Registration Dossier

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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Hazard for aquatic organisms


Hazard assessment conclusion:
no hazard identified

Marine water

Hazard assessment conclusion:
no hazard identified


Hazard assessment conclusion:
no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
8.9 mg/kg sediment dw
Assessment factor:
Extrapolation method:
assessment factor

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
0.89 mg/kg sediment dw
Assessment factor:
Extrapolation method:
assessment factor

Hazard for air


Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms


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:

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.


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



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)



Molecular weight (hydrolysis product)



log Kow (parent)



log Kow (silanol hydrolysis product)



Log Koc (parent)



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


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)



Long-term terrestrial toxicity (NOEC)



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.