Tetraethyl orthosilicate

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2006-09-06 to 2006-09-08

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Prior to the start of the definitive exposure, one water sample was removed from the high, middle and low treatment levels and the control solution and analyzed for ethyl silicate concentration. Results of these pretest analyses were used to judge whether sufficient quantities of ethyl silicate were being delivered to the test vessels and whether the appropriate test concentrations were being maintained in order to initiate the definitive exposure.

During the in-life phase of the definitive study, one water sample (alternating between replicates A and B) from each treatment level and the control solution was collected, extracted and analyzed for ethyl silicate at 0 hour (test initiation) and 48 hours (test termination). Samples were collected from the approximate midpoint of the test vessel by pipet.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: During the definitive study, ethyl silicate (density 0.93 g/mL, 930 mg a.i./mL) was delivered directly into the diluter's mixing chamber via syringe. The resulting solution was observed to be clear and colourless with an oily film of undissolved substance on the solution's surface. A Glenco® 50 -mL gas-tight syringe in conjunction with a Harvard Syringe Pump was calibrated to deliver 0.2118 mL/cycle of the 930 mg a.i./mL ethyl silicate solution into the diluter system's chemical mixing chamber which also received 0.390 L of dilution water per cycle. The mixing chamber was positioned over a water-driven magnetic stirrer and was partially submerged within an ultrasonic water bath which continuously mixed the contents of the mixing chamber. The concentration of ethyl silicate in the solution contained within the mixing chamber was equivalent to that of the highest nominal test concentration (500 mg a.i./L) and was proportionally diluted (50%) to produce the remaining nominal test concentrations (250, 125, 63, 3l and 0 (control) mg a.i./L).

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source: From laboratory stock cultures

- Age at study initiation (mean and range, SD): <24 hours

- Method of breeding: Juvenile daphnids (< 24 hours old) were obtained from the laboratory cultures by removing all immature daphnids from the culture vessels 24 hours prior to test initiation, thereby isolating all mature gravid adult daphnids in the culture. Daphnids produced by these adult organisms were removed from the cultures and used as test organisms. The adult daphnids used to produce offspring for this test (l) did not contain ephippia, (2) produced offspring prior to being l2 days old, (3) were not used in any portion of a previous test and (4) mortality 48 hours prior to test initiation was < 20%.

CULTURE CONDITIONS

- Culture medium: The culture water was prepared by fortifying well water based on the formula for hard water and filtering it through an Amberlite XAD-7 resin column to remove any potential organic contaminants. This water had a total hardness range and total alkalinity as calcium carbonate (CaCO3) of 160 to 170 mg/L and 110 mg/L, respectively, a pH range o f 7.9 to 8.2, a dissolved oxygen concenration range of 7.5 to 9.7 mg/L, a temperature range of 20 to 22ºC and a specific conductance range of 500 to 600 micromhos per centimetre. All water quality ranges presented here were measured during the two weeks prior to testing.

- Lighting: The daphnid culture area received a regulated photoperiod of 16 hours of light and 8 hours of darkness. Light intensity of 68 to 99 footcandles (730 to 1100 lux) at the surface of the culture solutions was provided by fluorescent bulbs.

- Feeding of stock cultures: Daphnids were fed a unicellular green algae (Ankistrodesmus falcatus, 4 x l0E7 cells/ml) at a rate of 0.5 to 1.5mL per vessel daily depending on the age of the adult organisms in the culture vessel and 0.5 mL of a combination of yeast, cereal leaves and flaked fish food (YCT) daily. Daphnids were not fed during the exposure.

- Feeding during test: None

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

160-170 mg/L as CaCO3

Test temperature:

21 to 23ºC

pH:

8.0 to 8.1

Dissolved oxygen:

7.2 to 8.8 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (control), 31, 63, 125, 250 and 500 mg a.i./L

Mean measured concentrations ranged from 15 to 37% of nominal levels and were defined as < LoQ (Control), 11, 14, 34, 70 and 75 mg a.i./L.

Analytical variability in the two highest test concentrations was likely due to solubility of the test substance under the test conditions maintained.

Details on test conditions:

TEST SYSTEM

- Exposure vessel type (e.g., size, headspace, sealed, aeration, # per treatment):  Each test vessel (1600-mL square glass battery jars) had two 2-cm holes drilled in the sides, 15 cm from the bottom, which were covered with Nitex® 40 mesh screen for drainage.  The total test solution volume was maintained at 1400 mL.  Two replicate test vessels were established for each treatment level and a dilution water control.  No aeration was provided to the test vessels. 

- Dilution water source:  Fortified well water based on the formula for hard water (U.S. EPA, 1975). Dilution water chemistry (hardness, alkalinity, pH, TOC):  The dilution water had a total hardness range and alkalinity as CaCO3 of 160 to 170 mg/L and 110 mg/L, respectively, a pH range of 8.1 to 8.2 and a specific conductivity range of 500 to 600 µmhos/cm.  The TOC concentration of the dilution water was 0.38 mg/L for the month of September 2006.  

- Lighting (quality, intensity, and periodicity):  The test area was illuminated with fluorescent bulbs.  The test area received a regulated photoperiod of 16 hours of light and 8 hours of darkness.  Sudden transitions from light to dark and vice versa were avoided.  Light intensity was measured once during the test.

- Water chemistry in test (D.O., pH), in the control, and at least one concentration where effects were observed:  The dilution water control vessels had a measured DO concentration of 8.8 mg/L at test initiation and test termination.  The pH measured in the dilution water control vessel replicates was 8.1 at test initiation and ranged from 8.0 to 8.1 at test termination.  

- Element (unit) basis (i.e., immobilization):  Immobilization

- Test design (number of replicates, individuals per replicate, concentrations):  Twenty daphnids were impartially selected and distributed to each concentration and the control (two replicates, ten daphnids per replicate vessel).  

- Method of calculating mean measured concentrations (i.e., arithmetic mean, geometric mean, etc.):  Arithmetic mean.  

Reference substance (positive control):

no

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

>= 75 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 75 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

- Immobilisation of control: 0

Reported statistics and error estimates:

There were no significant effects on mobility at any of the test concentrations and therefore statistical analysis of the results was not required.

Table 1. Results of analysis of test media

Nominal concentration (mg/L)	Measured concentration at start of test (mg/L)	Measured concentration at end of test (mg/L)	Mean measured concentration (mg/L)	Mean measured concentration as % of nominal
0 (Control)	<0.44	<0.46	Not applicable	Not applicable
31	12	10	11	37
63	14	13	14	22
125	37	30	34	27
250	79	61	70	28
500	59	91	75	15

Table 2. Test results

Mean measured concentration (mg/L)	Percentage immobilisation after 24 hours	Percentage immobilisation after 48 hours
0 (Control)	0	0
11	0	0
14	0	0
34	0	0
70	0	0
75	0	5

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 value of >75 mg/L and NOEC of ≥75 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna. Under the flow-through exposure conditions used in the test it is likely that the test organism will have been primarily exposed to the test substance.

Reference 2

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1993-10-11 to 1993-10-15

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

NOEC and EC50 are based on a single measurement of the stock solution before dilution and addition to test vessels.

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Version / remarks:

Cited as Directive 84/449/EEC, C.2 (Acute toxicity for Daphnia)

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

The measured Dissolved Organic Carbon Concentration was determined in the fresh stock solution that was used to prepare the test media..

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: The hard-to-dissolve test substance was added to the synthetic fresh water to provide a concentration of 1 g/l, and was stirred for 18 hours.  Then the solution was filtered and the carbon content was determined.  This solution served as the initial solution and contained a DOC value of 433 mg/l, which corresponds to a substance content of 938 mg/l.  Test concentrations selected for the main test were 235, 328, 469, 657, and 844 mg/l. 

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source: Daphnia magna were produced through internal self-production.  The mother specimens were maintained in M4 medium per Elendt in 1-liter beakers for breeding.  The daily amount of nutrient, consisting of Scenedesmus subspicatus, was so measured that the amount added was totally consumed by the specimens.  At regular intervals of about four weeks, the young were isolated from the tanks.  They were the basis for further breeding.  Juveniles (less than 24 hours old) were isolated and used for testing in synthetic fresh water (294 mg/l CaCl2 x 2 H2O; 123 mg/l MgSO4 x 7 H2O; 63 mg/l NaHCO3; 5.5 mg/l KCl; the sum of the Ca2+ and Mg2+ was 4:1, and the ratio of Na+ to K+ was 10:1).

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

-

Test temperature:

20+/-1ºC

pH:

7.0-7.1

Dissolved oxygen:

7.8-8.5 at test termination

Salinity:

Not applicable

Nominal and measured concentrations:

Test concentrations selected for the main test were 0(Control), 235, 328, 469, 657, and 844 mg/l based on the measured concentration in the stock solution. 

Details on test conditions:

Static exposure tests were conducted at 20 + 1oC.  The tests were conducted in the dark.  The test vessels were glass cylinders graduated to 10 ml.  Four vessels, each containing five neonates, were used for each test concentration and for the control (total of 20 neonates/test concentration).  The test organisms were not fed during the test and no aeration was applied.  Test organisms were observed for mortality (immobilization) at 24 and 48 hours after test initiation.  Dissolved oxygen and pH were measured at test termination for each test concentration and control. 

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

>= 844 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 844 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

48 h

Dose descriptor:

LOEC

Effect conc.:

> 844 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

- Immobilisation of control: 0

Results with reference substance (positive control):

The previous test conducted with the positive control, potassium dichromate, showed 20% immobilization at 24-hours with 0.9 mg/l, and 100% immobilization at 24-hours with 1.9 mg/l.

Reported statistics and error estimates:

There were no significant effects in the test and therefore statistical analysis of the results was not required

There was no immobilisation at any test concentration or in the control group.  

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 value of >844 mg/L and a NOEC of ≥844 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Description of key information

Short-term toxicity to invertebrates:

WoE: 48-hour EC₅₀ >844 mg/l (based on DOC analysis of initial stock solution) (highest concentration tested) (test guideline EU method C.2 (Acute Toxicity for Daphnia)). The EC₅₀ is equivalent to >389 mg/l when expressed in terms of the silanol hydrolysis product.

WoE: 48-hour EC₅₀ >75 mg/l (measured concentration, based on analysis of the parent substance by GC/FID) (highest measured concentration tested) (test guideline OECD TG 202 (Daphnia sp. Acute immobilisation test)).

Additional information

A 48-hour EC₅₀ value of >844 mg/l (based on DOC analysis of initial stock solution) (highest concentration tested) has been determined for the effects of tetraethyl orthosilicate (CAS 78-10-4; EC No. 201-083-8) on mobility of Daphnia magna (Hüls, 1989) in accordance with test guideline EU method C.2 (Acute Toxicity for Daphnia) and in compliance with GLP. In view of the test media preparation method/exposure regime (stirring for 18 hours/static 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, monosilicic acid, by applying a molecular weight correction: (MW of silanol = 96.1 / MW of parent = 208.33) * >844 = >389 mg/l.

A second toxicity to invertebrates test was carried out with tetraethyl orthosilicate (CAS 78-10-4). A 48-hour EC₅₀ value of >75 mg/l (measured concentration, based on analysis of the parent substance by GC/FID) (highest measured concentration tested) has been determined for the effects of the substance on mobility of Daphnia magna (Springborn Smithers, 2006) in accordance with OECD TG 202 (Daphnia sp. Acute immobilisation test) and in compliance with GLP. The highest nominal concentration tested was 500 mg/l, which was equivalent to a mean measured concentration of 75 mg/l. The low analytical recovery compared to the nominal concentration was due to removal of test substance by hydrolysis. Despite the flow-through regime of the test, the test organisms were therefore exposed to a mixture of the parent substance and its hydrolysis products.

Both tests are used as weight of evidence to demonstrate that no acute toxicity is caused by exposure of the test organisms to tetraethyl orthosilicate (CAS 78-10-4) and its hydrolysis products.

Refer to IUCLID Section 6, CSR Section 7.0, for further discussion of the approach to chemical safety assessment.