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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

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:
no hazard identified

Sediment (marine water)

Hazard assessment conclusion:
no hazard identified

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

Additional information

The hydrolysis half-life of tetradecamethylhexasiloxane (L6, CAS 107-52-8, EC 203 -499 -5) is 6300 hours at pH 7 and 25 °C. The water solubility of the substance is low (0.0000023 mg/l) and the log Kow is high (>9.41 at 25 °C, read across from L5, CAS 141-63-9, EC 205-492-2). 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 registration substance.

READ-ACROSS JUSTIFICATION

In order to reduce testing read-across is proposed to fulfil up to REACH Annex VIII 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, tetradecamethylhexasiloxane hydrolyses very slowly in water (half-life 6300 hours at pH 7 and 25 °C).

Tetradecamethylhexasiloxane and the substances 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 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.

In the following paragraphs the read-across approach for tetradecamethylhexasiloxane is assessed for the surrogate substances taking into account structure, hydrolysis rate and physico-chemical properties.

Additional information is given in a supporting report (PFA, 2017at) attached in Section 13.

Read-across from L4 to L6:

The registered substance, tetradecamethylhexasiloxane (L6, CAS 107-52-8) and the surrogate substance decamethyltetrasiloxane (L4, CAS 141-62-8, EC 205-491-7) are linear siloxanes with 6 and 4 silicon atoms respectively, with methyl branches and alternated by oxygen. L6 and L4 possess similar physico-chemical properties: high molecular weight (459 g/mol and 310.69 g/mol respectively), low water solubility (both insoluble, at 2.3E-06 mg/l and 6.7E-03 mg/l respectively), high log Kow (>9.41 at 25°C (by read across from L5) and 8.21 at 25.1°C respectively) and high log Koc ( >6.0 and 5.16 respectively). Both substances have negligible biodegradability and similar slow hydrolysis rates at environmentally relevant temperature and pH.

No effects have been reported at the limit of solubility in short-term and long-term studies in fish, Daphnia and algae conducted with L4. Given the similar properties and structural similarities, it is considered valid to read-across data from decamethyltetrasiloxane (L4) to tetradecamethylhexasiloxane (L6).

 

Read-across from L5 to L6:

The registration substance, tetradecamethylhexasiloxane (L6, CAS 107-52-8) and the surrogate substance dodecamethylpentasiloxane (L5, CAS 141-63-9) are linear siloxanes with 6 and 5 silicon atoms respectively, with methyl branches and alternated by oxygen. L6 and L5 possess similar physico-chemical properties: high molecular weight (459 g/mol and 384.85 g/mol respectively), low water solubility (both insoluble, at 2.3E-06 mg/l and 7.0E-05 mg/l respectively), high log Kow (both >9.0 at 20°C; the log Kow of L5 is 9.41 at 25°C, (measured), and this result is read across to L6) and high log Koc ( >6.0 and 6.3 respectively). Both substances have negligible biodegradability and similar slow hydrolysis rates at environmentally relevant temperature and pH.

No effects have been reported at the limit of solubility in short-term and long-term studies in fish, Daphnia and algae conducted with L5. Given the similar properties and structural similarities, it is considered valid to read-across data from dodecamethylpentasiloxane (L5) to tetradecamethylhexasiloxane (L6).

 

Table 3 Summary of aquatic ecotoxicological and physico-chemical properties for the registered substance, its hydrolysis products and the surrogate substances.

CAS Number

107-52-8

141-63-9

141-62-8

Chemical Name

Tetradecamethylhexasiloxane (L6)

Dodecamethylpentasiloxane (L5)

Decamethyltetrasiloxane (L4)

Si hydrolysis product

Dimethylsilanediol (CAS 1066-42-8) and trimethylsilanol (CAS 1066-40-6)

Dimethylsilanediol (CAS 1066-42-8) and trimethylsilanol (CAS 1066-40-6)

Dimethylsilanediol (CAS 1066-42-8) and trimethylsilanol (CAS 1066-40-6)

Molecular weight (parent) g/mol

459

384.85

310.69

log Kow (parent)

>9.41 (read across from L5)

9.41

8.21

Log Koc (parent)

>6.0

6.3

5.16

Water sol (parent)

2.3E-06 at 20°C

7.0E-05 mg/l at 23°C

6.7E-03 mg/l at 23°C

Vapour pressure (parent)

 0.27 Pa at 20°C

7.8 Pa at 25°C (QSAR prediction)

73 Pa at 25°C

Hydrolysis t1/2 at pH 7

6300 hours at 20 -25°C, predicted

>728 hours at 25°C, read-across from L4

728 hours at 25°C, measured

Short-term toxicity to fish (LC50)

n/a

>75 ng/l

>6.3 μg/l

Short-term toxicity to aquatic invertebrates (EC50)

n/a

n/a

n/a

Algal inhibition (ErC50 and NOEC)

n/a

n/a

EC50: >2.2 μg/l; NOEC: ≥2.2 μg/l

Long-term toxicity to fish (NOEC)

n/a

≥39 ng/l (reported in a bioconcentration study)

≥7.9 μg/l 

Long-term toxicity to aquatic invertebrates (NOEC)

n/a

≥47 ng/l

≥4.9 μg/l

Sediment toxicity (NOEC) (normalised to 5% OC)

n/a

≥38 mg/kg dry weight,Lumbriculus variegatus;

≥27 mg/kg dry weight,Chironomus riparius;

≥52 mg/kg dry weight,Hyalella azteca.

≥92 mg/kg dwtHyalella azteca

≥ 34 mg/kg dwt Lumbriculus variegatus;

Short-term terrestrial toxicity (L(E)C50)

n/a

n/a

n/a

Long-term terrestrial toxicity (NOEC)

n/a

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 >0.000075 mg/l in fish and >0.0022 mg/l in algae based on read-across from structural analogues. It has a reliable NOEC of ≥0.0022 mg/l in algae and reliable long-term NOECs of ≥0.000047 mg/l in Daphnia and ≥0.0079 mg/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.