3-(triethoxysilyl)propanethiol

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

7 October 2020 - 9 October 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations:
- Sampling method: All concentration levels and controls were sampled at the start of the exposure and at the renewal of the test solutions (0 and 24 hours), as well as in the 24 hours old media at 24 and 48 hours.
- Sample storage conditions before analysis: samples were stored in a freezer until the start of the analysis if necessary.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: a 10 mg test item/L stock solution was prepared in dilution water, stirred at 1100 rpm for 1 hour at room temperature. The stock solution was added to dilution water to prepare the test concentrations.
- Controls: same as dilution water (Elendt M4 media)
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): none reported
- Other relevant information:

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea
- Strain/clone: not reported
- Age at study initiation (mean and range, SD): <24 hours old
- Weight at study initiation (mean and range, SD): not reported
- Length at study initiation (length definition, mean, range and SD): not reported
- Source: Original stock source: Institut für Wasser-, Boden- und Lufthygiene (WaBoLu), 14195 Berlin, Germany. Bred at: Noack Laboratorien GmbH, Käthe-Paulus-Str. 1, 31157 Sarstedt, Germany
- Age of parental stock (mean and range, SD): not reported
- Feeding during test - daphnids were not fed during the study

ACCLIMATION
- Acclimation period: at least 2 hours in dilution water
- Acclimation conditions (same as test or not): same as test
- Health during acclimation (any mortality observed): not reported

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

255 - 265 mg CaCO3/L

Test temperature:

20.3 - 20.7 degrees C

pH:

6.90 - 7.43 in fresh media, 6.64 - 7.29 in 24 hour old media

Dissolved oxygen:

8.73 - 8.96 mg/L in fresh media, 8.00 - 8.60 in 24 hour old media

Salinity:

Not reported

Conductivity:

573 - 659 μS/cm

Nominal and measured concentrations:

Nominal: control, 0.625, 1.25, 2.5, 5.0, 10.0 mg/L
Geometric mean measured concentrations: control, 0.678, 0.960, 1.89, 3.89, 7.67 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass beakers 50mL capacity, loosely covered with watch glasses
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: glass, 7cm height x 4cm internal diameter
- Volume of solution: 20mL
- Aeration: not reported
- Renewal rate of test solution (frequency/flow rate): test solutions were renewed after 24 hours
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: same as culture medium (Elendt M4 medium)
- Total organic carbon: not reported
- Particulate matter: not reported
- Metals: not reported
- Pesticides: not reported
- Chlorine: not reported
- Alkalinity: not reported
- Ca/mg ratio: not reported
- Conductivity: not reported
- Salinity: not reported
- Culture medium different from test medium: no
- Intervals of water quality measurement: 0 and 24h

OTHER TEST CONDITIONS
- Adjustment of pH: culture medium was adjusted to pH 7.0 +/- 0.1
- Photoperiod: 16/8 hours light/dark cycle
- Light intensity: max 1500 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : immobilization was determined after 24 and 48 hours. Other adverse, sublethal effects (e.g. behaviur or appearance) was done but none occurred during the study

Reference substance (positive control):

yes

Remarks:

Potassium dichromate tested under static conditions.

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

2.71 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 95% C.I. 1.89 - 3.89 mg/L

Duration:

48 h

Dose descriptor:

EC10

Effect conc.:

2.03 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 95% C.I. 1.89 - < 3.89

Duration:

48 h

Dose descriptor:

EC100

Effect conc.:

3.89 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

3.79 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 95% C.I. 1.98 - 7.15

Duration:

24 h

Dose descriptor:

EC10

Effect conc.:

3.52 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 1.88 - 6.97

Duration:

24 h

Dose descriptor:

EC100

Effect conc.:

> 7.67 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

- Behavioural abnormalities: behaviour was monitored, but no abnormalities observed
- Other biological observations: appearance was monitored, but no abnormalities observed.
- Mortality of control: 0%
- Immobilisation of control: 0%
- Abnormal responses: observed, but none recorded
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: none
- Effect concentrations exceeding solubility of substance in test medium; not reported

Results with reference substance (positive control):

EC50 = 2.03 mg potassium dichromate/L, which is within the 0.6 - 2.4 mg/l range according to AQS P 9/2 (02/2000)

Reported statistics and error estimates:

EC values were calculated using sigmoidal dose-response regression with GraphPad Prism. 95% confidence intervals were calculated from the standard error and t-distribution.

Table 1. Immobilization rates after 24 and 48 hours of exposure

Geometric mean measured concentration (mg/l)	Immobilization after 24h					Immobilization after 48 hours
	1	2	3	4	Mean	1	2	3	4	Mean
7.67	80	100	100	60	85	100	100	100	100	100
3.89	80	80	60	40	65	100	100	100	100	100
1.89	0	0	0	0	0	0	0	0	0	0
0.960	0	0	0	0	0	0	0	0	0	0
0.678	0	0	0	0	0	0	0	0	0	0
Control	0	0	0	0	0	0	0	0	0	0

Table 2. Absolute numbers of immobile Daphnids after 24 and 48 hours of exposure.

Geometric mean measured concentration (mg/l)	Number of immobile daphnids after 24h					Number of immobile daphnids after 24h
	1	2	3	4	Sum	1	2	3	4	Sum
7.67	4/5	5/5	5/5	3/5	17/20	5/5	5/5	5/5	5/5	20/20
3.89	4/5	4/5	3/5	2/5	13/20	5/5	5/5	5/5	5/5	20/20
1.89	0/5	0/5	0/5	0/5	0/20	0/5	0/5	0/5	0/5	0/20
0.960	0/5	0/5	0/5	0/5	0/20	0/5	0/5	0/5	0/5	0/20
0.678	0/5	0/5	0/5	0/5	0/20	0/5	0/5	0/5	0/5	0/20
Control	0/5	0/5	0/5	0/5	0/20	0/5	0/5	0/5	0/5	0/20

Table 3. Nominal and geometric mean measured concentrations of the test substance throughout the exposure

Nominal test concentration (mg/l)	Fresh media, 0 hours		Old media, 24 hours		Fresh media, 24 hours		Old media, 48 hours		Geometric mean measured concentration (mg/L)
	Measured conc. (mg/l)	% of nominal	Measured conc. (mg/l)	% of nominal	Measured conc. (mg/l)	% of nominal	Measured conc. (mg/l)	% of nominal
10.0	9.75	98	6.24	62	10.3	103	5.51	55	7.67
2.0	5.02	100	2.82	56	5.15	103	3.12	62	3.89
2.5	2.50	100	1.32	53	2.55	102	1.51	60	1.89
1.25	1.20	96	0.742	59	1.25	100	0.763	61	0.960
0.625	0.609	97	0.377	60	1.26	202	0.729	117	0.678
Control	<LOQ		<LOQ		<LOQ		<LOQ		<LOQ

Validity criteria fulfilled:

yes

Remarks:

0% mortality in the controls and >= 8.00 mg O2/L, therefore meeting the OECD 202 validity criteria (<= 10% mortality and >= 3 mg O2/L respectively).

Conclusions:

A 48-h EC50 value of 2.71 mg/l and an EC10 value of 2.03 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna based on geometric mean measured concentrations of the substance. Based on the semi-static test regime, it is likely that the test organisms were exposed to the parent substance, therefore the values have been reported in terms of the parent substance, 3-(triethoxysilyl)propanethiol. The EC50 is equivalent to 1.75 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Reference 2

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1995-09-26 to 1995-09-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 0.64, 1.3, 2.7, 5.4, 11, 21 and 43 mg/l and the fresh stock solution used to prepare the test media.

- Sampling method: Concentrations of test substance hydrolysis products determined in fresh media at all concentrations after preparation and again before renewal after 24 hours. The concentrations of the fresh stock solution used to prepare the test media was also determined.

- Sample storage conditions before analysis: not reported

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Test media prepared by dilution of a 1000 mg/l stock solution prepared by mixing for 18 h followed by filtration. TOC concentration of stock solution determined and used as the basis for determining the nominal test concentrations.

- Test concentrations (Nominal): Control, 0.64, 1.3, 2.7, 5.4, 11, 21 and 43 mg/l

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Common name: Daphnia magna

- Strain: Clone 5

- Source: Stock culture

- Age at study initiation (mean and range, SD): <24 h

- Method of breeding: Parthenogenetic reproduction

- Feeding during test: None

ACCLIMATION

- Acclimation conditions (same as test or not): yes

- Type and amount of food: sufficient to be consumed each day leaving no residue

- Feeding frequency: daily

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

The sum of the Ca2+ and Mg2+ ions: 2.5 mmol

Test temperature:

20 +/-1 degree C

pH:

7.5 - 7.9

Dissolved oxygen:

8.8 - 9.6 mg/l

Salinity:

not applicable

Nominal and measured concentrations:

- Test concentrations (Nominal): Control, 0.64, 1.3, 2.7, 5.4, 11, 21 and 43 mg/l

- Test concentrations (at start of test): Control,
- Test concentrations at end of test: Control,
- The measured concentrations that were >LOD were within +/-20% of nominal. The results are therefore presented and interpreted with reference to nominal concentrations.

Details on test conditions:

TEST SYSTEM

- Test vessel: glass cylinder

- Type: open

- Material, size, headspace, fill volume: cylinder containing 10 ml of test medium

- Aeration: none

- No. of organisms per vessel: 5

- No. of vessels per concentration (replicates): 4

- No. of vessels per control (replicates): 4


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Elendt M4 medium

- Intervals of water quality measurement: end of test


OTHER TEST CONDITIONS

- Photoperiod: Dark


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Immobilization after 24 and 48 h exposure


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

6.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mobility

Remarks on result:

other: 4.9 - 9.1

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

20 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mobility

Remarks on result:

other: 12 - 36

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

2.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mobility

Results with reference substance (positive control):

- Results with reference substance valid?

- EC50/LC50: >1 mg/l, <2.0 mg/l

Reported statistics and error estimates:

EC50 and confidence interval determined by Probit analysis

Table 1. Results of analysis of test media

Nominal test concentration (mg/l)	Measured concentration at start of test (mg/l)	Measured concentration at end of test (mg/l)
0 (Control)	-	-
0.64	<LOD	<LOD
1.3	<LOD	<LOD
2.7	Unreliable value	2.3
5.4	Unreliable value	6.3
11	12.4	9.7
21	20.9	20.4
43	37.7	39.8

Table 2. Test results

Nominal test concentration (mg/l)	Mean percentage immobilisation after 24 hours	Mean percentage immobilisation after 48 hours
0 (Control)	5	5
0.64	0	0
1.3	0	0
2.7	0	5
5.4	15	50
11	50	85
21	40	90
43	70	95

Validity criteria fulfilled:

yes

Conclusions:

A 48-h EC50 value of 6.7 mg/l and a NOEC of 2.7 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna based on nominal concentrations of the substance. The test substance is susceptible to hydrolysis and it is therefore likely that the test organisms were primarily exposed to the hydrolysis products of the substance. The EC50 is equivalent to 5.3 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Description of key information

Short-term toxicity to aquatic invertebrates: 48-hour EC50 value 2.71 mg/l for the effects of 3-(triethoxysilyl)propanethiol on the mobility of Daphnia magna, based on geometric mean measured concentrations of the substance. The EC50 is equivalent to 1.75 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

2.71 mg/L

Additional information

A reliable 48-hour EC₅₀ value of 2.71 mg/l and a reliable EC₁₀ value of 2.03 mg/l have been determined for the effects of 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1) on mobility of Daphnia magna based on geometric mean measured concentrations of the substance. A 48-hour EC₁₀₀ value of 3.89 mg/l, based on geometric mean measured concentrations was also determined in this test. Due to the semi-static test procedure, the test organisms were exposed largely to the parent substance. The values have been reported as mean measured concentrations, which reflect the concentration of the parent substance, 3-(triethoxysilyl)propanethiol (CAS 14814-09-6). The measured concentrations indicate that approximately 50-60% of the parent substance was present after each 24-hour renewal period; this loss is assumed to be due to hydrolysis, therefore, there is also some exposure to the hydrolysis product. The study was conducted in accordance with OECD TG 202 and in compliance with GLP and was assigned a reliability score of 1.

The results may be expressed in terms of the concentration of the hydrolysis product, by applying a molecular weight correction (MW of silanol = 154.26 / MW of parent = 238.42) * (EC₅₀ of parent = 2.71 mg/l) = 1.75 mg/l.

A supporting 48-hour EC₅₀ value of 6.7 mg/l has been read-across for the effects of the read-across substance 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0, EC No. 224-588-5), conducted in accordance with EU Method C.2 (Acute Toxicity for Daphnia) and in compliance with GLP (Hüls 1995) on mobility inDaphnia magna. In view of hydrolysis half-life of the read-across parent substance (2.6 hours at pH 7 and 20-25°C (QSAR)), it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The EC₅₀ is equivalent to 5.3 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

The read-across substance, 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0), and the registration substance, 3-(triethoxysilyl)propanethiol (CAS 14814-09-6), both hydrolyse to the same hydrolysis product, 3-(trihydroxysilyl)propanethiol. Both substances have hydrolysis half-lives which indicate that, under conditions relevant to ecotoxicity assessment, both will partially hydrolyse to 3-(trihydroxysilyl)propanethiol over the course of a static test.

The other hydrolysis products are ethanol and methanol respectively; the properties of these substances are well characterised. Methanol and ethanol are non-toxic to the environment and it is considered unlikely that their presence would significantly affect the results of tests performed with the either the registered or read-across substance.

The supporting read-across study is included to demonstrate that the substance is significantly more toxic to Daphnia than to fish and to assess the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol. Both the registered substance and the read-across substance contain a thiol (SH) group and both hydrolyse to 3-(trihydroxysilyl)propanethiol, which also contains the thiol group. The thiol group is a structural alert associated with enhanced toxicity in Daphnia (ECHA Guidance Chapter R.10) and is believed to drive the toxicity of the substance. ECHA guidance Chapter R.7b states that if there is compelling evidence to suggest that the fish value is likely to be at least a factor of about 10 less sensitive than invertebrates or algae there are no further requirements for fish testing. Because, in the interest of animal welfare, the short-term toxicity to fish test conducted with the registered substance was a threshold toxicity test, it is not possible to compare relative sensitivities of the test species. The inclusion of the read-across data allows for comparison of species sensitivity. The data demonstrate that the fish are more than a factor of 10 less sensitive than invertebrates.