Trimethoxysilane

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:

2004-05-06 to 2004-05-09

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Guideline study with GLP but no analysis of exposure concentrations

Qualifier:

according to guideline

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):

Raphidocelis subcapitata (previous names: Pseudokirchneriella 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 millilitres of the appropriate exposure solution was placed in each replicate flask. A 0.226mL inoculum of Pseudokirchneriella subcapitata cells, at a density of approximately 443 x 10(4) cells/mL, was aseptically introduced into each flask. This inoculum, once diluted with test media, 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

Key result

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:

other: growth rate and biomass

Key result

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:

other: growth rate and biomass

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 treatment level in accordance with OECD guidance. No test concentration resulted in >50% effect on growth and therefore the EC50 values were estimated empirically from the data as being >than the highest treatment.

After 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 mg a.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 Pseudokirchneriella subcapitata. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Description of key information

72-hour ErC₅₀: >100 mg/L and NOEC: <6.3 mg/L, growth rate of Pseudokirchneriella subcapitata.

Additional information

A 72-hour ErC₅₀ value of >100 mg/L and NOEC value of <6.3 mg/L (nominal concentration) have been determined for the effects of trimethoxysilane (CAS 2487-90-3) on growth rate of the freshwater algae Pseudokirchneriella subcapitata, in accordance with OECD 201 and in compliance with GLP. (Springborn Smithers, 2004c).

 

The test substance is susceptible to hydrolysis and due to the test media preparation (stirring overnight) and exposure regime (static), it is likely that the test organisms were predominantly exposed to the hydrolysis products of the substance, monosilicic acid and methanol.