3-(trimethoxysilyl)propyl isocyanate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 September 2012 - 01 November 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 3-Isocyanatopropyltriethoxysilane tested was a clear, colourless liquid with a purity of 96.5%. No correction was made for the purity/composition of the test substance. The test substance was pipetted below the surface of the Milli-RO-water and stirred briefly to mix (5 minutes). 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 by applying continuous aeration and stirring.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Source:Municipal sewage treatment plant: 'Waterschap Aa en Maas', Heeswijk-Dinther, The Netherlands, receiving predominantly domestic sewage.
Preparation of the sludge: The sludge was coarsely sieved (1 mm), 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 (2.9 g/l of sludge, as used for the test). The pH was 7.3 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:

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 10-11 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 19 and 22°C

pH:

The pH in all test series, before addition of sludge was between 7.2 and 7.5. After the 3 hour exposure period the pH was between 7.7 and 8.2.

Dissolved oxygen:

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

Mean respiration rates:
Control: 28 mg O2/l/h
T 1: loading rate of 10 mg/l: 26 mg O2/l/h
T2: loading rate of 32 mg/l: 22 mg O2/l/h
T3 loading rate of 100 mg/l: 22 mg O2/l/h
T4: loading rate of 320 mg/l: 11 mg O2/l/h
T5: loading rate of 1000 mg/l: 3 mg O2/l/h

Nominal and measured concentrations:

Nominal concentrations at a loading rate of 10, 32, 100, 320 and 1000 mg/l and a control

Details on test conditions:

Vessels: All glass open bottles/vessels
Air supply: Clean, oil-free air.
Aeration: The aeration was adjusted in such a way that the dissolved oxygen concentration at the start was above 60-70% saturation (60% of air saturation is > 5 mg/l at 20°C) and to maintain the sludge flocs in suspension.
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).
The amount of suspended solids in the final test mixture was 1.45 g/l.
The final test was a standard test that did not include a nitrification inhibitor or abiotic conditions.
nr replicates loading rates for the control in the final test: 6
nr replicates for the test substance loading rates in the final test: 5

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

10 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.:

17 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: (3.5 - 84 mg/l)

Key result

Duration:

3 h

Dose descriptor:

other: EC20

Effect conc.:

31 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: (6.6 - 140 mg/l)

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

180 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: (41 - 760 mg/l)

Details on results:

No statistically significant inhibition of the respiration rate of the sludge was recorded at loading rate of 10 mg 3-Isocyanatopropyltriethoxysilane / litre (Bonferroni t-Test: a=0.05 Toxstat). At higher loading rates the inhibitory effect of 3-Isocyanatopropyltriethoxysilane on aerobic waste water (activated sludge) bacteria increased with increasing loading rates, ranging from 21% inhibition at a loading rate of 32 mg/l to 89% 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 (11 and 8.9 mg/l in the combined limit/range-finding and final test, respectively.

Reported statistics and error estimates:

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

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 3-Isocyanatopropyltriethoxysilane was not toxic to waste water (activated sludge) bacteria at or below a loading rate of 10 mg/l (NOEC). This was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

The EC10 was at a loading rate of 17 mg/l (95% confidence interval: 3.5 – 84 mg/l).
The EC20 was at a loading rate of 31 mg/l (95% confidence interval: 6.6 – 140 mg/l).
The EC50 was at a loading rate of 180 mg/l (95% confidence interval: 41 – 760 mg/l).

Description of key information

Toxicity to microorganisms: 3 hour NOEC 10 mg/L, EC10 17 mg/L (OECD 209; ASRI), read-across from an analogous substance

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

17 mg/L

Additional information

There are no reliable microorganism toxicity data available for 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6), therefore good quality data for the analogous substance, triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5), have been read across. Both substances hydrolyse very rapidly and share the same silanol hydrolysis product, 3-aminopropylsilanetriol. In view of the rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

The other hydrolysis products are methanol (CAS 67-56-1) and ethanol (CAS 64-17-5) respectively.

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

3-(Trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) and triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5) are within an analogue group of substances within which there is some evidence of toxicity to microorganisms, i.e. an effect concentration (EC) could be derived and was <1000 mg/L. Data are available for two substances, one of these substances indicates toxicity, the other substance does not. As a worst case, data will be read across from the substance that indicates toxicity.

The table below presents microorganism toxicity data for substances within the analogue group III-18 (code used to represent the different sub-classes of substances, based on structure/functionality) of chlorosilanes, siloxanes, silanes and alkoxysilanes etcetera with isocyanate functionality in the side chain after any very rapid hydrolysis has been accounted for.

3-(Trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) and triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5) are members of this analogue group.

It is therefore considered valid to read-across the results for triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013ah) attached in Section 13.

Table Microorganism toxicity data for substances within the relevant analogue group III-18 of chemical:

CAS	Chemical Name (CAS Name)	Guideline Number	Test method	Klimisch code	Year	Duration	Result: E(I)C50 (mg/L)	Result: NOEC (Or EC10 /EC20) (mg/L)
406679-89-8	Silane, (isocyanatomethyl)dimethoxymethyl-	OECD 209	ASRI	1	2003	3 h	>1000
24801-88-5	Triethoxy(3-isocyanatopropyl)silane	OECD 209	ASRI	1	2013	3 h	180	NOEC 10, EC10 17, EC20 31 Heterotrophic inhibition of the respiration rate was comparable to the total inhibition

In the study with triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5), an activated sludge respiration inhibition 3-hour NOEC and EC10 values of 10 mg/L and 17 mg/L respectively were reported.

References:

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

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

PFA (2013ah). Peter Fisk Associates, STP Microorganism toxicity III-18 Analogue Group report, PFA.300.003.011