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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1994-05-10 to 1994-05-13
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP, and was considered to be reliability 1 (reliable without restrictions).
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: 500 mg/l nominal treatment

- Sampling method: Samples of test media were taken at the start and end of the test

- Sample storage conditions before analysis: Refrigerated
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 500 mg/l nominal concentration of the test substance was prepared by stirring overnight.

- Controls: Dilution water (algal growth medium)
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM

- Strain: CCAP 278/4

- Source (laboratory, culture collection): Culture Collection of Algae and Protozoa (CCAP), Institute of Freshwater Ecology, Ambleside, Cumbria, U.K.

- Age of inoculum (at test initiation): Cultures in exponential growth

- Method of cultivation: Axenic cultures maitained in liquid medium.


ACCLIMATION

- Acclimation period:

- Culturing media and conditions: same as test
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Hardness:
no data
Test temperature:
24ºC
pH:
Control: 7.9 - 9.6

500 mg/l treatment: 7.9 - 9.3
Dissolved oxygen:
no data
Salinity:
not applicable
Nominal and measured concentrations:
Nominal concentration: 500 mg/l

Measured concentration at start of test: 486 mg/l

Measured concentration at end of test: 508 mg/l

Mean measured concentration: 497 mg/l

Mean measured concentration as a % of nominal: 99.4

The test results are presented and interpreted with reference to nominal concentrations.
Details on test conditions:
TEST SYSTEM

- Test vessel: Erlenmeyer flasks

- Type: closed

- Material, size, headspace, fill volume: Glass, 250 ml, no headspace, full

- Aeration: no

- Renewal rate of test solution (frequency/flow rate): no

- Initial cells density: 10000 cells/ml

- Control end cells density: ˜250000 cells/ml

- No. of vessels per concentration (replicates): 3

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


GROWTH MEDIUM

- Standard medium used: yes


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Standard algal growth medium in accordance with EU test method

- Culture medium different from test medium: no


OTHER TEST CONDITIONS

- Sterile test conditions: yes

- Adjustment of pH: no

- Photoperiod: Continuous

- Light intensity and quality: 12527 - 11745 Lux


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

- Determination of cell concentrations: electronic particle counter
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 500 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 500 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 500 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 500 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
biomass
Details on results:
- Exponential growth in the control (for algal test): yes

- Any stimulation of growth found in any treatment: no
Reported statistics and error estimates:
No toxic effects were observed in the test media, the test results were therefore not subject to statistical analysis.
Validity criteria fulfilled:
yes
Conclusions:
(72-hour) EC50: >500 mg/l growth rate of Pseudokirchnerella subcapitata, reliability based on nominal concentration of the substance. However it is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.
Executive summary:

There are no data for the registered substance. However a 72 EC50 value of >3.6 mg/l and NOEC of =3.6 mg/l have been determined for the effects of the read-across substance, trimethoxy(methyl)silane (CAS 1185 -55 -3), on growth rate of Pseudokirchnerella subcapitata based on geometric mean measured exposure concentrations of the test substance. The test substance is known to hydrolyse rapidly in water and 3.6 mg/l was the concentration measured in the highest nominal test concentration of 120 mg/l. It is therefore likely that the test organisms were predominantly exposed to the hydrolysis products of the substance.

A 72-hour EC50 value of >500 mg/l and NOEC of =500 mg/l have also been determined for the effects of a second read-across substance, triethoxy(methyl)silane (CAS 2031 -67 -6), on growth rate of Pseudokirchnerella subcapitata (tested as: Selenastrum capricornutum) based on nominal concentration of the substance. It is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2007-04-16 to 2007-05-10
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP, and was considered to be reliability 1 (reliable without restrictions).
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
- Sampling method: Test Concentrations were measured in each  treatment at test initiation and at test termination
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method:   Stock solutions were prepared by direct addition of test article to algal  assay medium
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
- Species/strain # and source: Pseudokirchneriella subcapitata/Strain UTEX 1648,  from in-house cultures initiated from cultures originally supplied by the University of Texas at Austin.

- Initial Density 10,000 cells/ml
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
Not reported
Test temperature:
24.0 to 24.4ºC
pH:
7.6-7.7 at start of test

7.8-9.0 at end of test
Dissolved oxygen:
Not reported
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: Negative Control, 7.5, 15, 30, 60 and 120 mg/l

Mean measured concentrations:
The large difference between nominal and mean measured exposure concentrations is attributed to the hydrolysis of the test substance under the static test conditions. The hydrolysis half-life of  methyltrimethoxysilane is approximately 2.2 hours.  All measured  concentrations on Day 3 were less than the limit of quantitation (LOQ =  0.27 mg/l).  Due to the decline in test concentrations during the test,  mean measured concentrations were estimated as the geometric mean of Day  0 and Day 3 measured concentrations.  The geometric mean concentrations  were calculated using ½  LOQ for all Day 3 measurements (0.135 mg./l).
Details on test conditions:
TEST SYSTEM

- Exposure vessel type:  250-ml Erlenmeyer flasks covered with a sponge  closure containing 100-ml of test solution.

- Test Design:  Three replicates for each treatment group.  Five test  concentrations and a negative control.

- Element basis (i.e. number of cells/ml, area under the curve, growth  rate, etc.): Yield (Biomass) and Growth Rate "  

- Growth/test medium chemistry:  Algal Assay Medium (ASTM E 1218-04), pH  7.6

- Dilution water source:  Distilled Water

- Water chemistry in test:  Temperature was measured in the environmental  chamber daily.  Measurements of pH were made in each treatment group at  test initiation and test termination.

- Light levels and quality during exposure:  490 to 626 foot-candles,  continuous cool-white fluorescent lighting
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 120 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Growth Rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 120 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Yield (Biomass) and Growth Rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 3.6 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: Growth Rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 3.6 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: Yield (Biomass) and Growth Rate
Details on results:
- Exponential growth in the control (for algal test): yes

- Observations:  Visual examination of algal cells at test termination showed no concentration-dependent changes in shape, color or size.
Reported statistics and error estimates:
Statistical methods: Dunnett's test was used to determine if there were differences between Control and treatments.

Table 1. Test results

 Nominal concentration (mg/l)

 Geometric mean measured concentration (mg/l)  Mean yield after 72 hours (cells/mL)  Percentage inhibition of yield  Mean growth rate 0 -72 hours  Percentage inhibition of growth rate  
 Control  Control  1098489  -  1.5692  -
 7.5  0.77  1116978  -1.7  1.5749  -0.4
 15  1.2  1112844  -1.3  1.5737  -0.3
 30  1.7  1048378  4.6  1.5532  1.0
 60  2.4  1080444  1.6  1.5635  0.4
 120  3.6  1092800  0.5  1.5676  0.1
Validity criteria fulfilled:
yes
Conclusions:
A 72-hour EC50 value of >3.6 mg/l and NOEC of =3.6 mg/l have been determined for the effects of the test substance on yield and growth rate of Pseudokirchnerella subcapitata based on geometric mean measured exposure concentrations of the test substance. The test substance is known to hydrolyse rapidly in water and 3.6 mg/l was the concentration measured in the highest nominal test concentration of 120 mg/l. It is therefore likely that the test organisms were predominantly exposed to the hydrolysis products of the substance.

Description of key information

Short-term toxicity to algae: 72 hour EC50 >500 mg/l and NOEC =500 mg/l (arithmetic mean measured, highest concentration tested) (EU Method C.3 (Algal Inhibition Test triethoxy(methyl)silane (CAS 2031-67-6). The observations in this study are attributed to the exposure of test organisms to the hydrolysis products in the test system. The EC50 and NOEC are equivalent to >213.7 mg/l and =213.7 respectively, when expressed in terms of the silanol hydrolysis product.

Key value for chemical safety assessment

Additional information

There are no reliable short-term invertebrate toxicity data available for methylsilanetriyl triacetate (CAS 4253-34-3), therefore good quality data for appropriate structural analogues triethoxy(methyl)silane (CAS 2031-67-6) and trimethoxy(methyl)silane (CAS 1185-55-3), have been read across. The substances share the same silanol hydrolysis product, methylsilanetriol. The other hydrolysis products are acetic acid, ethanol and methanol, respectively. In the tests with triethoxy(methyl)silane (CAS 2031-67-7) and trimethoxy(methyl)silane (CAS 1185-55-3), the observations are attributed to the exposure of test organisms to methylsilanetriol in the test system. There is no basis to expect that ethanol or methanol significantly influenced the results of the tests. The toxicity of ethanol and methanol is discussed further in the ecotoxicological information overview endpoint summary (additional information).

 

A 72 hour EC50 value of >500 mg/l and NOEC of =500 mg/l (arithmetic mean measured, highest concentration tested) have been determined for the effects of triethoxy(methyl)silane (CAS 2031-67-6) on growth rate of Pseudokirchneriella subcapitata. 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 concentration of the hydrolysis product, methylsilanetriol, by applying a molecular weight correction to the nominal test substance concentration: (MW of silanol = 94.14 / MW of parent = 220.26) * EC50 >500 mg/l and NOEC =500 mg/l = EC50 >213.7 mg/l and NOEC =213.7 mg/l. These values are read across to methylsilanetriol without further correction.

A 72 hour EC50 value of >120 mg/l and NOEC of =120 mg/l (nominal, highest concentration tested) have been determined for the effects of trimethoxy(methyl)silane (CAS 1185-55-3) on growth rate of Pseudokirchneriella subcapitata. The test substance is known to hydrolyse rapidly in water and the measured concentration of parent substance was 3.6 mg/l at the end of the test. It is therefore likely that the test organisms were predominantly exposed to the hydrolysis products of the substance.