 values of >19 μg/l in fish, >20 μg/l in invertebrates and >9.4 μg/l in algae. It has reliable NOEC of ≥9.4 μg/l in algae and reliable long-term NOEC of ≥15 μg/l in Daphnia and ≥27 μg/l in fish. 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.
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