3-(triethoxysilyl)propanethiol

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18 January 2021 - 22 January 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Deviations:

no

Principles of method if other than guideline:

In order to avoid the unnecessary use of animals, the threshold approach for fish toxicity testing was employed. In accordance with OECD Guidance document No. 126, the nominal limit test concentration for this study was selected from the lowest EC50 value from the short-term invertebrate and algal tests (see IUCLID sections 6.1.3 and 6.1.5, respectively). Because no toxicity was observed at this concentration (96-hour LC50 > 2.55 mg/l), this indicates that fish are not the most sensitive trophic level and a full OECD TG 203 study is not required.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations:
- Sampling method: Samples were taken at 0 and 72 hours (fresh media) and 24 and 96 hours (24 hour aged media).
- Sample storage conditions before analysis: Samples were frozen in a refrigerator until analysis.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Test item was weighed and transferred into a test vessel with an appropriate amount of the dilution water and adjusted to pH 7 (+/- 0.1). Test media was stirred with a magnetic stirrer at 1100 rpm for 1 hour.
- Controls: dilution water without test item but from the same age and source as the test material solutions
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): None reported

Test organisms (species):

Danio rerio (previous name: Brachydanio rerio)

Details on test organisms:

TEST ORGANISM
- Common name: Zebrafish
- Strain: Not reported
- Source: gained at test facility from a single brood stock (supplier: Umweltbundesamt, Schichauweg 58, D-12307 Berlin)
- Age at study initiation (mean and range, SD): Juvenile
- Length at study initiation (length definition, mean, range and SD): Initiation values not reported, however average body length at study end was 1.80cm
- Weight at study initiation (mean and range, SD):Initiation values not reported, however average body weight at study end was 0.056g
- Method of breeding: not reported
- Maintenance of the brood fish: holding of stock was performed in accordance with laboratory SOPs Water changed at least once per week, DO was >80% air saturation value

ACCLIMATION
- Acclimation period: 9 days
- Acclimation conditions (same as test or not): Same as test conditions
- Type and amount of food during acclimation: Sera Vipan food. Amount was 4% of fish body weight per feeding day.
- Feeding frequency during acclimation: food provided 3 times per week and given to satiation per feeding day. Test fish were not fed 24h before test start
- Health during acclimation (any mortality observed): no mortality observed


FEEDING DURING TEST - fish not fed during test

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

96 h

Hardness:

66 mg/L total hardness

Test temperature:

23.0 - 23.9 degrees C

pH:

7.05 - 7.95

Dissolved oxygen:

84 - 100% oxygen saturation

Salinity:

Not reported

Conductivity:

Not reported

Nominal and measured concentrations:

Nominal: control and 4 mg/L
Measured: control (

Details on test conditions:

TEST SYSTEM
- Test vessel: glass 3L aquaria
- Type (delete if not applicable): open (covered with glass plates)
- Material, size, headspace, fill volume: 2.5 L per vessel
- Aeration: no aeration provided
- Renewal rate of test solution (frequency/flow rate): test media renewed at 72 hours
- No. of organisms per vessel: 7 fish per concentration and 7 for the control
- No. of vessels per concentration (replicates):1
- No. of vessels per control (replicates): 1
- Biomass loading rate: 0.157 g fish per liter test solution

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: same used as holding - tap water of local origin. Water was filtered on activated charcoal and aerated for at least 24 hours to remove chlorine
- Total organic carbon: <2 mg/L
- Particulate matter: not reported
- Metals: not reported
- Pesticides: not reported
- Chlorine: < 0.01 mg/L
- Alkalinity: not reported
- Ca/mg ratio: not reported
- Culture medium different from test medium: no
- Intervals of water quality measurement: pH, temperature and oxygen saturation were measured in all test vessels daily, chlorine and nitrate were measured from each batch of dilution water used in the test. Hardness was determined at the start of the exposure, TOC was sampled at the start of the exposure and frozen until analysis. Water temperature was continuously recorded.

OTHER TEST CONDITIONS
- Adjustment of pH: New test solutions (0 and 72h renewals) were adjusted to 7.0 +/- 0.1 before and after application of the test item
- Photoperiod: 16h / 8h light dark cycle
- Light intensity: 540 - 1000 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : observations were made after 2+/- 0.5h and 5 +/- 1h after the start of the exposure. On days 1-4 of the test, all vessels with living fish were inspected twice per day. Measurements of fish weight and size were conducted at the end of the exposure. Fish were considered dead if there was no visible movement (e.g. gill covers movement) and if touching of the caudal peduncle produced no reaction. Records were kept of visible abnormalities (e.g. loss of equilibrium, swimming behavior, respiratory function, pigmentation, etc.).

TEST CONCENTRATIONS
- Justification for using less concentrations than requested by guideline: limit test

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

LC0

Effect conc.:

>= 2.55 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 2.55 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

- Behavioural abnormalities:
- Observations on body length and weight: Average body length at end of test = 1.80 cm, average body weight at end of test = 0.056 g
- Other biological observations: behaviour was monitored but no abnormalities to equilirbium, appearance, swimming behaviour, ventilatory behaviour were observed
- Mortality of control: 0%
- Abnormal responses: No abnormalities to behaviour or fish appearance were observed
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: none reported
- Effect concentrations exceeding solubility of substance in test medium: none reported

Reported statistics and error estimates:

No effects were observed so statistical analysis was not conducted

Sublethal observations / clinical signs:

Table 1. Observations of sub lethal effects and normal behaviour in the test vessels

Nominal test item concentration (mg/L)	Number of fish affected at observation time (hours)
	Day 0		Day 1		Day 2		Day 3		Day 4
	2	5	22	29	46	53	70	78	94	96
Control	7	7	7	7	7	7	7	7	7	7
4.00	7	7	7	7	7	7	7	7	7	7

Table 2. Measured concentrations of the test item during the definitive test

Sampling date	Fresh media, 0 hours		Old media, 24 hours		Fresh media, 72 hours		Old media, 96 hours
Nominal test item concentration (mg/L)	Measured concentration (mg/L)	%	Measured concentration (mg/L)	%	Measured concentration (mg/L)	%	Measured concentration (mg/L)	%
Control	<LOQ		<LOQ		<LOQ		<LOQ
4.00	3.33	83	1.83	46	3.46	86	2.01	2.55
Geometric mean measured concentration for the test concentration = 2.55 mg/L

Validity criteria fulfilled:

yes

Remarks:

O2 saturation remained above 60% (>=84%), 0% mortality was observed in the control group, analytical measurement of the test concentrations were conducted

Conclusions:

A 96-h LC50 value of >2.55 mg/l and an LC0 of ≥2.55 mg/l have been deternined for the effects of the test substance on mortality of Danio rerio based on geometric mean measured concentrations of the substance. In light of the semi-static test procedure, it is likely that the test organisms were exposed to the parent substance, therefore values have been reported in terms of the parent substance, 3-(triethoxysilyl)propanethiol. The LC50 is equivalent to >1.65 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Reference 2

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1995-07-31 to 1995-08-04

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.1 (Acute Toxicity for Fish)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 100, 180, 350, 550 and 1000 mg/l and the fresh stock solutions 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 solutions 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. Stock solutions were prepared by stirring for 18 h followed by filtration. TOC concentration of stock solution determined and used as the basis for determining the nominal test concentrations.

- Differential loading: Five nominal test concentrations 100, 180, 350, 550 and 1000 mg/l

- Controls: Dilution water

Test organisms (species):

Danio rerio (previous name: Brachydanio rerio)

Details on test organisms:

TEST ORGANISM

- Common name: Zebrafish

- Source: West aquarium, Bad Lauterberg, Germany

- Length at study initiation (length definition, mean, range and SD): 3.0 cm +/-0.5 cm

- Feeding during test: none

ACCLIMATION

- Acclimation period: at least 14 days

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

- Type and amount of food: TetraMin® at 1% of body weight

- Feeding frequency: Daily

- Health during acclimation (any mortality observed): The fish exhibit normal behaviour and are free from visible signs of disease at the start of the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

≈ 12ºdH

Test temperature:

20 - 22ºC

pH:

8.0 - 8.4

Dissolved oxygen:

84 - 111%

Salinity:

not applicable

Nominal and measured concentrations:

Nominal concentrations: 100, 180, 350, 550 and 1000 mg/l.

Initial measured concentrations: 100, 157, 334, 502 and 1005 mg/l.

Concentrations in media prior to replacement after 24 hours: 109, 156, 327, 514 and 929 mg/l.

Geometric mean measured concentrations (0-24h): 104, 156, 330, 508 and 968 mg/l.

The test results are presented and interpreted with reference to nominal concentrations.

Details on test conditions:

TEST SYSTEM

- Test vessel:

- Type (delete if not applicable): open aquarium

- Material, size, headspace, fill volume: 20 litres

- Aeration: Continuous

- Renewal rate of test solution (frequency/flow rate): Daily

- No. of organisms per vessel: 10

- No. of vessels per concentration (replicates): 1

- No. of vessels per control (replicates): 1

- Biomass loading rate: 0.49 g/l


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Potable water from Gelsenwasser AG


OTHER TEST CONDITIONS

- Adjustment of pH: None

- Photoperiod: 16 h light/8 h dark


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Mortality after 24, 48, 72 and 96 h


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 1.8

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

350 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mortality (fish)

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

439 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mortality (fish)

Remarks on result:

other: Concentrations bounding LC50: 350 - 550 mg/l

Duration:

72 h

Dose descriptor:

LC50

Effect conc.:

451 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mortality (fish)

Duration:

48 h

Dose descriptor:

LC50

Effect conc.:

486 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mortality (fish)

Duration:

24 h

Dose descriptor:

LC50

Effect conc.:

742 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

mortality (fish)

Details on results:

- Mortality of control: Zero

Reported statistics and error estimates:

LC50 determined by graphical interpolation

Sublethal observations / clinical signs:

Table 1. Test results

Nominal test substance concentration (mg/l)	Percentage mortality after 24 hours	Percentage mortality after 48 hours	Percentage mortality after 72 hours	Percentage mortality after 96 hours
0 (Control)	0	0	0	0
100	0	0	0	0
180	0	0	0	0
350	0	0	0	0
550	0	70	90	100
1000	100	100	100	100

Validity criteria fulfilled:

yes

Conclusions:

A 96-h LC50 value of 439 mg/l and NOEC of 350 mg/l have been deternined for the effects of the test substance on mortality of Brachydanio rerio 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 LC50 is equivalent to 345 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Description of key information

Short-term toxicity to fish: 96-hour LC₅₀ >2.55 mg/l for the effects of 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1) on the mortality ofDanio reriobased on geometric mean measured concentrations of the substance in a fish toxicity test in accordance with the OECD TG 203 Threshold Approach for Acute Fish Toxicity Testing and in compliance with GLP (Noack 2021). The LC₅₀is equivalent to >1.65 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

LC50

Effect concentration:

> 2.55 mg/L

Additional information

A reliable 96-hour LC₅₀ value of >2.55 mg/l and a reliable LC₀ of ≥2.55 mg/l have been determined for the effects of 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1) on mortality of Danio rerio based on geometric mean measured concentrations of the substance (Noack, 2021). In light of the semi-static test procedure, it is likely that 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% 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 products. The study was conducted in accordance with the OECD TG 203 Threshold Approach for Acute Fish Toxicity Testing 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) * (LC₅₀of parent = >2.55 mg/l) = >1.65 mg/l.

A supporting 96-hour LC₅₀ value of 439 mg/l has been reported for the effects of the read-across substance, 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0, EC No. 224-588-5), on the mortality of Brachydanio rerio (new name: Danio rerio), conducted in accordance with EU Method C.1 (Acute Toxicity for Fish) and in compliance with GLP (Hüls 1995). 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 LC₅₀ is equivalent to 345 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 registered 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 less toxic to fish than to Daphnia 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.