3-(diethoxymethylsilyl)propylamine

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.33 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

3.3 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.033 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

86.9 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1.3 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.13 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.07 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The hydrolysis half-life of 3-(diethoxmethylsilyl)propylamine is6 h at pH 7, 20-25⁰C. The registered substance will hydrolyse in contact with water and atmospheric moisture to3-(dihydroxymethylsilyl)propylamineand ethanol. REACH guidance (ECHA 2010A, 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”. TGD and ECHA guidance, (EC 2003, ECHA 2010A) also suggest 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 Section 1.3, the silanol hydrolysis products may be susceptible to condensation reactions.

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.

In moist medium, 3-(diethoxymethylsilyl)propylamine hydrolyses very rapidly (half-life 6 h at 20-25°C and pH 7) to 3-(dihydroxymethylsilyl)propylamine. 3-(Dihydroxymethylsilyl)propylamine is a silanediol with an amine side chain and a log K_ow of -0.9. The non-silanol hydrolysis product ethanol, is not expected to contribute to any adverse effects at the relevant dose levels. This is discussed further below.

In the following paragraphs the read-across approach for 3-(diethoxymethylsilyl)propylamine is assessed for the surrogate substance taking into account structure, hydrolysis rate and physico-chemical properties.

 

·        Read-across from 3-aminopropyltriethoxysilane to 3-(diethoxymethylsilyl)propylamine

3-(Diethoxymethylsilyl)propylamine (CAS 3179-76-8) and 3-aminopropyltriethoxysilane (CAS 919-30-2) both hydrolyse rapidly in contact with water (6 h at pH 7, 20-25⁰C, and 8.5 h at pH 7, 25⁰C respectively). The organosilicon hydrolysis products are 3-(dihydroxymethylsilyl)propylamine and 3-aminopropylsilanetriol respectively. 3-(dihydroxymethylsilyl)propylamine and 3-aminopropylsilanetriol are structural analogues, both containing a propylamine group. The additional methyl group in 3-(dihydroxymethylsilyl)propylamine means only that it has a slightly higher log K_ow than the analogous silanetriol but both values are still very low (see below).

The organosilicon hydrolysis products also share similar physicochemical properties: high water solubility, low log K_ow (-0.9 and -2.9 respectively) and low MW (135.2 and 137.2 respectively).

                                                        

·        considerations of the non-silanol hydrolysis products.

The other hydrolysis by-product is ethanol for both substances. Ethanol has been studied extensively in the public literature and it is not expected to be hazardous at the concentrations produced during standard environmental studies. The short-term EC₅₀and LC₅₀values for ethanol are in excess of 1000 mg/l (OECD 2004b - SIDS for ethanol, CAS 64-17-5).

Table 7.1 Summary of physico-chemical and ecotoxicological properties for registered and surrogate substances.

CAS Number	3179-76-8	919-30-2
Chemical Name	3-(diethoxymethylsilyl)propylamine	3-aminopropyltriethoxysilane
Si hydrolysis product	3-(dihydroxymethylsilyl)propylamine	3-aminopropylsilanetriol
Molecular weight (parent)	191.35	221.37
Molecular weight (hydrolysis product)	135.24	137.21
log Kow(parent)	2.5	1.7
log Kow(silanol hydrolysis product)	-0.9	-2.89
Water sol (parent)	5900 mg/l	5400 mg/l
Water sol (silanol hydrolysis product))	1E+06 mg/l	1E+06 mg/l
Vapour pressure (parent)	6.9 Pa	2 Pa
Vapour pressure (hydrolysis product)	2.2E-02 Pa	2.4E-04 Pa
Hydrolysis t1/2at pH 7 and 25°C	357 min	8.5 hours
Hydrolysis t1/2at pH 4 and 25°C	<3 min	0.8 hours (pH5)
Hydrolysis t1/2at pH 9 and 25°C	17 min	0.15 hours
Short-term toxicity to fish (LC50)	n/a	>934 mg/l
Short-term toxicity to aquatic invertebrates (EC50)	n/a	331 mg/l
Algal inhibition (ErC50and NOEC)	n/a	>1000 and 863 mg/l
Long-term toxicity to fish (NOEC)	n/a	n/a
Long-term toxicity to aquatic invertebrates (NOEC)	n/a	n/a
Long-term sediment toxicity (NOEC)	n/a	n/a
Short-term terrestrial toxicity (L(E)C50)	n/a	n/a
Long-term terrestrial toxicity (NOEC)	n/a	n/a

Conclusion on classification

The registered substance hydrolyses very rapidly in contact with moisture. The silanol hydrolysis product is not readily biodegradable and has a log K_ow<<3.

The registered substanceis notclassifiedfor the environment in the EU according to Regulation (EC) No. 1272/2008 because short-term data available for an appropriate surrogate substance indicates the EC₅₀ and LC₅₀ to be >100 mg/l.