Silicon dioxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

10 February 2017 to 08 March 2017 (in-life phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

yes

Remarks:

Temperature was not always in the recommended range. Because no immobility was observed in blank controls, this was considered not to have an impact on the validity of the study results

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

The content of silicon in the solutions was measured at the beginning in the freshly prepared solutions and at the end of the test after 21 days in the old solutions. Additionally, the content of silicon in the solutions was measured at each medium renewal in the fresh and the old solutions.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A saturated solution was prepared for the test using plastic vessels. A stock solution of 50g/L in dilution water was prepared. After homogenisation by using an ultrasonic bath for 1 min and shaking vigorously for 72 ± 2 hours, undissolved test item, was removed by centrifugation at 4500 rpm for 10 minutes followed by filtration using several 0.45 µm nylon filters. The clear liquid was used for the OECD 211 test. The lower treatments were prepared by diluting of this saturated solution with dilution water.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water flea
- Strain/clone: Daphnia magna STRAUS, Berlin
- Age at study initiation: between 0 and 24 hours. The animals which were used in the test did not belong to the first brood of the respective parent animals.
- Source: in-house
- Food type: green alga (Desmodesmus subspicatus)

22 hours before the start of the test, the adult animals were separated from the young. 0.5 hours before test start, the adults were caught with the help of a glass tube, and the newborn daphnia (age < 24h) were sieved from the medium and immediately placed into a beaker containing dilution water. After a settling-in period, animals which showed no apparent damage were used for the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Post exposure observation period:

no

Hardness:

Blank controls: 356, old: 356
Test solution: -267-346, old: 356

Test temperature:

18.2 – 22.6 °C

pH:

pH range: 6.2 – 8.4
pH variation: +/-2.2

Dissolved oxygen:

> 8.1 mg/L

Salinity:

not applicable

Conductivity:

not reported

Nominal and measured concentrations:

50 g/L loading dose (nominal), WAF diluted to correspond to 23, 10, 4.7, 2.1 g/L nominal concentrations

Details on test conditions:

Loading 80 mL/animal, animals were kept individually
Replicates 10 replicates/treatment
Blank Control dilution water
Lighting 1000 Lux
Aeration none
Feeding 0.15 - 0.20 mg org. carbon/animal/day, the amount of carbon is based on photometric measurement (linear correlation between absorption at 440 nm and measured DOC concentration).

Reference substance (positive control):

no

Key result

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

149.2 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat. (dissolved fraction)

Remarks:

filtrated (0.45 um nylon filter) WAF (72 h, room temperature)

Basis for effect:

mortality

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

68 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat. (dissolved fraction)

Remarks:

filtrated (0.45 um nylon filter) WAF (72 h, room temperature)

Basis for effect:

mortality

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

149.2 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat. (dissolved fraction)

Remarks:

filtrated (0.45 um nylon filter) WAF (72 h, room temperature)

Basis for effect:

reproduction

Details on results:

The offspring of the animals was counted three times a week. Significant decrease in the reproduction of the daphnia could not be observed in any treatment but the highest test concentration showed significant mortality of 50 %. The lower concentrated treatment and the control showed no mortality.

Results with reference substance (positive control):

not used

Reported statistics and error estimates:

The estimation of the biological results for inhibition of reproduction was accomplished using the software ToxRat® Professional, version 3.2.1

Validity

Parameter	Valid, if	Found Value
Mortality of parent animals in the control	≤ 20 %	0
Mean surviving offspring in the control	≥60	73

 

 

Validity criteria fulfilled:

yes

Conclusions:

No effects on daphnid reproduction were found at the limit of solubility. The NOEC for mortality was at 68 mg/L (dissolved fraction).

Executive summary:

A GLP study in daphnia according to OECD testing guideline was performed using 5 concentrations ranging from nominal 50 to 2.1 g/L. 10 daphnia each were exposed to the test item and the blank control for 21 days. The measured concentrations in the highest concentrated treatment can be stated as limit of solubility (149.2 mg/L). Therefore, the determination of the results was based on the geometric mean of the measured concentrations. No effects on daphnid reproduction were found at the limit of solubility. The NOEC for mortality was at 68 mg/L (dissolved fraction).

Reference 2

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

31 March 2019 to 24 April 2019 (in-life phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

yes

Remarks:

Temperature was not always in the recommended range. This was considered not to have an impact on the validity of the study results

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

The content of silicon as component of the test item in the test solutions was measured at the beginning in the freshly prepared solutions and at the end of the test in the used solutions. Additionally, the content of silicon was measured in the same batch of the test solution (fresh and old) once a week.
In the control solution the content of silicon was measured only at the beginning and at the end of the test. On day 14 Tyndall effect was measured in one batch of the freshly prepared and the used test solutions.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
M-4 medium was added to 50 ± 1 g test item to reach a nominal load of 50 g/L. After homogenisation by using an ultrasonic bath for 1 min and shaking vigorously for 72 hours, undissolved test item was removed by centrifugation at 4500 rpm for 10 minutes followed by filtration using nylon filters (0.45 µm). The clear liquid was used for the OECD 211 test. The lower treatment (5 g/L) was prepared by diluting the saturated solution with M4-medium.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water flea
- Strain/clone: Daphnia magna STRAUS, Berlin
- Age at study initiation: between 0 and 24 hours. The animals which were used in the test did not belong to the first brood of the respective parent animals.
- Source: in-house
- Food type: green alga (Desmodesmus subspicatus)
22 hours before the start of the test, the adult animals were separated from the young. 0.5 hours before test start, the adults were caught with the help of a glass tube, and the new-born daphnia (age < 24h) were sieved from the medium and immediately placed into a beaker containing dilution water. After a settling-in period, animals which showed no apparent damage were used for the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Post exposure observation period:

no

Hardness:

Hardness was measured in fresh and old test solutions (control and highest test concentration) once per week; no difference between blank controls and test solutions was noted.

Test temperature:

19.5 to 24.0 °C

pH:

pH range blank control: old 7.6 – 8.7, new 8.4-8.8
pH range test solution: old 7.6 – 8.1, new 7.2-8.0
pH variation: 0.8 (valid if less or equal to 1.5)

Dissolved oxygen:

O2 in mg/L:
blank: old 7.9-9.7, fresh 8.8-9.6
test solution: old 8.0-9.2, fresh 8.5-9.3

Salinity:

not applicable

Conductivity:

not reported

Nominal and measured concentrations:

Dissolved fraction (72h in M4-medium) after 50 g/L loading, and 1:10 dilution thereof

Details on test conditions:

TEST SYSTEM
- Test vessel: 100 mL glass beakers
- Renewal rate of test solution: 3 times/week
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Elendt M-4 medium, also used for dilution

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 16/8 hours, using neon tubes; 1000 Lux

EFFECT PARAMETERS MEASURED:
- number of offspring (after 21d and at each medium renewal)
- total offspring per surviving parent

TEST CONCENTRATIONS
- Range finding study: no
- Test concentrations: 50 g/L loading rate

Reference substance (positive control):

no

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

132.7 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat. (dissolved fraction)

Remarks:

filtrated (0.45 um nylon filter) WAF (72 h, room temperature)

Basis for effect:

reproduction

Details on results:

In addition to standard parameters, calcium and magnesium concentrations were determined in freshly prepared test solutions, after shaking for 72 hours, and during the test in fresh and old test solutions. A decrease of calcium and magnesium was measured, which is most likely due to an interaction of silica with components of the M4 medium. Losses of Ca and Mg due to the presence of the test organisms and algae were excluded.

Results with reference substance (positive control):

not used

Reported statistics and error estimates:

No decrease in the reproduction of the daphnia could be observed in any treatment. The number of offspring in the test solutions was slightly higher than in the control. Therefore, no statistical evaluation was performed.

Treatment Loading Rate	Total Offspring	Surviving Parent Animals	Mean Offspring per Surviving Parent Animal	Inhibition of Reproduction in %
Blank Control	688	9	76	0
5 g/L	836	9	93	-22
50 g/L	777	9	86	-13

 

 

Table: pH, O₂, Hardness (mg CaCO3/L)

	pH		O2-Value		Hardness
	old	new	old	new	old	new
Blank Control	7.6 – 8.7	8.4 – 8.8	7.9 – 9.7	8.8 – 9.6	267	267
Test Item	7.6 – 8.1	7.2 – 8.0	8.0 – 9.2	8.5 – 9.3	267	267

 

Validity

Parameter	Validity criterium	Found Value
Mortality of parent animals in the control	≤ 20 %	10 %
Mean surviving offspring in the control	≥60	76

 

Validity criteria fulfilled:

yes

Conclusions:

No adverse effects on daphnid reproduction were found at 132 mg/L (dissolved fraction, nominal loading 50g/L, 72h stirring in M4-medium).

Executive summary:

A GLP reproductive toxicity study in daphnia according to OECD and EC testing guidelines was performed using the dissolved fraction (filtrate after 72h stirring in M4 medium) of a 50 g/L loading and the 1:10 dilution thereof. 10 daphnia each were exposed to the test solution and the blank control for 21 days. The study was performed under semi-static conditions with medium renewal three times/week. Offspring were counted at each medium renewal. The number of offspring in the test solutions was slightly higher than in the control. Therefore, no statistical evaluation was performed. In accordance with OECD GD 23, the determination of the results was based on the geometric mean of the measured concentrations. The NOEC for reproduction was at 132.7 mg/L (dissolved fraction).

Reference 3

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

06 March 2019 to 27 March 2019 (in-life phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

yes

Remarks:

Temperature was not always in the recommended range. This was considered not to have an impact on the validity of the study results

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Silicon was measured in the fresh test solutions at the beginning, after 5, 12 and 19 days and after 7, 14 and 21 days in the old solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
Stock solutions containing 250 mg/L (195 µL/L based on a density of 1.28 g/cm3) test item corresponding to 100 mg/L Synthetic Amorphous Silica) in test medium (M4-medium) were prepared. The lower treatment was prepared by dilution of these stock solutions with test medium.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water flea
- Strain/clone: Daphnia magna STRAUS, Berlin
- Age at study initiation: between 0 and 24 hours. The animals which were used in the test did not belong to the first brood of the respective parent animals.
- Source: in-house
- Food type: green alga (Desmodesmus subspicatus)
22 hours before the start of the test, the adult animals were separated from the young. 0.5 hours before test start, the adults were caught with the help of a glass tube, and the new-born daphnia (age < 24h) were sieved from the medium and immediately placed into a beaker containing dilution water. After a settling-in period, animals which showed no apparent damage were used for the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Post exposure observation period:

no

Hardness:

Hardness was measured in fresh and old test solutions (control and highest test concentration) once per week; no difference between blank controls and test solutions was noted. In both treatments hardness increased in old solutions as compared to the freshly prepared solutions.

Test temperature:

19.7 to 22.4 °C

pH:

no effect of treatment as compared to controls

Dissolved oxygen:

no effect of treatment as compared to controls

Salinity:

not applicable

Conductivity:

not reported

Details on test conditions:

TEST SYSTEM
- Test vessel: 100 mL glass beakers
- Renewal rate of test solution: 3 times/week
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Elendt M-4 medium, also used for dilution

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 16/8 hours, using neon tubes; 1000 Lux

EFFECT PARAMETERS MEASURED:
- number of offspring (after 21d and at each medium renewal)
- total offspring per surviving parent

TEST CONCENTRATIONS
- Range finding study: no
- Test concentrations: 25 and 250 mg/L, corresponding to 10 and 100 mg colloidal SAS/L

Reference substance (positive control):

no

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

250 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Remarks:

corresponding to 100 mg colloidal SAS/L

Basis for effect:

reproduction

Details on results:

Due to the loss of test item in the test solution over time (measured as decrease in silicon), most likely caused by the ingestion of test item by the test organisms, the measured concentrations of fresh solutions were used for evaluation. Because the geometric mean of the measured concentrations in these solutions was between 92 % and 98 % of the nominal concentration, the biological results were based on the nominal concentration.

Results with reference substance (positive control):

not used

Reported statistics and error estimates:

The estimation of the biological results was accomplished using the software ToxRat® Professional, version 3.3.0

Fecundity

Treatment	Total Offspring	Surviving Parent Animals	Mean Offspring per Surviving Parent Animal	Inhibition of Reproduction in %
Blank Control	701	8	88	0
25 mg/L	895	10	90	-2
250 mg/L*	743	9	83	6

* corresponding to 100 mg/L SAS

pH, O₂, Hardness

	pH		O2-Value		Hardness
	old	new	old	new	old	new
Blank Control	7.8 – 8.0	8.0 – 8.6	8.3 – 8.4	8.7 – 9.3	267 – 356	267
Test Item	7.8 – 8.0	8.0 – 8.6	8.3	8.7 – 9.2	267 – 356	267

Validity

Parameter	Validity criterium	Found Value
Mortality of parent animals in the control	≤ 20 %	20 %
Mean surviving offspring in the control	≥60	88

 

Validity criteria fulfilled:

yes

Conclusions:

No adverse effects on daphnid reproduction were found at 100 mg colloidal SAS/L

Executive summary:

A GLP reproductive toxicity study on daphnia according to OECD and EC testing guidelines was performed using colloidal silica. 10 daphnia individually held were exposed to the test solutions and the blank control for 21 days. The study was performed under semi-static conditions by frequent renewal with new medium three times a week. Offspring were counted at each medium renewal. The number of offspring in the test solutions was not different from that in the control. The NOEC for reproduction was at 250 mg/L, corresponding to 100 mg colloidal SAS/L.

Description of key information

No adverse effects on reproduction of daphnids were found in GLP studies performed in accordance with current OECD and EC guidelines, using synthetic amorphous silica (precipitated silica, silica gel and colloidal silica. The No observed effect concentrations (NOECs) for reproduction were at 100 mg/L or higher (dissolved fractions, or colloidal dispersion).

Additional information

The particulate test system of SAS was demonstrated by using stable dispersion of colloidal SAS as a worst case scenario. For the other SAS types, the dissolved fraction of SAS has been used in the respective testing. This data set covers the possible routes of exposure to SAS in the aquatic environment. As no adverse effects on reproduction of daphnids were observed in all the studies, adverse effects of pyrogenic SAS is accordingly not expected.