3-(triethoxysilyl)propanethiol

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

5 October 2020 - 8 October 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: all test concentrations and the control
- Sampling method: Samples were taken after preparation from one replicate at the start of the exposure. Then, 24 and 48 hour samples were taken from one additional replicate of each test item concentration and the control and analysed immediately. End samples were taken from pooled replicates and analysed immediately.
- Sample storage conditions before analysis: None

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Stock solution of 100 mg/l was prepared with diltuion water, stirred at 1100 rpm for one hour at room temperature. Test solutions were prepared by dilution of the stock solution with test media.
- Controls: same as dilution water (test media)
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): Stock solution was checked via laser beam (Tyndall effect) and no evidence of undissolved test item was found (negative).
- Other relevant information: none reported

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Strain: HINDAK CCAP 278/4
- Source (laboratory, culture collection): origin: Culture Collection of Algae and Protozoa (CCAP), SAMS Research Services Ltd, Dunstaffnage Marine Laboratory, Dunbeg, OBAN; Argyll PA37 1QA; Scotland, UK.
- Age of inoculum (at test initiation): 3 day old preculture
- Method of cultivation: Stocks were cultivated at the test facility using nutrient medium Z, fresh stocks were prepared monthly on Z-Agar.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

37 mg CaCO3/l

Test temperature:

22.5 - 23.5 degrees C

pH:

7.11 - 8.29

Dissolved oxygen:

not reported

Salinity:

not reported

Conductivity:

142 μS/cm

Nominal and measured concentrations:

Nominal: control, 1.0, 3.16, 10.0, 31.6, 100 mg/l
Measured: control, 0.319, 0.927, 4.84, 18.7 and 58.6 mg/l

Details on test conditions:

TEST SYSTEM
- Test vessel: sterile Erlenmeyer flasks, 250mL volume,
- Type (delete if not applicable): sealed with cotton wool plugs
- Material, size, headspace, fill volume: 100ml fill volume
- Aeration: test containers were placed on a rotary shaker and oscillated at approx. 70 rpm
- Initial cells density: 5375 cells/ml
- Control end cells density: 935596 cells/ml
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes - AAP medium (according to OECD guideline)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: ultrapure water (max conductivity was 0.1μS/cm)
- Total organic carbon: - Particulate matter: not reported
- Metals: not reported
- Pesticides: not reported
- Chlorine: not reported
- Alkalinity: 0.6 mmol/l. Acidity: 0.2 mmol/l
- Ca/mg ratio: not reported
- Conductivity: 142 μS/cm
- Culture medium different from test medium: no
- Intervals of water quality measurement: at the start of exposure and at the end of the exposure. Room temperature was continuously monitored and light intensity was measured prior to the start of the test.

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: culture media adjusted to pH 7.0 +/- 0.2
- Photoperiod: 24 hours light.
- Light intensity and quality: 4440-8880 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: fluorimeter
- Chlorophyll measurement: The cell density was measured daily via Chlorophyll a fluorescence, excitation at 436 nm, emission at 685 nm. Dilution water was used as a background signal. Self-fluorescence was observed in the preliminary range finding test at the concentration of 100 mg/L
- Other: Microscopic evaluation of the cells at the start and the end of the incubation period was carried out. The cells were checked for unusual cell shapes, colour differences, differences in chloroplast morphology, flocculation, adherence of algae to test containers and agglutination of algae cells.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: √10

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

32.2 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% C.I 27.4 - 40.1

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

11.8 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% C.I. 8.64-14.2

Duration:

72 h

Dose descriptor:

EC20

Effect conc.:

17.7 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% C.I. 16.1-19.2

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

4.84 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks:

and yield

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

18.7 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks:

and yield

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

13.4 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

other: yield

Remarks on result:

other: 95% C.I. 10.3 - 16.4

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

5.05 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

other: yield

Remarks on result:

other: 95% C.I. 3.04 - 8.15

Duration:

72 h

Dose descriptor:

EC20

Effect conc.:

7.19 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

other: yield

Remarks on result:

other: 95% C.I. 4.84-10.1

Details on results:

- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): Microscopic evaluation of the cells at the start and end of exposure revealed no morphological abnormalities.
- Any stimulation of growth found in any treatment: Yes, minor increase in growth rate in 0.927 and 0.319 mg/l treatments
- 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: no evidence reported

Results with reference substance (positive control):

ErC50 0.903 mg potassium dichromate/l (within the 0.775 +/- 0.558 mg/l range)
EyC50 0.441 mg/l (within the 0.421 +/- 0.339 mg/l range)

Reported statistics and error estimates:

Cell density from fluourescence, growth rate, growth rate inhibition, yield and yield inhibition were calculated according to OECD TG 201.
ECx values were determined by sigmoidal dose-response regression. NOEC and LOEC values were calculated using Dunnett's method with Shapiro-Wilk's normality test and Brown-Forsythe's equal variance tests conducted beforehand.

Table 1. Mean cell densities at daily intervals throughout the exposure period

TWA mean measured concentration (mg/l)	Mean cell density (cells/ml)
	0 hours	24 hours	48 hours	72 hours
58.6	5375	5648	5657	5527
18.7	5375	19670	67880	303162
4.84	5375	25624	152162	849232
0.927	5375	29022	190618	963663
0.319	5375	31079	191744	928897
Control	5375	32894	208323	935596

Table 2. Mean growth rate and yield after 72 hours' exposure

TWA mean measured concentrations (mg/l)	Mean growth rate (d^-1)	Inhibition of growth rate (%)	Yield (cells/ml)	Inhibition of yield (%)
58.6	0.0077	99	152	100
18.7	1.34	22	297787	68
4.84	1.69	2	843857	9
0.927	1.73	-1	958288	-3
0.319	1.71	0	923522	1
Control	1.72	-	930221	-

Table 3. Measured concentrations during the definitive test with algae

Nominal concentration (mg/l)	0 hours		24 hours		48 hours		72 hours		TWA mean measured concentration (mg/l)
	Meas. Conc. (mg/l)	%	Meas. Conc. (mg/l)	%	Meas. Conc. (mg/l)	%	Meas. Conc. (mg/l)	%
100	107	107	69.7	70	48.3	48	33.4	33	58.6
31.6	32.7	104	23.2	73	15.6	49	9.93	31	18.7
10.0	9.84	98	6.63	66	4.82	48	1.28	13	4.84
3.16	2.97	94	2.09	66	1.40	44	0.0292	<1	0.927
1.0	0.955	95	0.633	63	0.332	33	<LOQ	-	0.319
Control	<LOQ		<LOQ		<LOQ		<LOQ		-

LOQ = 0.05 mg/l of the test item

Validity criteria fulfilled:

yes

Remarks:

Control cultures increased by 174 fold (which is > 16 fold specified in the guideline), mean COV for each day in the controls was 11.8% (<35%) and COV of average specific growth rates was 1.41% in the controls (<7%)

Conclusions:

A 72-h ErC50 value of 32.2 mg/l, an ErC10 value of 11.8 mg/l and a NOEC of 4.84 mg/l have been determined for the effects of the test substance on growth rate of Pseudokirchneriella subcapitata, based on time weighted average measured concentrations of the parent substance. The test substance hydrolyses in water and based on the static exposure regime, it is likely that the test organisms were primarily exposed to a mixture of the parent and hydrolysis products of the substance. The ErC50, ErC10 and NOEC values are equivalent to 20.8, 7.6 and 3.1 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1995-07-03 to 1995-07-06

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 10, 20, 40, 80, 160, 319 and 639 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.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Seven nominal concentrations 10, 20, 40, 80, 160, 319 and 639 mg/L. 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.

- Controls: Dilution water (algal growth medium)

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM

- Strain: 86.81.SAG

- Source (laboratory, culture collection): Institute for Water, Ground and Air Hygiene, Berlin (Germany)

- Age of inoculum (at test initiation): 3 days

- Method of cultivation: A pre-culture is produced from an original culture by super-inoculation three days before the test begins. From this culture the test cultures are inoculated at a density of about 20000 cells/ml.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

not reported

Test temperature:

23.0 - 23.3 degrees C

pH:

8.2 - 8.7 at start of test

7.6 - 9.3 at end of test

Dissolved oxygen:

not reported

Salinity:

not applicable

Nominal and measured concentrations:

Nominal test concentrations: Control (0), 10, 20, 40, 80, 160, 319 and 639 mg/L.

Measured test concentrations at start of test: 0, 9.8, 19, 38, 76, 150, 332 and 596 mg/L.

Measured test concentrations at end of test: 0, 9.2, 19, 38, 73, 147, 296 and 577 mg/L.

The measured concentrations were with +/-20% of nominal. The results are therefore presented and interpreted with reference to nominal concentrations.

Details on test conditions:

TEST SYSTEM

- Test vessel: Erlenmeyer flasks

- Type: open

- Material, size, headspace, fill volume: glass

- Aeration: none

- Initial cells density: 1260000 cells/mL

- Control end cells density: 20000 cells/mL

- No. of vessels per concentration (replicates): 5

- No. of vessels per control (replicates): 8

GROWTH MEDIUM

- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS

- Culture medium different from test medium: no

- Intervals of water quality measurement: start and end of test

OTHER TEST CONDITIONS

- Sterile test conditions: yes

- Adjustment of pH: no

- Photoperiod: continuous

- Light intensity and quality: 8000 Lux

EFFECT PARAMETERS MEASURED:

- Determination of cell concentrations: spectrophotometer (absorption at 685 nm)

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

Reference substance (positive control):

no

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

931 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

growth rate

Remarks on result:

other: the concentration exceeds the highest treatment level in the test

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

267 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

92 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

36 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

40 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis products

Basis for effect:

growth rate

Details on results:

- Exponential growth in the control (for algal test): yes

Reported statistics and error estimates:

The area under the growth curve (biomass) and growth rate parameters were calculated from the cell concentration data in accordance with the description of the test method.

ECx values were determined by probit analysis (Cavalli-Sforza, 1972. Biometrie. Gustav Fischer Verlag, Stuttgart).

NOEC values were determined directly from the raw data.

Table 1. Results of analysis of test media

Nominal test substance concentration (mg/L)	Measured concentration at start of test (mg/L)	Measured concentration at end of test (mg/L)
0 (Control)	-	-
10	9.8	9.2
20	19	19
40	38	38
80	76	73
160	150	147
319	332	296
639	596	577

Table 2. Test results

Nominal test substance concentration (mg/L)	Mean cell concentration at start of test (cells/ml)	Mean cell concentration after 24 hours (cells/ml)	Mean cell concentration after 48 hours (cells/ml)	Mean cell concentration after 72 hours (cells/ml)
0 (Control)	20000	90000	350000	1260000
10	20000	80000	260000	1020000
20	20000	100000	350000	1290000
40	20000	90000	300000	1040000
80	20000	90000	310000	920000
160	20000	100000	270000	610000
319	20000	90000	200000	350000
639	20000	100000	170000	260000

Validity criteria fulfilled:

yes

Conclusions:

A 72-h ErC50 value of 931 mg/l, an ErC10 value of 92 mg/l and a NOEC of 40 mg/l have been determined for the effects of the test substance on growth rate of Desmodesmus subspicatus (reported as: Scenedesmus subspicatus) based on nominal concentrations of the substance. The test substance hydrolyses in water and it is therefore likely that the test organisms were primarily exposed to the hydrolysis products of the substance. These values are equivalent to 731, 72 and 31 mg/L when expressed in terms of the silanol hydrolysis product 3-(trihydroxysilyl)propanethiol.

Description of key information

Toxicity to aquatic algae: 72-hour E_rC₅₀ value 32.2 mg/l, E_rC₁₀ value 11.8 mg/l and NOE_rC 4.8 mg/l, for the effects of 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1) on growth rate of Pseudokirchneriella subcapitata, based on time weighted average measured concentrations of the substance, in an toxicity to aquatic algae test conducted in accordance with OECD TG 202 and in compliance with GLP (Noack 2020).

Key value for chemical safety assessment

EC50 for freshwater algae:

32.2 mg/L

EC10 or NOEC for freshwater algae:

11.8 mg/L

Additional information

Reliable 72-hour E_rC₅₀, E_rC₁₀, and NOE_rC values of 32.2 mg/l, 11.8 mg/l, 4.8 mg/l, respectively, have been determined for the effects of the registered substance, 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1), on the growth rate of Pseudokirchneriella subcapitata, based on time weighted average measured concentrations of the substance (Noack, 2020). Based on the static test regime, it is likely that the test organisms were exposed to a mixture of the parent and hydrolysis products of the substance. The study was conducted according to an appropriate test guideline 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) * (E_rC₅₀, E_rC₁₀ and NOE_rC of parent = 32.2, 11.8 and 4.8 mg/l, respectively) = 20.8, 7.6 and 3.1 mg/l.

A supporting 72-hour E_rC₅₀value of 931 mg/l, an E_rC₁₀value of 92 mg/l and a NOE_rC value of 40 mg/l have been determined for the effects of the read-across substance, 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0, EC No. 224-588-5) on the growth rate of Desmodesmus subspicatus (reported as: Scenedesmus subspicatus), based on nominal concentrations, conducted in accordance with EU Method C.3 (Algal Inhibition test) 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. These values are equivalent to 731, 72 and 31 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 is non-toxic to the environment and it is considered unlikely that its presence significantly affected the results of the test performed with the parent substance.

The supporting read-across data are 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.