Silicon dioxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

15 May 2019 to 22 May 2019 (experimental phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))

Version / remarks:

2010

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Version / remarks:

2015

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: The test item was pipetted directly into the test vessels;
- Controls: yes, maintained under identical conditions but not exposed to test item.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Pretreatment: Upon arrival in the test facility, the sludge was filtrated, washed with tap water 3 times and re-suspended in tap water. The activated sludge was aerated until usage in the test and fed daily with 50 mL synthetic sewage feed /L
- The dry matter was determined as 3.1 g suspended solids/L, giving a concentration of 1.55 g suspended solids/L in the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Post exposure observation period:

no

Hardness:

0.88 mM

Test temperature:

18.5 – 20.9 °C

pH:

8.2-8.3 (controls 8.3)

Salinity:

not appplicable

Conductivity:

210 µS/cm

Nominal and measured concentrations:

2.5, 25, 250 and 2500 mg/L (nominal, corresponding to 1, 10, 100 and 1000 mg/L SiO2 in the test item)

Details on test conditions:

TEST SYSTEM
- Test vessel: Glass beakers (800 – 1000 mL) were used as test vessels.Narrow-neck glass bottles with flat bottoms (250 mL) were used for O2 measurements.
- Aeration: purified air, using Pasteur pipettes;
- No. of vessels per concentration (replicates): 1 (lower concentrations), 5 (highest concentration)
- No. of vessels per control (replicates): 1 (positive control), 2 before and 2 after measuring positive control and test item, respectively.
- No. of vessels per abiotic control (replicates): -
TEST WATER PARAMETERS
- Source/preparation of dilution water: Laboratory tap water, CoA available;
SYNTHETIC SEWAGE
- as per guideline;
EFFECT PARAMETERS MEASURED: oxygen consumption after 3 hours;

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 2 500 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks on result:

other: value corresponds to >1000 mg SiO2/L

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

2 500 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks on result:

other: value corresponds to 1000 mg SiO2/L

Details on results:

Validity criteria were fulfilled:
- The coefficient of variation of oxygen uptake rate in control replicates was +/- 6.9% (i.e. less than 30%)
- The mean specific respiration rate of the blank controls was 27.61 mg oxygen per gram dry weight of sludge per hour (i.e. was > 20 mg oxygen per gram dry weight of sludge per hour).
- The reference substance results were valid, the EC50 for 3,5-dichlorophenol was within the expected range: 2 to 25 mg/L.

Results with reference substance (positive control):

Results with reference substance valid: yes
- 3,5-dichlorophenol, EC50 (3 hours): 10 mg/L (95% CI 5.4-15 mg/L);

Reported statistics and error estimates:

For the treatments with the test item concentration 2500 mg/L (corresponding to 1000 mg SiO2/L), it was tested whether the differences between treatment and blank control were significant. Based on equality of variance, the t-test was used (level of significance: 95%).

Validity criteria fulfilled:

yes

Conclusions:

The effect of the test item on the respiration of activated sewage sludge resulted in a 3 -hour EC50 of > 2500 mg/L (corresponding to 1000 mg SiO2/L). The No Observed Effect Concentration (NOEC) after 3 hours exposure was 2500 mg/L (corresponding to 1000 mg SiO2/L)

Executive summary:

A GLP study was performed to assess the effect of the test item on the respiration of activated sewage sludge. The method followed that described in the OECD Guidelines for Testing of Chemicals No 209, adopted in 2010 and Commission Regulation (EU) No. 2016/266 amending Regulation (EC) No. 440/2008, EU-Method C.11., adopted in 2015. Activated sewage sludge from a mainly domestic sewage treatment plant was exposed to the test item at concentrations of 2.5, 25, 250, and 2500 mg/L (corresponding to 1, 10, 100 and 1000 mg SiO2/L) at a temperature of 20 +/- 2 °C for a period of 3 hours with the addition of synthetic sewage as respiratory substrate. The rate of respiration was determined after 3 hours contact time and compared to data for the control and a reference material, 3,5-dichlorophenol. The effect of the test item on the respiration of activated sewage sludge resulted in a 3 -hour EC50 of > 2500 mg/L. The No Observed Effect Concentration (NOEC) after 3 hours exposure was 2500 mg/L (corresponding to 1000 mg SiO2/L).

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 January 2020 to 15 January 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

July 22, 2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Customer grade: S-17D

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Pretreatment:
Upon arrival in the test facility, the sludge was washed with reconstituted water and centrifuged. The supernatnt was decanted after centrifugation of the sludge and this washing procedures was performed at least twice. The activated sludge was aerated until usage in the test and fed daily with 50 mL synthetic sewage feed /L.
- The dry matter was determined as 3.75 g suspended solids/L (± 10%), giving a concentration of 1.5 g suspended solids/L (± 10%) in the test.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18.2–19.8 °C

pH:

7.4 (definitive test); 7.4-7.5 (reference test)

Nominal and measured concentrations:

Limit test: 1000 mg/L (nominal)

Details on test conditions:

The test solutions were stirred at test temperature for 24±1 hours before start of exposure to yield a suspension.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol (3,5-DCP)

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: after stirring, the test solution appeared as a homogeneous, slightly turbid suspension.
- Effect concentrations exceeding solubility of substance in test medium: solubility was exceeded;
- Adsorption (e.g. of test material to the walls of the test container): none reported
- Blank controls oxygen uptake rate: 60.8 and 48.8 mg O2/L.h
- Coefficient of variation of oxygen uptake rate in 3 control replicates: 14.9 and 3.8

 

Results with reference substance (positive control):

Results with the reference substance were valid. The EC50 for 3,5-dichlorophenol was determined to be 7.10 mg/L (acceptable range: 2- 5 mg/L)

Reported statistics and error estimates:

The EC50 of the reference substance was calculated with probit analysis (i.e. cumulative distribution function (CDF) using a non-linear regression without weighting) using the softwareToxRat Professional 3.3.0.

Validity criteria fulfilled:

yes

Conclusions:

The definitive (limit) test showed no inhibition of total respiration rate of the inoculum at 1000 mg test item/L compared to the control respiration. The EC50 is therefore expressed as > 1000 mg test item/L.

Executive summary:

The study was conducted according to OECD test guideline 209 (2010) as a limit test. The test substance did not show no inhibition of total respiration ratea at 1000 mg/L. The 3 hour EC50 of the test substance was calculated as >1000 mg/L. Thus the NOEC was determined to be 1000 mg/L.

Reference 3

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 January 2020 to 15 January 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

July 22, 2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Pretreatment:
Upon arrival in the test facility, the sludge was washed with reconstituted water and centrifuged. The supernatnt was decanted after centrifugation of the sludge and this washing procedures was performed at least twice. The activated sludge was aerated until usage in the test and fed daily with 50 mL synthetic sewage feed /L.
- The dry matter was determined as 3.75 g suspended solids/L (± 10%), giving a concentration of 1.5 g suspended solids/L (± 10%) in the test.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18.2–19.8 °C

pH:

7.4 (definitive test); 7.4-7.5 (reference test)

Salinity:

not appplicable

Nominal and measured concentrations:

Limit test: 1000 mg/L (nominal)

Details on test conditions:

The test solutions were stirred at test temperature for 24±1 hours before start of exposure to yield a suspension.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol (3,5-DCP)

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: after stirring, the test solution appeared as a homogeneous, slightly turbid suspension.
- Effect concentrations exceeding solubility of substance in test medium: solubility was exceeded;
- Adsorption (e.g. of test material to the walls of the test container): none reported
- Blank controls oxygen uptake rate: 60.8 and 48.8 mg O2/L.h
- Coefficient of variation of oxygen uptake rate in 3 control replicates: 14.9 and 3.8
 

Results with reference substance (positive control):

Results with the reference substance were valid. The EC50 for 3,5-dichlorophenol was determined to be 7.10 mg/L (acceptable range: 2- 5 mg/L)

Reported statistics and error estimates:

The EC50 of the reference substance was calculated with probit analysis (i.e. cumulative distribution function (CDF) using a non-linear regression without weighting) using the softwareToxRat
Professional 3.3.0.

Validity criteria fulfilled:

yes

Conclusions:

The definitive (limit) test showed no inhibition of total respiration rate of the inoculum at 1000 mg test item/L compared to the control respiration. The EC50 is therefore expressed as > 1000 mg test item/L.

Executive summary:

The study was conducted according to OECD test guideline 209 (2010) as a limit test. The test substance did not show no inhibition of total respiration ratea at 1000 mg/L. The 3 hour EC50 of the test substance was calculated as >1000 mg/L. Thus the NOEC was determined to be 1000 mg/L.

Reference 4

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 January 2020 to 15 January 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

July 22, 2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Pretreatment:
Upon arrival in the test facility, the sludge was washed with reconstituted water and centrifuged. The supernatnt was decanted after centrifugation of the sludge and this washing procedures was performed at least twice. The activated sludge was aerated until usage in the test and fed daily with 50 mL synthetic sewage feed /L.
- The dry matter was determined as 3.75 g suspended solids/L (± 10%), giving a concentration of 1.5 g suspended solids/L (± 10%) in the test.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18.2–19.8 °C

pH:

7.4 (definitive test); 7.4-7.5 (reference test)

Salinity:

not appplicable

Nominal and measured concentrations:

Limit test: 1000 mg/L (nominal)

Details on test conditions:

The test solutions were stirred at test temperature for 24±1 hours before start of exposure to yield a suspension.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol (3,5-DCP)

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: after stirring, the test solution appeared as a homogeneous, slightly turbid suspension.
- Effect concentrations exceeding solubility of substance in test medium: solubility was exceeded;
- Adsorption (e.g. of test material to the walls of the test container): none reported
- Blank controls oxygen uptake rate: 60.8 and 48.8 mg O2/L.h
- Coefficient of variation of oxygen uptake rate in 3 control replicates: 14.9 and 3.8

 

Results with reference substance (positive control):

Results with the reference substance were valid. The EC50 for 3,5-dichlorophenol was determined to be 7.10 mg/L (acceptable range: 2- 5 mg/L)

Reported statistics and error estimates:

The EC50 of the reference substance was calculated with probit analysis (i.e. cumulative distribution function (CDF) using a non-linear regression without weighting) using the softwareToxRat Professional 3.3.0.

Validity criteria fulfilled:

yes

Conclusions:

The definitive (limit) test showed no inhibition of total respiration rate of the inoculum at 1000 mg test item/L compared to the control respiration. The EC50 is therefore expressed as > 1000 mg test item/L.

Executive summary:

The study was conducted according to OECD test guideline 209 (2010) as a limit test. The test substance did not show no inhibition of total respiration ratea at 1000 mg/L. The 3 hour EC50 of the test substance was calculated as >1000 mg/L. Thus the NOEC was determined to be 1000 mg/L.

Description of key information

For the assessment of the aquatic toxicity of synthetic amorphous silica (SAS) to microgranisms, the database compiles 4 studies from 2019 and 2020. All these studies were conducted according to OECD TG 209 and EC guidelines under GLP. In conclusion none of the examined test items did show a relevant respiratory inhibition to microorganisms up to and including the highest tested concentration of 1000 mg/L (tested as suspensions).

Additional information

EC50 value was not determined in all studies within the range of test concentrations up to and including the concentration limit of 1000 mg/L recommended in the current OECD TG 209.