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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

Sediment (marine water)

Hazard assessment conclusion:
no hazard identified

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:
no potential to cause toxic effects if accumulated (in higher organisms) via the food chain

Additional information

Category read-across discussion

The hydrolysis half-life of dodecamethylpentasiloxane (L5, CAS 141-63-9) is 30 days at pH 7 and 25⁰C. The water solubility of the substance is low (70 ng/l) and the log Kow is high (9.3-9.5). Due to the slow hydrolysis half-life, the chemical safety assessment is based on the parent substance.

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.


In order to reduce 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, dodecamethylpentasiloxane hydrolyses very slowly in water (half-life 728 hours at pH 7 and 25°C).

The registration substance (L5) and the substance 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 in the sediment compartment. For substances with a log Kow of 8 and above no long-term toxicity 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 2017) attached in Section 13 of the IUCLID dossier. This report also 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 read-across approach for dodecamethylpentasiloxane is assessed for the surrogate substance taking into account structure, hydrolysis rate and physico-chemical properties.

Read-across from L4 to L5: (Aquatic toxicity)

The registered substance, dodecamethylpentasiloxane (L5, CAS 141-63-9) and the surrogate substance decamethyltetrasiloxane (L4, CAS 141-62-8) are linear siloxanes with 5 and 4 silicon atoms respectively, with methyl branches and alternated by oxygen. L5 and L4 possess similar physico-chemical properties: high molecular weight (350 and 310 respectively), low water solubility (both insoluble, at 7.0E-05 mg/l and 6.7E-04 mg/l respectively), higher log Kow (9.3-9.5 and 8.2 respectively) and high log Koc (both 5.16). Both substances have negligible biodegradability and similar low hydrolysis rates. A comparison of the key physicochemical properties is presented in the table below.

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. Given the similar properties and structural similarities, it is considered valid to read-across data from decamethyltetrasiloxane (L4) to dodecamethylpentasiloxane (L5).

Toxicity to aquatic algae data and long-term toxicity to fish data have been read across from L4.

Table: Summary of aquatic ecotoxicological and physico-chemical properties for the registered substance, its hydrolysis products and the surrogate substances.

CAS Number



Chemical Name

Dodecamethylpentasiloxane (L5)

Decamethyltetrasiloxane (L4)

Si hydrolysis product

Dimethylsilanediol and trimethylsilanol

Note: the properties reported below in rows for ‘silanol hydrolysis product’ relate to dimethylsilanediol. For properties of trimethylsilanol, see next column)

Dimethylsilanediol and Trimethylsilanol

Note: the properties reported below in rows for ‘silanol hydrolysis product’ relate to trimethylsilanol. For properties of dimethylsilanediol, see previous column)

Molecular weight (parent)



Molecular weight (hydrolysis product)



log Kow(parent)



log Kow(silanol hydrolysis product)



Log Koc(parent)



Water sol (parent)

7.0E-05 mg/l

0.00674 mg/l

Water sol (silanol hydrolysis product))

1.0E+06 mg/l

995 mg/l

Vapour pressure (parent)

7.8 Pa

73 Pa

Vapour pressure (hydrolysis product)

7 Pa

1900 Pa

Hydrolysis t1/2 at pH 7 and 25°C

728 hours

728 hours

Short-term toxicity to fish (LC50)

>75 ng/l

6.3 μg/l

Short-term toxicity to aquatic invertebrates (EC50)



Algal inhibition (ErC50 and NOEC)


EC50: >2.2 μg/l; NOEC: ≥2.2 μg/l

Long-term toxicity to fish (NOEC)

≥39 ng/l

≥5.3 μg/l 

Long-term toxicity to aquatic invertebrates (NOEC)

≥47 ng/l

≥4.9 μg/l

Sediment toxicity (NOEC)

(normalised to 5% OC)

≥38 mg/kg dwt, Lumbriculus variegatus;

≥27 mg/kg dwt, Chironomus riparius;

≥59 mg/kg dwt, Hyalella azteca.

92 mg/kg dwt Hyalella azteca

≥ 34 mg/kg dwt Lumbriculus variegatus;

Short-term terrestrial toxicity (L(EC)50)



Long-term terrestrial toxicity (EC10)

EC10 >1000 mg/kg dw, Eisenia fetida (OECD 222);

EC10 >100 mg/kg dw, soil microorganisms (OECD 216)

EC10 >1000 mg/kg dw,Eisenia fetida (OECD 222);

EC10 >100 mg/kg dw, soil microorganisms (OECD 216)

Conclusion on classification

The substance has reliable short-term E(L)C50 values of >75 ng/l in fish and >2.2 μg/l in algae. It has a reliable NOEC value of ≥2.2 μg/l in algae and reliable long-term NOEC values of ≥47 ng/l in Daphnia and ≥7.9 μg/l in fish (algae, Daphnia and long-term fish data are read-across from an analogous substance).

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