Amino functional alkoxysilanes

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2009-09-03 to 2009-09-03

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
53 µl of the test substance, Milli-RO water, synthetic sewage feed (16 ml) and activated sludge (200 ml) were mixed and made up to 500 ml with Milli-RO water in a 1 litre bottle.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Preparation of inoculum for exposure: The sludge was coarsely sieved to remove large particles. The sludge was then washed by centrifuging at 1000 g for 10 minutes. The supernatant was decanted and replaced with ISO-medium. The washing step was performed three times. The pH was 7.7 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

- Initial biomass concentration: 3.8 g/L

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

Oxygen consumption was measured and recorded for approximately 10 minutes.

Test temperature:

19.9-20.3°C

pH:

8.2 to 8.3

Nominal and measured concentrations:

100 mg/l (loading rate). Performance of a limit concentration at 100 mg/l is acceptable, because 100 mg/l exceeds the expected concentration in a Sewage Treatment Plant.

Details on test conditions:

Test vessel:
- Material, size, headspace, fill volume: glass, 300ml oxygen bottles, 1L test bottles

- Aeration: continuous

- No. of vessels per concentration (replicates): two

- No. of vessels per control (replicates): two

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: tap water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q)


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
After the 3-hour contact time, a well mixed sample of the contents of the reaction mixture was poured into a 300 ml oxygen bottle, and the flask was sealed with an oxygen electrode connected to a recorder, forcing the air out of the vessel. WTW inolab Oxi 730 supplied with a WTW CellOx 325 oxygen electrode, electrolyte type ELY/G

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 100 mg/L only, tested in duplicate

- Justification for using less concentrations than requested by guideline: No significant inhibition of respiration rate of the sludge was recorded for the test substance at a loading rate of 100 mg/L in both replicates and therefore no further testing was required.

Reference substance (positive control):

yes

Remarks:

(3,5-Dichlorophenol)

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The two controls had a difference in respiration rate of 6%, which is less than the 15% limit required by the guideline for a valid study.

Results with reference substance (positive control):

A positive control test with 3, 5-dichlorophenol yielded an EC50 of 8.7 mg/L, which is within the accepted range of 5 to 30 mg/l required by the guideline for a valid study.

Table 1: Results of the activated sludge respiration inhibition test

Test sample	Loading rate (mg/l)	Oxygen conc. at start (mg O2/l)	Oxygen consumption (mg O2/l/h)	% Inhibition respiration rate	pH
Initial control	0	7.3	34	-	8.3
Final control	0	6.5	32	-	8.2
Trimethoxy(methyl)silane replicate (1)	100	7.1	33	0	8.3
Trimethoxy(methyl)silane replicate (2)	100	7.1	31	6	8.3
3,5-dichlorophenol	5	-	-	38	-
	12	-	-	59	-
	30	-	-	72	-

 

 

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiration inhibition 3hr EC10 value of >100 mg/l (loading rate) was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1994-04-19 to 1994-04-20

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remarks'

Remarks:

The test procedure was described in sufficient detail and was in accordance with generally accepted scientific standards, with acceptable restrictions. The restrictions were that a reference substance was not used to check the sensitivity of the microorganisms. The study was conducted in compliance with GLP.

Principles of method if other than guideline:

Method: Oxygen consumption test (Huls method)

GLP compliance:

yes

Vehicle:

no

Details on test solutions:

Test substance was dissolved in water to give a stock solution of 50 mg/ml. This was pipetted in graded concentrations directly in the test flasks.

Test organisms (species):

Pseudomonas putida

Details on inoculum:

The bacterial culture was originally from the Institute for Water, Soil, and Air Hygiene of the BGA (Berlin).

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

5.75 h

Test temperature:

24.5-26.1 °C

Nominal and measured concentrations:

12.5, 25, 37.5 and 50 mg/l

Details on test conditions:

TEST SYSTEM
- Test vessel: 100 ml BOD bottles

- Type (delete if not applicable): closed

- No. of vessels per concentration (replicates): 4 with test substance (2 sterilised with HgCl2).

- No. of vessels per control (replicates): 4 without test substance and sterilised with HgCl2. 5 flasks without test substance or HgCl2.

- Biomass loading rate: 10 E+05 bacteria count/ml

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Oxygen concentration measured at end of test.

TEST CONCENTRATIONS
- Range finding study was used to determine the concentrations used in the main study

Reference substance (positive control):

no

Key result

Duration:

5.75 h

Dose descriptor:

EC10

Effect conc.:

13 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

5.75 h

Dose descriptor:

EC50

Effect conc.:

43 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Results with reference substance (positive control):

A positive control was not included.

Reported statistics and error estimates:

Regression analysis performed on results

Table 1Effect of test substance on oxygen consumption

Conditions	Concentration of test substance (mg/ml)	0	12.5	25	37.5	50
Test substance with HgCl2	Initial value*	8.24	8.28	8.22	8.14	8.17
	Difference**		-0.04	0.02	0.11	0.08
Test substance without HgCl2	Final value*	4.25	4.60	5.52	6.01	6.30
Oxygen consumption after incubation		3.99	3.69	2.7	2.15	1.86
Absolute difference after incubation			0.30	1.29	1.84	2.31
% effect			7.6	32.3	46.1	53.5

* Average of 2 (or four for control) cultures

** Difference between control and test values

Linear regression after Probit transformation

Measure value mg/ml	% effect	log 10	Probit	Expected Probit
12.5	7.6	1.0969	3.6245	3.7
25	32.3	1.3979	4.5442	4.4
37.5	46.1	1.6740	4.9024	4.9
50	53.5	1.6990	5.0876	5.2

 

Regression analysis: Log Concentration = a; Probit = y; y=a+bx

a = 0.98

b= 2.47

n= 4

r =0.9898

Conclusions:

A pseudomonas putida respiration inhibition 5.75 hour EC50 of 43 mg/l and EC10 of 13 mg/l were determined in a reliable study described in sufficient detail and conducted in accordance with generally accepted scientific standards, with acceptable restrictions. The restrictions were that a reference substance was not used to check the sensitivity of the microorganisms. The study was conducted in compliance with GLP.

Reference 3

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

08 December 2011 - 22 December 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

The batch of Bis(trimethoxysilylpropyl)amine tested was a clear colourless liquid with a purity of 96.9%.

The test substance was pipetted below the surface of the Milli-RO-water and stirred briefly to mix (5 minutes). Subsequently, synthetic sewage feed and sludge were added and the test was initiated applying a 3 hour contact time. Preferably, the solution of the test substance in water should be pH neutral. As discussed with the sponsor the pH of a test substance solution test was not adjusted to pH 7.5 ± 0.5.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105°C to determine the amount of suspended solids (3.0 g/l of sludge, as used for the test). The pH was 7.7 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Post exposure observation period:

After the 3-hour contact time, the oxygen consumption was recorded for a period of approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer.
The pH and temperature were determined in the remaining part of the reaction mixture. This procedure was repeated for all test/reference substance concentrations/loading rates and controls.

Test temperature:

Final test: between 18.1 and 22.3°C

pH:

Final test
Controls, before addition of sludge: between the pH was between 7.4 and 7.6.
Controls, after the 3 hour exposure periode the pH was between 7.9 and 8.2.

Test concentrations, before addition of sludge: between the pH was between 7.7 and 9.1.
Test concentrations, after the 3 hour exposure periode the pH was between 7.9 and 8.4.

Discussion:
Bis(trimethoxysilylpropyl)amine has a slight increasing effect on pH (up to 9.1).
In general, lower (<5) and higher pH values (> approx. 8.5) might increase the toxic effect on micro-organisms. Thus the inhibition of the respiration rate may be caused by the intrinsic toxicity of Bis(trimethoxysilylpropyl)amine and/or the effect of the pH.
Thus, testing as is described in this report includes both effects and is thus a worse case situation.

Dissolved oxygen:

The oxygen concentration at the start of measurement was at least 8.2 mg O2/l.

Oxygen consumption=Respiration rate (mg O2/l h):
Controls: 50 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 10 mg/l: 54 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 22 mg/l: 52 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 46 mg/l: 56 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 100 mg/l: 54 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 220 mg/l: 45 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 460 mg/l: 36 mg O2/l h
Bis(trimethoxysilylpropyl)amine at 1000 mg/l: 27 mg O2/l h

Nominal and measured concentrations:

Nominal loading rates: 10, 22, 46, 100, 200, 460 and 1000 mg/l.

Details on test conditions:

TEST SYSTEM
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: All glass
- Aeration:During exposure with clean, oil-free air
- No. of vessels per concentration (replicates):5
- No. of vessels per control (replicates): 6
- Biomass loading rate 1.5 g/l suspended solids in final test mixture

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap-water purified by reverse osmosis (Milli-RO
EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : The respiration rate from each vessel, in mg O2/l/hr, was calculated from the linear part of the respiration curve, which was generally between 2 and 7 mg O2/l.

TEST CONCENTRATIONS
- Test concentrations: Seven loading rates: 10, 22, 46, 100, 200, 460 and 1000 mg/l.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

220 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

loading rate

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

270 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

loading rate

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

other: EC20

Effect conc.:

420 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

loading rate

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

ca. 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

loading rate

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: estimated value

Duration:

3 h

Dose descriptor:

other: EC80

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

loading rate

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

No statistically significant inhibition of the respiration rate of the sludge was recorded at or below a loading rate of 220 mg Bis(trimethoxysilylpropyl)amine / litre (Bonferroni t-Test: α=0.05 Toxstat). At higher loading rates the inhibitory effect of Bis(trimethoxysilylpropyl)amine on aerobic waste water (activated sludge) bacteria increased with increasing loading rate, ranging from 27% inhibition at a loading rate of 460 mg/l to 46% at a loading rate of 1000 mg/l.

Results with reference substance (positive control):

The EC50 of 3,5-dichlorophenol was in the accepted range of 2 to 25 mg/l for total respiration (8.2 in the combined limit-range-finding test and 8.1 mg/l in the final test).

Reported statistics and error estimates:

ECx
For Bis(trimethoxysilylpropyl)amine the percentage inhibition was plotted against the logarithm of the loading rates. The EC10 and EC20, for the test substance, were determined using linear regression analysis. If available, the 95% confidence limits of the EC values were given. The EC50 and EC80, were estimated.

For the reference substance the percentage inhibition was plotted against the logarithm of the concentrations and the EC50 was determined using linear regression analysis.

NOEC estimation
The NOEC was based on statistical analysis of the data. Data obtained for the test concentrations were compared with those obtained for the control using TOXSTAT Release 3.5, 1996, D.D. Gulley, A.M. Boelter, H.L. Bergman.

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this present test Bis(trimethoxysilylpropyl)amine was not toxic to waste water (activated sludge) bacteria at or below a loading rate of 220 mg/l (NOEC).

The EC10 was at a loading rate of 270 mg/l.
The EC20 was at a loading rate of 420 mg/l.
The EC50 was estimated at a loading rate of approximately 1000 mg/l.
The EC80 was above a loading rate of 1000 mg/l.

Reference 4

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reason / purpose for cross-reference:

read-across source

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: whole substance

Reference 5

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

09 February 2012 - 09 February 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

The batch of Amino Functional Alkoxysilanes (tested as received), a clear light yellow liquid, was a mixture including reactants and species consistent with the various reaction products obtained by combining aminopropyltriethoxysilane, glycidoxypropyl-trimethoxysilane and methyltrimethoxysilane (information obtained by the sponsor). Since Amino Functional Alkoxysilanes may have the potential to be volatile (information obtained by the sponsor), the test substance was pipetted below the surface of Milli-RO-water (200 ml, tap water purified by reverse osmosis) and stirred briefly to mix (5 minutes) in closed dark brown bottles. The initial loading rates were 2.5 times the final loading rate. Subsequently, 16 ml synthetic medium, 250 ml sludge and Milli-RO water up to 500 ml were added resulting in the required loading rates. Optimal contact between the test substance and test organisms was ensured applying continuous aeration and stirring.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105°C to determine the amount of suspended solids (3.0 g/l of sludge, as used for the test). The pH was 7.4 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic medium was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

After the 3-hour contact time, the oxygen consumption was recorded for a period of approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer. The pH and temperature were determined in the remaining part of the reaction mixture.

Test temperature:

Between 18.1 and 20.3°C

pH:

Before addition of sludge: 7.6 - 8.5.
After the 3 hour exposure period: 7.7 - 8.3.

Dissolved oxygen:

The oxygen concentration at the start of measurements was at least 7.5 mg O2/l

Oxygen consumption:
Controls: 48 mg O2/l h (mean value)
Amino Functional Alkoxysilanes 10 mg/l: 53 mg O2/l h
Amino Functional Alkoxysilanes 100 mg/l: 45 mg O2/l h
Amino Functional Alkoxysilanes 1000 mg/l: 51 mg O2/l h (mean value)

Nominal and measured concentrations:

Nominal loading rates: 10, 100 and 1000 mg/l

Details on test conditions:

TEST SYSTEM

- Type (delete if not applicable): open

- Material, size, headspace, fill volume: All glass

- Aeration:During exposure with clean, oil-free air

- No. of vessels per concentration (replicates): 1 for 10 and 100 mg/l and 3 for 1000 mg/l

- No. of vessels per control (replicates): 2

- Biomass loading rate:1.5 g/l suspended solids in final test mixture

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Tap-water purified by reverse osmosis (Milli-RO)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

The respiration rate from each vessel, in mg O2/l/hr, was calculated from the linear part of the respiration curve, which was generally between 2 and 7 mg O2/l.

TEST CONCENTRATIONS

- Test concentrations: limit study at 10, 100 and 1000 mg/l

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

(loading rate)

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

(loading rate)

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

In the combined limit/range-finding test no inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg Amino Functional Alkoxysilanes per litre.

There was no significant oxygen uptake from abiotic processes and the results at 1000 mg/l with a nitrification inhibitor showed no heterotrophic inhibition of the respiration rate.

Results with reference substance (positive control):

The EC50 of 3,5-dichlorophenol was in the accepted range of 2 to 25 mg/l for total respiration (4.0 mg/l).

Reported statistics and error estimates:

ECx
For the reference substance the percentage inhibition was plotted against the logarithm of the concentrations and the EC50 was determined using linear regression analysis.

For Amino Functional Alkoxysilanes no EC50 could be calculated because the test substance proved to be non-toxic (EC50 > a loading rate of 1000 mg/l).

NOEC estimation
No statistical analysis of the data was performed as no inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg Amino Functional Alkoxysilanes per litre.

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this present test Amino Functional Alkoxysilanes was not toxic to waste water (activated sludge) bacteria up to and including a loading rate of 1000 mg/l (NOEC).

The EC50 exceeded a loading rate of 1000 mg/l.

Description of key information

Toxicity to microorganisms (whole substance): 3-hour ASRI EC₅₀ >1000 mg/L, NOEC ≥1000 mg/L (OECD 209), read across from analogous substance trimethoxy(methyl)silane and its reaction products with 3-aminopropyltriethoxysilane and [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (EC 946-755-8) (Desmares-Koopmans, 2012).

Silanol HP-X (produced by parent constituents A, D, E, F and G): 3-hour ASRI EC₁₀ >100 mg/L (loading rate) (OECD 209), read across from trimethoxy(methyl)silane (CAS 1185-55-3).

 

Silanol HP-Z (produced by parent constituents B): 5.75-hour EC₁₀ 13 mg/L (respiration inhibition test), read across from 3-aminopropyl(triethoxy)silane (CAS 919-30-2).

 

Silanols HP-W and HP-Y (produced by parent constituents C, D, E, F): 3-hour NOEC 220 mg/L, EC₁₀ 270 mg/L (OECD 209), read across from 3-(trimethoxysilyl)-N-[3-(trimethoxysilyl)propyl]-1-propanamine (CAS 82985-35-1).

 

Additional information

The submission substance, trimethoxy(methyl)silane and its reaction products with [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and 3-(trimethoxysilyl)propylamine (EC No. 945-567-3), is a UVCB substance. No toxicity to sewage treatment plant microorganisms data are available with the registered substance.

Reliable toxicity to sewage treatment plant microorganisms data are read-across to the registered substance as a whole, from trimethoxy(methyl)silane and its reaction products with 3-aminopropyltriethoxysilane and [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (EC 946-755-8). Under the conditions of the test, trimethoxy(methyl)silane and its reaction products with 3-aminopropyltriethoxysilane and [3-(2,3-epoxypropoxy)propyl]trimethoxysilane was not toxic to wastewater (activated sludge) bacteria up to and including a loading rate of 1000 mg/L (NOEC). 

The EC₅₀ exceeded a loading rate of 1000 mg/L. 

These read-across data are used in environmental risk assessment for registered the substance as a whole.

The registered substance, trimethoxy(methyl)silane and its reaction products with [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and 3-(trimethoxysilyl)propylamine (EC No. 945-567-3), and the read-across substance, trimethoxy(methyl)silane and its reaction products with 3-aminopropyltriethoxysilane and [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (EC 946-755-8), are both UVCB substances and are part of an analogue group of alkoxysilanes, the toxicity of which is related to log K_ow. Substances with alkyl and amino-alkyl side-chains are part of this group.

Both substances are complex reaction mixes. The read-across substance is comprised of methoxy-, ethoxy- or mixed methoxy/ethoxy silanes. The registered substance is comprised of methoxy silanes. All of the constituents that make up the registered substance are present in the read-across substance.

 

Read-across from trimethoxy(methyl)silane and its reaction products with 3-aminopropyltriethoxysilane and [3-(2,3-epoxypropoxy)propyl]trimethoxysilane (EC 946-755-8) to trimethoxy(methyl)silane and its reaction products with [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and 3-(trimethoxysilyl)propylamine (EC No. 945-567-3) is therefore directly relevant.

 

The constituents of the substance are expected to hydrolyse to some extent within the sewage treatment plant, as well as during the toxicity to aquatic microorganisms test, to silanol hydrolysis products and methanol. Available data on the constituents and/or analogue substance(s) are reported.

The substance has been divided into separate parent Blocks (A-G) depending on structure and properties.

All of the constituents share four final silanol hydrolysis products, plus methanol, after the hydrolysis of the parent constituents. Please see the attached document in IUCLID Section 13, which gives further details on structure and properties of the parent substance and its hydrolysis products.

For the purposes of risk characterisation it is therefore possible to group all of the constituents into four silanol Assessment Entities: methylsilanetriol (CAS 2445-53-6, EC No. 219-489-9), 3-aminopropylsilanetriol (CAS 58160-99-9, EC 261-145-5), disilyl(alkylamine)-heptol and trisilyl(alkylamine)-undecol. Data for each of the four silanol assessment entities are sourced from:

 

Methylsilanetriol (CAS 2445-53-6, EC 219-489-9): Silanol HP-X

An activated sludge respiration inhibition 3-hour EC₁₀ value of >100 mg/l (loading rate) was determined for trimethoxy(methyl)silane (CAS 1185-55-3), which is the same substance as Block A, in a reliable study conducted according to an appropriate test protocol (OECD 209), and in compliance with GLP (Desmares-Koopmans, 2009). In a secondary source to which reliability could not be assigned, an IC₅₀ value of >10000 mg/l was reported for trimethoxy(methyl)silane (Chandra, 1997).

Trimethoxy(methyl)silane is the single constituent of Block A, which rapidly hydrolyses to methylsilanetriol, which is Silanol HP-X.

 

3-Aminopropylsilanetriol (CAS 58160-99-9, EC 261-145-5): Silanol HP-Z

A respiration inhibition test in a single bacterial strain is available for 3-aminopropyl(triethoxy)silane (CAS 919-30-2). In this study, a Pseudomonas putida respiration inhibition 5.75-hour EC₅₀ of 43 mg/l and EC₁₀ of 13 mg/l were determined (Schoberl, 1994). The study was reliable and conducted in accordance with generally accepted scientific standards and described in sufficient detail and in compliance with GLP with acceptable restrictions. The restrictions were that a reference substance was not used to check the sensitivity of the microorganisms.

3-Aminopropyl(triethoxy)silane hydrolyses to 3-aminopropylsilanetriol, which is Silanol HP-Z, and ethanol.

 

To support this result for CAS 919-30-2, a second study with an analogous substance, triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5), is read across. Both substances hydrolyse rapidly and share the same silanol hydrolysis product, 3-aminopropylsilanetriol. The isocyanate in the read-across substance, triethoxy(3-isocyanatatopropyl)silane, undergoes very rapid hydrolysis (half-life of about 5 minutes) to form 3-aminopropyl(triethoxy)silane, CAS 919-30-2, and carbon dioxide. 3-Aminopropyl(triethoxy)silane then undergoes rapid hydrolysis to form 3-aminopropylsilanetriol and ethanol. This study reports an activated sludge respiration inhibition 3-hour NOEC value of 10 mg/l and EC₁₀ of 17 mg/l (Desmares-Koopmans, 2013). In addition, an IC₅₀ >5000 mg/l was reported in secondary literature (handbook) (Chandra, 1997). The original reference was not available for review and no further information is available. The reliability of this result is not assignable.

 

Trisilyl(alkylamine)-undecol: Silanol HP-W, and disilyl(alkylamine)-heptol: Silanol HP-Y

There are no reliable respiration inhibition of activated sludge studies for Silanols HP-W and HP-Y. Therefore, good quality data from 3-(trimethoxysilyl)-N-[3-(trimethoxysilyl)propyl]-1-propanamine (CAS 82985-35-1) have been read-across.

The influence of 3-(trimethoxysilyl)-N-[3-(trimethoxysilyl)propyl]-1-propanamine (CAS 82985-35-1) on the respiration rate of activated sludge was investigated according to OECD 209 and GLP (NOTOX B.V., 2012). The nominal test concentrations were 10, 22, 46, 100, 200, 460 and 1000 mg/l. No inhibition in respiration rate of the sludge was recorded up to 220 mg/l. Hence, the NOEC for 3-(trimethoxysilyl)-N-[3-(trimethoxysilyl)propyl]-1-propanamine is 220 mg/l. The EC₁₀ is 270 mg/l and the EC₅₀ is 1000 mg/l. These results are read-across to Silanols HP-W and HP-Y of the submission substance.

 

Ethanol and methanol do not have adverse effects on microorganisms (OECD 2004a and OECD 2004b).

 

Carbon dioxide, which is the by-product of the isocyanate read-across substance hydrolysis, is exempt from registration under REACH Article 2(7) (a) because it is a substance with sufficiently known information and it is considered to cause minimum risk due to its intrinsic properties. Carbon dioxide is therefore not assessed further.

 

Consideration of Parent Substance Constituents

The registered parent substance has been divided into separate parent Blocks depending on structure and properties: Block A, B, C, D, E, F and G. The constituents of the substance are expected to hydrolyse rapidly. There are reliable hydrolysis data for the constituents of Blocks A and B, indicating rapid hydrolysis. Chemical safety assessment for Blocks A and B is therefore based on the silanol hydrolysis products methylsilanetriol and 3-aminopropylsilanetriol, respectively. Additionally, the substance used to provide toxicity data for Silanol HP-X is trimethoxy(methyl)silane (CAS 1185-55-3), which is actually the same substance as Block A.

However, there is uncertainty around the hydrolysis rates for constituents C-G, therefore risk assessment has been performed on the parent constituents, in addition to the silanol hydrolysis products. This is discussed further in the ecotoxicological general discussion.

The approach for assessing the toxicity of parent Blocks C-G, and to carry out risk assessment, is therefore as follows:

- Use the existing set of data that is used for the hydrolysis products of the constituents of each Block and base the PNEC for the parent Block on this data, without molecular weight correction.

- Where the constituents of the Block produce more than one silanol hydrolysis product, PNECs are calculated from the data for each hydrolysis product and the most conservative PNEC is assessed.

- A separate exposure assessment and risk characterisation is carried out using the properties of the parent.

Data for assessment of the parent Block are as follows:

Constituents A, C, D, E, F and G: Data for methylsilanetriol (CAS 2445-53-6, EC 219-489-9) (Silanol HP-X) are used.

Constituents B and G2: Data for 3-aminopropylsilanetriol (CAS 58160-99-9, EC 261-145-5) (Silanol HP-Z) are used.

Constituents C, D, E and F: Data for trisilyl(alkylamine)-undecol (Silanol HP-W) and disilyl(alkylamine)-heptol (Silanol HP-Y) are used. 

 

The constituents and analogous read-across substances are within an analogue group of substances within which in general, there is some evidence of toxicity to microorganisms i.e. an effect concentration (EC) could be derived and was <1000 mg/l.

 

The table below presents microorganism toxicity data available for substances within this group.

 

Blocks B to G and the analogous read-across substances are members of these analogue groups.

 

It is therefore considered valid to read-across the results for 3-aminopropyltriethoxysilane (CAS 919-30-2) and bis(trimethoxysilylpropyl)amine (CAS 82985-35-1) to fill the data gap for Blocks B to G of the registration substance. Additional information is given in supporting report (PFA 2013l) attached in Section 13.

Table: Microorganism toxicity data for other relevant substances

CAS	Chemical Name (CAS Name)	Guideline Number	Test method	Species	Duration (hour)	Result: E(I)C50 (mg/l)	Result: NOEC (Or EC10/EC20) (mg/l)	PFA Klimisch code
27445-54-1	Cyclohexanamine,N-[(diethoxymethylsilyl)methyl]-	OECD 209	ASRI		3-hour - but stirred 24 hours	624.2 mg/l     (EC20 240.2 mg/l)		1
3068-78-8	N-[3-(Trimethoxysilyl)propylcyclohexylamine]	OECD 209	ASRI		3	>1000	EC20 = 203	1
157923-74-5	2,2-Dimethyl-4-(trimethoxysilyl)butylamine	OECD 209	ASRI		3	>1000	EC15 869. 17.5% inhibition at 1000.	1
227085-51-0	N-Ethyl-3-trimethoxysilyl-2-methylpropanamine	OECD 209	ASRI		3	>1000		1
919-30-2	3-Aminopropyltriethoxysilane	Huls AG method	oxygen consumption	P. putida	5.75	43	EC10 13	2
82985-35-1	Bis(trimethoxysilylpropyl)amine	OECD 209	ASRI		3	estimated value, approximately 1000	EC10 270 Nitrification control indicated that heterotrophic inhibition of respiration rate was lower than the total inhibition.	1
1760-24-3	N-(3-(Trimethoxysilyl)propyl)ethylenediamine	DIN 38 412, Part 8 (Pseudomonas cell multiplication inhibition test)	growth inhibition test	P. putida	16	67	EC10 25	1
	[N,N-Bis(trimethylsilyl)aminopropyl]methyldiethoxysilane	OECD 209	ASRI		3	>100		1
None19	Reaction mix (reaction mass of 6 benzylated amine silanes)	OECD 209; EC C.11	ASRI		3	569	130; EC20 172	1

References:

OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.

OECD (2004b): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

PFA (2013l). Peter Fisk Associates, STP Microorganism toxicity III-8 Analogue Group report, PFA.300.003.008