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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
2004-05-06 to 2004-05-09
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to an appropriate OECD test guideline with acceptable restrictions as there was no analysis of exposure concentrations
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 100 mg a.i./L. (mg active ingredient/L) stock solution was prepared by adding 215 uL of trimethoxysilane (0.1998 g based on a purity of 97.1% and a density of 0.957 g/mL) to 2000 mL of dilution water. The solution was mixed overnight with a magnetic stir plate and Teflon-coated stir bar. Each test concentration was prepared by adding the appropriate amount of the 100 mg a.i./L stock solution to an intermediate vessel and bringing it to a final volume of 1000 mL with dilution water.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM

- Strain: Psuedokirchneriella  subcapitata, formerly Selenastrum capricornutum, strain 1648,Class Chlorophyceae

- Source (laboratory, culture collection): The alga was obtained from the University of Texas, Austin, Texas and was maintained in stock culture at Springborn Smithers Laboratories. 

- Method of cultivation: The stock cultures were maintained within the following conditions: shaking rate of 100+/- 10 rpm, a temperature of 24 +/- 1 °C and continuous illumination at the surface of the medium with an intensity of 6300 to 9600 lux (590 to 890 foot candles). Lighting was supplied by fluorescent bulbs. Culture flasks were agitated continuously on an orbital shaker. 


ACCLIMATION

- Culturing media and conditions (same as test or not): No
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Hardness:
No data
Test temperature:
24°C
pH:
7.0 to 7.1 at start of test

8.6 to 9.3 at end of test
Dissolved oxygen:
No data
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control), 6.3, 13, 25, 50 and 100 mg/L
Details on test conditions:
TEST SYSTEM

- Test vessel: The test was conducted in sterile 250-mL Erlenmeyer flasks containing 100 mL of test solution. All test vessels were fitted with stainless steel caps which permitted gas exchange.

- Test Design: One hundred milliliters of the appropriate exposure solution was placed in each replicate flask. A 0.226mL inoculum of Psuedokirchneriella subcapitata cells, at a density of approximately 443 x 10(4) cells/mL, was aseptically introduced into each flask. This inoculum provided the required initial (0 hour) cell density of approximately 1.0 x 10(4)cells/mL. Three replicate test vessels were established for the treatment levels and the dilution water control.

- Water chemistry in test: TOC concentration of the AAP sample collected in May 2004 was 0.46 mg/L. Conductivity of the exposure and control solutions measured at test initiation and termination was maintained at 80 umhos/cm.  

GROWTH MEDIUM

- Standard medium used: yes

- Detailed composition if non-standard medium was used: The culture medium used was Algal Assay Procedure (AAP) medium prepared with sterile, deionized water. AAP medium used to prepare the exposure solutions was formulated in the same manner as the culture medium.


OTHER TEST CONDITIONS

- Light intensity and quality: 6500 to 8600 lux (600 to 800 footcandles). The photosynthetically-active radiation (PAR) of the test area measured at test initiation ranged from 98 to 128 uE/m2/s.

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

- Range finding study

- Test concentrations: 0.01, 0.1, 1. 10 and 100 mg/L

- Results used to determine the conditions for the definitive study: No significant difference in cell densities compared with the Control after 72 hours
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: test substance and hydrolysis product
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
other: test substance hydrolysis products
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 6.3 mg/L
Nominal / measured:
nominal
Conc. based on:
other: test substance hydrolysis products
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 6.3 mg/L
Nominal / measured:
nominal
Conc. based on:
other: test substance and hydroysis product
Basis for effect:
growth rate
Details on results:
After 72 hours of exposure, cells exposed to all the treatment levels tested and the control were observed to be normal.  The 72 hour cell density in the control averaged 154.00 x 10 (4) cells/mL. Cell densities in the 6.3, 13, 25, 50 and 100 mg a.i./L treatment levels averaged 104.75, 117.58, 104.33, 117.72 and 119.14 x 10(4) cells/mL, respectively.
Reported statistics and error estimates:
Average-specific growth rates and Areas under the growth curves were determined for each tratment level in accordance with OECD guidance. No test concentration resulted in >50% effect on growth and therefore the EC50 values were estmated empiracally from the data as being >than the highest treatment.

Aftre checking for homogeneity of variance with Bartlett's test and Shapiro-Wilks' test, the NOECs were determined by Williams' test at p≤5%.
Biomass:  The total biomass in the control averaged 101.37 x 10(4) cells-days/mL. Total biomass in the 6.3, 13, 25, 50 and 100 mg a.i./L treatment levels averaged 67.53, 73.38, 67.92, 75.81 and 70.15 x 10(4) cells-days/mL, respectively.  Williams' Test determined a significant difference in the control (101.37 x 10(4) cells-days/mL). The NOEC for total biomass was determined to be <6.3 mg a.i./L, the lowest nominal concentration tested.  Since no concentration tested resulted in >=50% inhibition, the 72-hour EbC50 was empirically estimated to be >100 mg a.i./L, the highest nominal concentration tested. Growth rate:  The 0 to 72 hour growth rate in the control averaged 1.72 days-1.  The 0-72 hour growth rate in the 6.3, 13, 25, 50 and 100 mg a.i./L treatment levels averaged 1.58, 1.63, 1.59, 1.63 and 1.63 days-1, respectively.  Statistical analysis (Williams' Test) determined a significant reduction in all treatment levels tested when compared to the growth rate in the control (1.72 days-1).  The 72 hour NOEC for growth rate was determined to be <6.3 mg a.i./L, the lowest nominal concentration tested.  Since no concentration tested resulted in >=50% inhibition, the 72-hour ErC50 was empirically estimated to be >100 mga.i./L, the highest nominal concentration tested.
Validity criteria fulfilled:
yes
Conclusions:
A 72-hour EC50 of >100 mg/L and a NOEC of <6.3 mg/L have been determined for the effects of the test substance on growth rate and biomass of Pseudokirchnerella subcapitata. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Description of key information

(72 hr) EC50 of >100 mg/L growth rate Pseudokirchnerella subcapitata.

Key value for chemical safety assessment

Additional information

No measured data are available for algae for triethoxysilane (CAS 998-30-1). However studies are available for the structurally analogous substance, trimethoxysilane (CAS 2487-90-3). It is considered appropriate to read across for algae results for trimethoxysilane (CAS 2487-90-3) to triethoxysilane (CAS 998-30-1) as both substances hydrolyse in the presence of water to yield silanetriol.Silanetriol will break down further into inorganic, naturally occurring substances such as silica and silica acid.The hydrolysis half-lives of triethoxysilane (CAS 998-30-1) and trimethoxysilane (CAS 2487-90-3) indicate that under conditions relevant to ecotoxicity assessment, both will hydrolyse to silanetriol.

A 72-hour EC50of >100 mg/l and a NOEC of <6.3 mg/l (OECD Guideline 201, Algal Growth Inhibition Test Springborne Smithers 2004) have been determined for the effects of trimethoxysilane on growth rate and biomass ofPseudokirchnerella subcapitata. It is likely that the test organisms were exposed to the hydrolysis products of the substance.