Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.44 µg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.044 µg/L
Assessment factor:
100
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
100 mg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
3 mg/kg sediment dw
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
0.3 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:
PNEC soil
PNEC value:
0.164 mg/kg soil dw
Extrapolation method:
equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
insufficient hazard data available (further information necessary)

Additional information

Category read-across discussion

The registration substance has an average purity of >80% 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4), with <15% 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane Vi5-D5 (CAS 17704-22-2; Impurity 1) and <10% 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane Vi3-D3 (CAS 3901-77-7; Impurity 2) present as impurities. For each endpoint, the 3 components are considered separately.

2,4,6,8-Tetramethyl-2,4,6,8-tetravinyltetrasiloxane (Vi4-D4) hydrolyses slowly to form methylvinylsilanediol. The half-life value of 63 h at pH 7, 0.8 h at pH 9, and 1.1 h at pH 4 and 20 – 25°C is applicable to hydrolysis of the parent substance but complete reaction to methylvinylsilanediol will take longer. The water solubility of the substance is low (0.0073 – 0.0088 mg/l at 23°C), the measured vapour pressure is 93.5 Pa at 25°C, and the log Kow is high (6.5).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.

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 behaviour of 2,4,6,8-tetramethyl-2,4,6,8-tetravinyltetrasiloxane (Vi4-D4) in the environment is dominated by the high partition coefficient (log Kow6.5) and adsorption coefficient properties (log Koc4.1) of the substance.

In the following paragraphs the read-across approach for Vi4-D4 and its impurities are assessed taking into account structure and physico-chemical properties. Vi4-D4 and the substances used as surrogates are siloxanes. Substances in this group tend to have slow hydrolysis rates, low water solubility, high log Kow, high adsorption coefficients and a tendency for high persistence in the sediment compartment.

The physico-chemical and ecotoxicological properties and data of the registered and surrogate substances are summarised in the table below.

Aquatic toxicity: Read-across from octamethylcyclotetrasiloxane (D4) to Vi4-D4

Octamethylcyclotetrasiloxane (D4, CAS 556-67-2) is a cyclic siloxane made up of 4 Si with methyl groups, linked by oxygen atoms. Vi4-D4 is a cyclic siloxane made up of 4 Si with methyl and vinyl groups, linked by oxygen atoms. Vi4-D4 and D4 have slow hydrolysis rates (63 h at pH 7 and 20-25°C (predicted) and 69-144 h at pH 7 and 25°C, respectively) and similar physico-chemical properties: high molecular weight (MW 344.7 and 296.6 respectively), low water solubility (0.056 mg/l and 0.0073 – 0.0088 mg/l respectively) high log Kow(both 6.5) and high log Koc(both close to 4).The environmental behaviour and toxicity is driven by the water solubility, high log Kowand high log Koc,therefore read-across of aquatic and sediment toxicity data is considered to be appropriate.

The aquatic data indicates that D4 is toxic to aquatic organisms in the long-term in the range 4-7 µg/l. The lowest sediment toxicity study is withL. variegatuswhere a NOEC of 13 mg/kg dwt in natural sediment is reported.

Octamethylcyclotetrasiloxane is used to read-across to short-term toxicity to fish and long-term toxicity to fish and invertebrates endpoints. NOEC values of 0.0044, >= 0.0044 and 0.0079 mg/l, respectively, have been determined. D4 is also used to read-across to sediment toxicity endpoint.

Aquatic toxicity: Read-across from trimethoxyvinylsilane to Vi4-D4

To provide evidence that the vinyl side chain does not contribute significantly to the ecotoxicity of the registered substance, read-across from trimethoxyvinylsilane (CAS 2768-02-7) has been used. From the available dataset, the vinyl fragment of Vi4 -D4 is understood to not have any specific mode of action with respect to ecotoxicity; trimethoxyvinylsilane (CAS 2768-02-7) has L(E)C50values in the range 169-210 mg/l, which are consistent with non-polar narcosis as seen with other alkoxysilanes.

Trimethoxyvinylsilane is used to read-across to short-term toxicity to fish, invertebrates and algae endpoints. E(L)C50values of 191, 169 and 210 mg/l, respectively, have been determined.

Aquatic, sediment and terrestrial toxicity: Read-across from decamethylcyclopentasiloxane (D5) to Impurity 1, Vi5-D5

Decamethylcyclopentasiloxane (D5, CAS 541-02-6) is a cyclic siloxane made up of 5 Si with methyl groups, linked by oxygen atoms. Impurity 1, Vi5-D5 is a cyclic siloxane made up of 5 silicon atoms with methyl and vinyl groups, linked by oxygen atoms. Vi5-D5 and D5 have slow hydrolysis rates (1600 h at pH 7 and 20-25°C, predicted and 1590 h at pH 7 and 25°C respectively) and similar physico-chemical properties: high molecular weight (MW 431 and 370.8 respectively), low water solubility (9.1E-06 mg/l and 0.017 mg/l respectively) high log Kow(9.0 and 8.0 respectively) and high log Koc(6 and 5.2 respectively). D5 and Vi5-D5 are structural analogues with very similar properties. The environmental behaviour and toxicity is driven by the water solubility, high log Kowand high log Koc, therefore read-across of aquatic, sediment and terrestrial toxicity data is considered to be appropriate. The aquatic data indicates that D5 is not toxic to aquatic organisms in the long-term up to the limit of solubility. The lowest sediment toxicity study is withC. Ripariuswhere a NOEC of 70 mg/kg dwt in artificial sediment is reported. The lowest terrestrial toxicity study result is withF. candidawhere a NOEC of 377 mg/kg dry weight is reported.

Aquatic toxicity: Read-across from hexamethylcyclotrisiloxane (D3) to Impurity 2, Vi3-D3

Hexamethylcyclotrisiloxane (D3, CAS 541-05-9) is a cyclic siloxane made up of 3 Si with methyl groups, linked by oxygen atoms. Vi3-D3 is a cyclic siloxane made up of 3 silicon atoms with methyl and vinyl groups, linked by oxygen atoms. Vi3-D3 and D3 have rapid hydrolysis rates (0.6 h at pH 7 and 20-25°C, predicted and 23 minutes at pH 7 and 25°C, measured respectively) and similar physico-chemical properties: similar molecular weight (MW 259 and 223 respectively), low water solubility (0.13 mg/l and 2 mg/l respectively) and high log Kow(6.7 and 4.4 respectively). D3 and Vi3-D3 are structural analogues with very similar properties. The environmental behaviour and toxicity is driven by the water solubility and log Kow, therefore read-across of aquatic toxicity data is considered to be appropriate.

Consideration of low functionality side chains and reactive groups

Vinyl group: From the available dataset in the whole of the silanes and siloxanes database, vinyl fragments are understood to not have any specific mode of action with respect to ecotoxicity. For example, trimethoxyvinylsilane (CAS 2768-02-7) is an alkoxysilane with vinyl groups and a log Kow1.1. Short-term toxicity data for the substance report L(E)C50values in the range >89 - 191 mg/l (MoE Japan 2006, Hüls 1993 and Dow Corning 1979), which are consistent with non-polar narcosis as seen with other alkoxysilanes.

 


Table: Summary of physicochemical and ecotoxicological properties for the constituents of the registered substance and their surrogate substances.

CAS Number

2554-06-5

556-67-2

2768-02-7

17704-22-2

541-02-6

3901-77-7

541-05-9

Chemical Name

2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane

Octamethylcyclotetrasiloxane

trimethoxyvinylsilane

2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane (Impurity 1 (Vi5-D5))

Decamethylcyclopentasiloxane (D5)

2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane (Impurity 2 (Vi3-D3))

Hexamethylcyclotrisiloxane (D3)

Ultimate Si hydrolysis product

Methylvinylsilanediol

Dimethylsilanediol

vinylsilanetriol

Methylvinylsilanediol

Dimethylsilanediol

Methylvinylsilanediol

Dimethylsilanediol

Molecular weight (parent)

344.66

296.62

148.2

431

370.8

259

223

Molecular weight (hydrolysis product)

104.18

92.17

106.2

104.18

92.17

104.18

92.17

log Kow(parent)

6.47

6.49

1.1

9.0

8.0

6.7

4.4

Water sol (parent)

0.0073 – 0.0088 mg/l at 23°C

0.056 mg/l

l9400 mg/l

 

9.1E-06 mg/l

0.017 mg/l

0.13 mg/l

2 mg/l

Vapour pressure (parent)

93.5 Pa

132 Pa

1190 Pa

0.6 Pa

33 Pa

67 Pa

671 Pa

Hydrolysis t1/2at pH 7 and 25°C

approximately 63 hours

69-144 hours

0.2 h (at 20C)

1600 hours

1590 hours

0.6 hours

23 minutes

Hydrolysis t1/2at pH 4 and 25°C

1.1 hours

1.8 hours

0.04 h

3.3 hours (pH5)

9.3 hours

0.1 hours

2 minutes

Hydrolysis t1/2at pH 9 and 25°C

0.8 hours

0.7-0.8 hours

0.004 h

11 hours

24.8-31.6 hours

0.02 hours

0.4 minutes

Short-term toxicity to fish (LC50)

LL50>1000 mg/l loading rate (WAFs), equivalent to >7.3 mg/l*

10 µg/l

191 mg/l

n/a

>16 µg/l (>LOS)

n/a

>1.6 mg/l (>LOS)

Short-term toxicity to aquatic invertebrates (EC50)

EL50272 mg/l loading rate (WAFs) *

15 μg/l

169 mg/l

n/a

>2.9 µg/l (>LOS)

n/a

>1.6 mg/l (>LOS)

Algal inhibition (ErC50and NOEC)

EL50(70.5 h): >988 mg/l NOELR: ≥988 mg/l*

>22 µg/l

210 mg/l

n/a

96-h EC50 >12 µg/l and 96-h NOEC ≥12 µg/l. (>LOS)

n/a

>1.6 mg/l (>LOS)

Long-term toxicity to fish (NOEC)

≥0.0044 mg/l

≥4.4 μg/l

n/a

n/a

≥14 µg/l (>LOS)

n/a

n/a

Long-term toxicity to aquatic invertebrates (NOEC)

0.0079 mg/l

NOEC 7.9 µg/l

n/a

n/a

≥15 µg/l (>LOS)

n/a

n/a

Sediment toxicity (NOEC)

≥100 mg/kg dry weight, Hyalella azteca

13 mg/kg dry weight,Lumbriculus variegatus44 mg/kg dry weight,Chironomus riparius

n/a

n/a

Chironomus riparius

70 mg/kg dry weight,

n/a

n/a

Terrestrial toxicity (NOEC or EC50)

n/a

n/a

n/a

n/a

F. Candidia

377 mg/kg dry weight

n/a

n/a

 * The studies have been conducted at loading rates above the solubility limit of the substance. The studies indicate that the substance is not toxic at the limit of solubility.

Conclusion on classification

The data set at present has some uncertainty:

Reliable ecotoxicity conclusions are read across from a structural analogue of higher water solubility. These long-term no observed effect concentrations for aquatic organisms are very close to the limit of water solubility for the registration substance, and it is not possible to conclude with confidence whether the NOECs will be above or below the limit of solubility for the registration substance.

Further testing of long-term aquatic effects of the registration substance has been proposed to resolve this uncertainty.

Conclusions for classification and labelling for the environment for the registration substance will therefore be finalised in a future update, once the new long-term aquatic testing has been conducted.