Decyltrimethoxysilane

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:

From December 2017 to March 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Remarks:

0.3°C under required temperature range, deemed to have no effect on the outcome.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata; Raphidocelis subcapitata; Selenastrum capricornutum
- Strain: CCAP 278/4.
- Source (laboratory, culture collection): Culture Collection of Algae and Protozoa, SAMS Ltd
- Method of cultivation: In a 250 ml conical flask: temperature: 21.0 – 21.6°C; Illumination: 6220 - 7980 lux continuous white light; Orbiting: set to 200 rpm.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Remarks on exposure duration:

72 h total exposure duration, observations made at 24, 48 and 72 h.

Test temperature:

20.7 – 22.8°C

pH:

Initial pH: 8.04
During test: 7.91 – 8.59

Nominal and measured concentrations:

Nominal concentrations (preliminary tests): 0.1, 1.0, 10 and 100 mg/L
Nominal concentrations (definitive limit test): 0 and 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: flask
- Type: Conical (Not specified if open or closed)
- Material, size, headspace, fill volume: 250 mL capacity
- Initial cells density: 1 x 10^4 cells/mL
- Control end cells density: 3.3 cells/mL x 10^4 (24 h), 14.2 cells/mL x 10^4 (48 h), 51.1 cells/mL x 10^4 (72 h),
- No. of organisms per vessel: 3.3-3.8 cells/mL x 10^4 (test initiation average)
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: Sterilised deionised water with added nutrients according to the OECD 201 standard.

WATER PARAMETERS
- Source/preparation of dilution water: Deionised water
- Total organic carbon: None
- Particulate matter: None
- Metals: None
- Pesticides: None
- Chlorine: None
- Alkalinity: None
- Ca/mg ratio: None
- Conductivity: None
- Culture medium different from test medium: No
- Intervals of water quality measurement: 0, 24, 48 and 72 h

OTHER TEST CONDITIONS
- Adjustment of pH: no, pH of media before test measured at pH 8.04
- Photoperiod: continuous
- Light intensity and quality: 6220 - 7980 lux, white light

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- Determination of cell concentrations: Cell densities were measured microscopically by direct cell counts at 24, 48 and 72 h ((+-) 2 h) timepoints using a haemocytometer and microscope.
- Chlorophyll measurement: estimated graphically, calculated using ToxCalc™ (Version 5.0) “Comprehensive Toxicity Data Analysis and Database Software”

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 100 mg/L spacing.
- Justification for using less concentrations than requested by guideline: None specified
- Range finding study: Yes, 0.1, 1, 10 and 100mg/L of test substances used
- Test concentrations: Definitive limit test: 0, 100 mg/L
- Results used to determine the conditions for the definitive study: Yes

Reference substance (positive control):

yes

Remarks:

A separate reference study was used (ENV 11396) using potassium dichromate to check the test procedure and sensitivity of the test species.

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other:

Remarks:

Yield

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

- Exponential growth in the control (for algal test): yes (logarithmic growth)
- Observation of abnormalities (for algal test): No
- Unusual cell shape: No
- Colour differences: Conical flask appear clear at 24 h, slightly green at 48 h and green at 72 h (Same for control and test substance).
- Flocculation: None specified
- Adherence to test vessels: None specified
- Aggregation of algal cells: None specified
- Other: None specified
- Any stimulation of growth found in any treatment: No
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Dissolved concentrations likely to be lower than stated as Decyltrimethoxysilane was not soluble in water (it hydrolyses very slowly with water)
- Effect concentrations exceeding solubility of substance in test medium: No

Results with reference substance (positive control):

Potassium dichromate (ENV 11396), ErC50 obtained was 1.06 mg/L

Reported statistics and error estimates:

Where possible, EC50 was estimated (graphically, 95% confidence limits) according to ToxCalc (Version 5.0), “Comprehensive Toxicity Data Analysis and Database Software”.

Validity criteria fulfilled:

yes

Conclusions:

The 72 hour EC(r)50 was >100 mg/l (determined by Linear Interpolation).
The 72 hour EC(y)50 was >100 mg/l (determined by Linear Interpolation).
The 0 to 72-hour NOEC(r) was >100 mg/l (determined by Homoscedastic t Test).
The 0-72 hour LOEC was >100mg/l (determined by Homoscedastic t Test).

Executive summary:

The short-term toxicity of Decyltrimethoxysilane to Pseudokirchneriella subcapitata was determined during a GLP-compliant study performed according to the OECD Testing Guideline 201. A range-finding test was performed to determine the concentrations to be used during the definitive test. As a result of this range-finding test, a limit test was performed with 100 mg/L of Decyltrimethoxysilane.

The 72-hour EC50 was >100 mg/L under the conditions of the test.

Description of key information

The short-term toxicity of Decyltrimethoxysilane to Pseudokirchneriella subcapitata was determined during a GLP-compliant study performed according to the OECD Testing Guideline 201. A range-finding test was performed to determine the concentrations to be used during the definitive test. As a result of this range-finding test, a limit test was performed with 100 mg/L of Decyltrimethoxysilane.

The 72-hour EC50 was >100 mg/L under the conditions of the test.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L