3-(triethoxysilyl)propanethiol

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key 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 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-mercaptopropylsilanetriol.

Description of key information

A 72-hour ErC₅₀ value of 931 mg/l, an ErC₁₀ value of 92 mg/L and a NOErC 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) on the growth rate of Desmodesmus subspicatus, based on nominal concentrations. These values are equivalent to 731, 72 and 31 mg/L when expressed in terms of the silanol hydrolysis product 3-(trihydroxysilyl)propanethiol.

A stepwise testing strategy is proposed to address the requirements of the ECHA decision letter (TPE-D-2114432420-65-01/F). Please refer to the attachment in IUCLID Section 13. This read-across is retained as an interim measure to calculate a PNEC and support the existing chemical safety assessment until new evidence becomes available.

Key value for chemical safety assessment

EC50 for freshwater algae:

931 mg/L

EC10 or NOEC for freshwater algae:

40 mg/L

Additional information

There are no reliable algal toxicity data available for 3-(triethoxysilyl)propanethiol (CAS 14814-09-6), therefore good quality data for an appropriate structural analogue, 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) have been read across. 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 the 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.

 

A 72-hour ErC₅₀ value of 931 mg/L, an ErC₁₀ value of 92 mg/L and a NOErC value of 40 mg/L have been determined for the effects of 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) on the growth rate of Desmodesmus subscpicatus based on nominal concentrations of the substance (Hüls, 1995). The result was obtained under static test conditions. In view of the test media preparation method and exposure regime, it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance.

The results may be expressed in terms of the concentration of the hydrolysis product, 3-(trihydroxysilyl)propanethiol, by applying a molecular weight correction (MW of silanol = 154.26/ MW of parent = 196.34) * (concentration of parent = 931, 92 and 40 mg/L) = 731, 72 and 31 mg/L.

The study was considered to be reliability 1 (reliable without restrictions)