Registration Dossier

Ecotoxicological information

Ecotoxicological Summary

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Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.32 mg/L
Assessment factor:
1 000
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
3.2 mg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.032 mg/L
Assessment factor:
5 000
Extrapolation method:
assessment factor

STP

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

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
2 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Sediment (marine water)

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

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
0.22 mg/kg soil dw
Extrapolation method:
equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

The hazard assessment for the environment is based on the properties of the silanol hydrolysis product, 3-chloropropyl(methyl)silanediol, because the hydrolysis half-life of the registered substance is 1.3 hours at 20-25°C and pH 7. The substance will hydrolyse rapidly in contact with water and atmospheric moisture to form 3-chloropropyl(methyl)silanediol and methanol. REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT50 is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. REACH guidance, (ECHA 2017, R.7b) also suggests that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Therefore, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the silanol hydrolysis product, in accordance with REACH guidance. As described in the water solubility Section, condensation reactions of the silanediol are possible.

3-Chloropropyl(methyl)silanediol is highly water soluble (6.0E+04 mg/l (QSAR), limited by condensation reactions) and has low log Kow (0.8 at 20 °C) and low vapour pressure (0.018 Pa at 25°C).

In order to reduce 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 registered substance and the substance used as surrogate for read-across are part of a class of low functionality compounds acting via a non-polar narcosis mechanism of toxicity. The group of organosilicon substances in this group contain alkyl, aryl, alkoxy or hydroxy groups attached to the silicon (Si) atom when present in aqueous solution. Secondary features may be present in the alkyl chain (e.g. halogen, nitrile, unsaturated bonds) that do not affect the toxicity of the substances. The registered substance hydrolyses rapidly in water and therefore the selection of surrogate substance is based on log Kow of the resulting silanols and the chemical groups present in them. After hydrolysis has taken place the side chain of the registered and surrogate substances is a propyl chain with a methyl group at the end.

 

Additional information is given in a supporting report (PFA 2016y) attached in Section 13.

 

The analogue approach for fulfilling the data requirement by read-across is discussed in the RAAF report for ecotoxicity attached in Section 13 of IUCLID, according to the Read-across Assessment Framework (RAAF).

 

The registered substance (target substance), 3-chloropropyl(dimethoxy)methylsilane (CAS 18171-19-2), and the following substances used as surrogate for read-across (source substances), dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1) and 3-chloropropyl(diethoxy)methylsilane (CAS 13501-76-3), are part of a class of alkoxysilane and chlorosilane compounds which hydrolyse rapidly or moderately rapidly to produce the same silanol hydrolysis product and another non-Si hydrolysis product. 

 

In the context of the RAAF, the basis of the read-across hypothesis is “(Bio)transformation to common compound(s)”; Scenario 1 applies. The source substance hydrolyses to the same silicon containing hydrolysis product as the target substance, and the non-common hydrolysis products will not have an impact on the prediction of the ecotoxicological property.

 

This scenario covers the analogue approach for which the read-across hypothesis is based on (bio) transformation to common compound(s). For the REACH information requirement under consideration, the effects obtained in a study conducted with one source substance are used to predict the effects that would be observed in a study with the target substance if it were to be conducted. The same type of effect(s) or absence of effect is predicted. The predicted strength of the effects may be similar or based on a worst-case approach.

 

Table: Overview of physico-chemical and ecotoxicological properties of the registered substance and surrogate substances.

CAS Number

18171-19-2

7787-93-1

13501-76-3

Chemical Name

3-chloropropyl(dimethoxy)methylsilane

Dichloro(3-chloropropyl)methylsilane

3-chloropropyl(diethoxy)methylsilane

Si hydrolysis product

3-chloropropyl(methyl)silanediol

3-chloropropyl(methyl)silanediol

3-chloropropyl(methyl)silanediol

Molecular weight (parent)

182.72

g/mol

191.56

g/mol

210.78 g/mol

Molecular weight (hydrolysis product)

154.67 g/mol

154.67 g/mol

154.67 g/mol

log Kow (parent)

3.2

n/a

4.2

log Kow (silanol hydrolysis product)

0.8

0.8

0.8

Water sol (parent)

370 mg/l (QSAR)

n/a

36 mg/l

Water sol (silanol hydrolysis product)

60 000 mg/l (QSAR) (limited by condensation reactions above approximately 50 mg/l)

60 000 mg/l (QSAR) (limited by condensation reactions above approximately 50 mg/l)

60 000 mg/l (QSAR) (limited by condensation reactions above approximately 50 mg/l)

Vapour pressure (parent)

67.2 Pa at 20°C

83 Pa at 25°C (QSAR)

6.8 Pa at 25°C (QSAR)

Vapour pressure (hydrolysis product)

0.018 Pa at 25°C

0.018 Pa at 25°C

0.018 Pa at 25°C

Hydrolysis t1/2 at pH 7 and 20-25°C

1.3 hours

< 1 minute

9.5 hours

Hydrolysis t1/2 at pH 4 and 20-25°C

0.1 hour

< 1 minute

0.4 hour

Hydrolysis t1/2 at pH 9 and 20-25°C

0.03 hour

< 1 minute

0.2 hour

Short-term toxicity to fish (LC50)

n/a

 >107 mg/l

 574 mg/l

Short-term toxicity to aquatic invertebrates (EC50)

>100 mg/l

>100 mg/

295 mg/l

Algal inhibition (ErC50 and NOEC)

n/a

n/a

ErC50: 437 mg/l; NOEC: 57 mg/l

n/a = no data

 

Conclusion on classification

3-Chloropropyl(dimethoxy)methylsilane hydrolyses very rapidly and the silanol hydrolysis product is not readily biodegradable.

3-Chloropropyl(dimethoxy)methylsilane is not classified in the EU according to the Regulation (EC) No 1272/2008 because data for the substance and appropriate read-across data indicate that the silanol hydrolysis product is not toxic up to a concentration of 100 mg/l, i.e. lowest E(L)C50 is >100 mg/l. Additionally, the silanol hydrolysis product has log Kow <3.