Silicon dioxide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable well documented study report which meets basic scientific principles [see time-related elimination in the following entry (Sipernat 22S)]

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Objective of study:

other: deposition and clearance of SiO2 from lung

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 413

Deviations:

yes

Remarks:

Special modifications as compared with standard study:  Focus upon lung, respiratory  tract, and regional lymph nodes. Post-exposure recovery period up to one year.

Principles of method if other than guideline:

Measurements of Si in lung and lymph nodes within repeated-dose toxicity study: Analytical method for silica determination (Report, part 1, p. 25):
Lung and lymph node tissue were ashed according to the temperature program up to 650 °C in a platinum crucible. Following this, the ash was dissolved in 10 % hydrogen fluoride for 30 min. at 50 °C, and a saturated boric acid solution (silicon standard solution, 1 mg/ml) was added. The Si content of the solution was determined using a Varian ASS flame atomic absorption spectrometer.

GLP compliance:

yes

Radiolabelling:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Central Institute for Breeding of Laboratory Animals TNO, Zeist/NL
- Age at study initiation: 4 weeks
- Weight at study initiation: 50 - 70 g
- Fasting period before study: no
- Housing: single during exposure
- Diet: no access during exposure
- Water: no access during exposure
- Acclimation period: 10 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +-2
- Humidity (%): 50 - 70
- Air changes (per hr): 12x/h
- Photoperiod (hrs dark / hrs light): no data

Route of administration:

inhalation

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel exposure chamber, multitiered (manufactered by Hazelton)
- Exposure chamber volume: 2.3 m3
- Method of holding animals in test chamber: single
- Exposure type: whole body
- Source and rate of air: Aerosol entrance at top of the chamber
- Method of conditioning air: no data
- System of generating particulates/aerosols: Institute´s dust generator with compressed air operating atomizer
- Temperature, humidity, pressure in air chamber: av. 21 - 23 °C, minimum 19.1, max. 25.4 °C /
65 - 75 % rel. humidity, during extreme weather occasionally up to 95.5 % or down to 48 %.
- Air flow rate: approx. 40 m3/h
- Air change rate: 40 / 2.3 = ~17/h
- Method of particle size determination: due to electrostatic charge of the particles not measured:
technical failure of the 10-stage Mercer cascade impactor and the QCM cascade (Report p. 16)
- Treatment of exhaust air: filtered before release


TEST ATMOSPHERE
- Brief description of analytical method used: gravimetrically - Air samples are drawn through glass fiber filters (Sartorius)
and weighed (3 - 4 time per day)
- Samples taken from breathing zone: no data

Duration and frequency of treatment / exposure:

90 day(s)

Remarks:

Doses / Concentrations:
1.3, 5.9 or 31 mg/m3 (mean analytical values)

No. of animals per sex per dose / concentration:

10 each after exposure (13 weeks) and recovery period (1, 13, 29, 39, and 52 wks):
i.e. 50 m / 50 f animals per group were kept for a recovery period of at most 52 wks 

Control animals:

yes, concurrent no treatment

Positive control reference chemical:

no, but comparative study also including quartz

Details on study design:

- Dose selection rationale: see 7.5.3

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion) of SiO2
- Tissues and body fluids sampled: lung and mediastinal lymph nodes
- Time and frequency of sampling: 1, 13, 29, 39, and 52 weeks post exposure, 10 animals each)

Statistics:

The statistical assessment of the findings for the different parameters considered was based on analysis of variance (ANOVA) and Dunnett´s test

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: rapid from lung of male rats: not determinable by means of and at selected intervals (see Table below).

Test no.:

#2

Toxicokinetic parameters:

half-life 2nd: rapid from lung of female rats: not determinable by means of and at selected intervals (see Table below).

Metabolites identified:

not measured

Absolute silicon content in lung and mediastinal lymph nodes 1 week  after exposure termination (98 days) [Report, Tab. 59 + 61]

	Lung [mg]		Lymphnodes [mg]
Aerosil 200 [mg/m3, nominal]	Male #1	Female #2	Male	Female
1	0.263 ±0.216^+) (n=3)	0.051 ±0.005 (n=3)	0.080 ±0.040^*) (n=2)	No Si detected
6	0.114 ±0.004 (n=10)	0.058 ±0.006 (n=7)	No Si detected	No Si detected
30	0.256 ±0.012 (n=10)	0.212 ±0.019 (n=10)	0.030 (n=1)	0.020 (n=1)
0	0.032 (n=1)	No Si detected	0.030 (n=1)	No Si detected

^*) One male animal showed a too high value for reasons that could not be clarified.

⁺⁾ ±SEM (Standard Error of the Mean)

^{n represents the number of animals with Si found, the total number of animals measured was always 10 per group.}

Note: No Si was detected at the other time points of 13, 29, 39, and 52 weeks post exposure.

13 weeks as the second time point post was too long as to estimate the elimination half-life.

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

excretion

Qualifier:

no guideline followed

Principles of method if other than guideline:

Study in volunteers: Oral ingestion of an SAS amount in a drink, determination of SiO2 in urine prior and after to administration.

GLP compliance:

no

Specific details on test material used for the study:

Aerosil, BET 175

Radiolabelling:

no

Species:

human

Sex:

male/female

Route of administration:

other: oral in juice

Vehicle:

other: apple juice, 0.5% suspension

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:

DIET PREPARATION
- Mixing appropriate amounts with (Type of food): 2.5 g of test substance in 0.5 L (apple juice)

VEHICLE
- Concentration in vehicle: 0.5 %
- Amount of vehicle (if gavage): 0.5 L


HOMOGENEITY:
Suspension

Duration and frequency of treatment / exposure:

1x/day, given in two portions (see below)

Dose / conc.:

5 000 other: mg/l juice

Remarks:

Doses / Concentrations:
Males: 2x 1250 mg (morning and midday) Females: 2x 1250 mg (morning and midday)

No. of animals per sex per dose / concentration:

Males: 10; Females: 2 (age 22 - 28 years)
(for each test article: 5 m+ 1 f )

Control animals:

other: untreated control = each volunteer before silica intake

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: for 3 days pre-application and for 4 days post-application, total daily urine

- Method type(s) for identification: SiO2 determination according to Baumann (after alkaline hydrolysis with molybdate)
- Limits of detection and quantification: no data

Test no.:

#1

Toxicokinetic parameters:

other: Aerosil - urinary excretion: <0.5 % of the dose applied within 4 days p.a.

Test no.:

#2

Toxicokinetic parameters:

other: FK 700 - urinary excretion: <0.5 % of the dose applied within 4 days p.a.

Daily urinary excretion of SiO₂ in volunteers before and after ingestion of synthetic amorphous silica 

Aerosil
Test person	1	2	3	10	11	12
Sum SiO2 day 1 – 3 [mg/d] (control)	34.5	86.9	62.8	40.4	25.3	36.2
Sum SiO2 day 4 – 7 [mg/d] (test phase)	32.3	64.5	61.3	60.8	44.5	52.9

FK 700
Test person	4	5	6	7	8	9
Sum SiO2 day 1 – 3 [mg/d] (control)	42.4	36.8	71.4	16.1	39.9	27.4
Sum SiO2 day 4 – 7 [mg/d] (test phase)	52.2	57.0	81.4	20.4	58.3	21.8

During the four days post-treatment, significant changes of the renal SiO2 excretion were not seen.

Daily SiO2 increments in urine after ingestion ranged between individually 7 and 23 mg, but were barely distiguishable

from the baseline level.

Aerosil:
The individual baseline values of the pretest phase were very variable and individually different, mean excretion rates ranging from 

25 to 87 mg/d. In the post-treatment phase, individual mean excretion rates ranged from 32 to 61 mg/d. 

FK 700: 
The individual baseline values of the pretest phase were very variable and individually different, mean excretion rates ranging 

from 16 to 71  mg/d. 

In the post-treatment phase, individual mean excretion rates ranged from 20 to 81 mg/d. 
   ---------------

Overall, increases in excretion of SiO2 after oral ingestion were not unequivocally detectable. 

The small apparent increases on the average of less than 0.5 % of the total dose were in marked contrast to the high dose of 2500 mg SiO2 applied.  

   --------------------------

Conclusions:

There was no unequivocal pattern: The SiO2 excretion of some probands decreased, that of others was equal to levels before intake of the compound, while others excreted more SiO2.

Executive summary:

The excretion of SiO2 was assessed in human probands. Their SiO2 excretion values were measured before (days 1-3) and after (days 4-7) intake of Aerosil on day 4.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Objective of study:

absorption

distribution

excretion

Qualifier:

no guideline available

Principles of method if other than guideline:

Si analysis: Ammonium-molybdate method according to Stegemann H and Fitzek FJ (1956): Die mikroanalytische Bestimmung von Silizium in quarz- und silikathaltigen Staubproben. Aus der deutschen Forschung der letzten Dezennien. Thieme Verlag Stuttgart 1956

GLP compliance:

no

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

female

Route of administration:

other: inhalation, subcutaneous and oral (gavage)

Vehicle:

water

Details on exposure:

no datails given

Duration and frequency of treatment / exposure:

1 months, 20 applications

Remarks:

Doses / Concentrations:
100 mg/rat = approx. 500 mg/(kg bw*d)

No. of animals per sex per dose / concentration:

20 females

Control animals:

yes, concurrent vehicle

Test no.:

#1

Toxicokinetic parameters:

C(time): Si content liver 4.2 µg (control 1.8 µg) after 20 applications (1x/d)

Test no.:

#1

Toxicokinetic parameters:

C(time): Si content spleen 5.5 µg (control 7.2 µg) after 20 applications (1x/d)

Test no.:

#1

Toxicokinetic parameters:

C(time): Si content kidney 14.2 µg (control 7.8 µg) after 20 applications (1x/d)

a) 20 hours after the last exposure 0.25 mg SiO2 were found in the lungs. After 1 and 3 months the SiO2 content was 0.105 and 0.018 mg SiO2, respectively. The excretion from lungs was approximately 93% within 3 months. In the lymph node 0.018 mg SiO2 was found after 1 month and 0.008 mg SiO2 after 3 months.
b) After 24 hours 6.89 mg SiO2 were found in the tissue at the application site. After 1 month the amount was decreased to 0.646 mg SiO2 and
after 2 months 0.298 mg SiO2 was found.
c) No clinical signs were observed. The SiO2 content in the liver was 4.2 ug (control value 1.8 ug), in the spleen 5.5 ug (7.2 ug) and in the
kidneys 14.2 ug (7.8 ug).

SUMMARY (oral)
In 20 rats receiving 20 daily oral doses of 100 mg HDK V15 per animal (about 500 mg/kg bw) each, tissue values (SiO2) apparently were very slightly increased in liver and kidney: in liver 4.2 µg (control value 1.8 µg), in the spleen 5.5 µg (7.2 µg) and in the kidneys 14.2 µg (7.8 µg).

(Note: unclear if results were normalised with reference to organ weights, i.e. per g weight or per total organ.)

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results

Executive summary:

Three studies (inhalation, subcutaneous and oral) were performed to evaluate the toxicokinetics of HDK V 15.

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2-Generation-Reproduction-Study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Reason / purpose for cross-reference:

reference to same study

Objective of study:

distribution

Qualifier:

no guideline available

Principles of method if other than guideline:

Histopathology, immunohistochemistry, EDX analysis

GLP compliance:

yes (incl. QA statement)

Remarks:

certified by Swiss Federal Office of Public Health, consumer product protection directorate, notification authority for chemicals, CH-3003 Bern, Switzerland

Specific details on test material used for the study:

NM-200 synthetic amorphous silica

Radiolabelling:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

histopathology, immunechemistry and EDX analysis of animals from TNO Triskelion study V9127 (oral two-generation reproduction study)

Route of administration:

oral: unspecified

Dose / conc.:

0 mg/kg bw/day

Remarks:

control

Dose / conc.:

1 000 mg/kg bw/day

Remarks:

liver and jejunum, colon, EDX

Dose / conc.:

100 mg/kg bw/day

Remarks:

jejunum, colon, EDX

Dose / conc.:

300 mg/kg bw/day

Remarks:

jejunum, colon, EDX

No. of animals per sex per dose / concentration:

Liver: 10 males and 10 females for 0 mg/kg bw/d (control) and 1000 mg/kg bw/d (highest dose)
Jejunum, colon: 5 females for 0 mg/kg bw/d (control), 100, 300 and 1000 mg/kg bw/d
EDX analyis: 2 females for 0 mg/kg bw/d (control) and 1000 mg/kg bw/d (highest dose)

Positive control reference chemical:

no

Details on study design:

Allocation liver: rats from P-generation (10 males and 10 females respectively, 0 mg/kg bw/d = control, 1000 mg/kg bw/d = highest dose): Liver samples were embedded in paraffin, cut at an approx. thickness of 2-4 µm and stained with hematoxylin and eosin or Sirius Red and collagen I, II and III by immunehistochemistry reaction
Allocation jejunum, colon: rats from F1-generation (5 females respectively, 0 mg/kg bw/d = control, 100, 300, 1000 mg/kg bw/d): epoxy resin embedded materials submitted from TNO: Immunohistochemistry: CD11, CD40,CD69, CD86, IL-1 beta, IL6 for immune reaction, image analysis for the lenght of jejunal villi
other available organs (liver, kidney cortex and medulla, spleen, brain great 1 and 2, brain small, urinary bladder, oesophagus, duodenum, jejunum, ileum, caecum, stomach cardia, fundus and pylorus, blood): 2 female rats from F1-generation (2 from control group, 2 from 1000 mg/kg bw/d): material submitted was embedded in epoxy resin, placed on aluminium grid, evaluated by scanning electron microscopy and energy dispersive X-ray (EDX) analysis (accelaration voltage 20kV, variable pressure), suspicious spots were evaluated at magnifications of x200 and x400

Statistics:

Image analysis on liver samples for immunehistochemistry: 3 spots with Glisson`s triade were photographed by a camera connected with Olympus CellSense System. The relative area was measured and summarized on EXCEL sheets. The results were calculated by GraphPad Prism 7. Descriptive statistics and t-test were applied.
For jejunum and colon histoimmunechemistry a semi-quantative evaluation was applied. The lenth of 5 villi (if technical possible) was measured and the results summarized on EXEL sheets. Then the results were calculated by GraphPad Prism 7. Descriptive statistics and t-test were applied.
EDX: semi-quantative analysis

Preliminary studies:

two-generation-reproduction study

Type:

distribution

Results:

No treatment related findings in liver, jejunum and colon; in terated animals tiny silicon particles found in increased incidence in the oesophagus and gastrointestinal tract.

Details on distribution in tissues:

In all animals tiny silicon particles (interpreted as Feldspar, Albit) were observed located free on the surface and hence are deemed to be dust particles. In treated animals such particles were found at increased incidence in the oesophagus and gastrointestinal tract, but not in other organs.

Key result

Transfer type:

secretion via gastric mucosa

Observation:

no transfer detectable

Metabolites identified:

not specified

Remarks:

tiny spots of Na, Al and Si, interpreted as Feldspar (Albit)

Conclusions:

Synthetic amorphous silica is not systemically distributed from the gastrointestinal tract.

Reference 5

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable well documented study report which meets basic scientific principles

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Objective of study:

other: deposition and clearance

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 413

Deviations:

yes

Remarks:

Special modifications as compared with standard study:  Focus upon lung, respiratory  tract, and regional lymph nodes. Post-exposure recovery period up to one year.

Principles of method if other than guideline:

Measurements of Si in lung and lymph nodes within repeated-dose toxicity study: Analytical method for silica determination (Report, part 1, p. 25):
Lung and lymph node tissue were ashed according to the temperature program up to 650 °C in a platinum crucible. Following this, the ash was dissolved in 10 % hydrogen fluoride for 30 min. at 50 °C, and a saturated boric acid solution (silicon standard solution, 1 mg/ml) was added. The Si content of the solution was determined using a Varian ASS flame atomic absorption spectrometer.

GLP compliance:

yes

Radiolabelling:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Central Institute for Breeding of Laboratory Animals TNO, Zeist/NL
- Age at study initiation: 4 weeks
- Weight at study initiation: 50 - 70 g
- Fasting period before study: no
- Housing: single during exposure
- Diet: no access during exposure
- Water: no access during exposure
- Acclimation period: 10 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +-2
- Humidity (%): 50 - 70
- Air changes (per hr): 12x/h
- Photoperiod (hrs dark / hrs light): no data

Route of administration:

inhalation

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel exposure chamber, multitiered (manufactered by Hazelton)
- Exposure chamber volume: 2.3 m3
- Method of holding animals in test chamber: single
- Exposure type: whole body
- Source and rate of air: Aerosol entrance at top of the chamber
- Method of conditioning air: no data
- System of generating particulates/aerosols: Institute´s dust generator with compressed air operating atomizer
- Temperature, humidity, pressure in air chamber: av. 21 - 23 °C, minimum 19.1, max. 25.4 °C /
65 - 75 % rel. humidity, during extreme weather occasionally up to 95.5 % or down to 48 %.
- Air flow rate: approx. 40 m3/h
- Air change rate: 40 / 2.3 = ~17/h
- Method of particle size determination: due to electrostatic charge of the particles not measured:
technical failure of the 10-stage Mercer cascade impactor and the QCM cascade (Report p. 16)
- Treatment of exhaust air: filtered before release


TEST ATMOSPHERE
- Brief description of analytical method used: gravimetrically - Air samples are drawn through glass fiber filters (Sartorius)
and weighed (3 - 4 time per day)
- Samples taken from breathing zone: no data

Duration and frequency of treatment / exposure:

90 day(s)

Remarks:

Doses / Concentrations:
35 mg/m3 (mean analytical values)

No. of animals per sex per dose / concentration:

10 each after exposure (13 weeks) and recovery period (1, 13, 29, 39, and 52 wks):
i.e. 50 m / 50 f animals per group were kept for a recovery period of at most 52 wks 

Control animals:

yes, concurrent no treatment

Positive control reference chemical:

no, but comparative study also including quartz

Details on study design:

- Dose selection rationale: see 7.5.3

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion) of SiO2
- Tissues and body fluids sampled: lung and mediastinal lymph nodes
- Time and frequency of sampling: 1, 13, 29, 39, and 52 weeks post exposure, 10 animals each

Statistics:

The statistical assessment of the findings for the different parameters considered was based on analysis of variance (ANOVA) and Dunnett´s test

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: ca. 7 wks (males) (from lung, see Table below)

Test no.:

#2

Toxicokinetic parameters:

half-life 2nd: <7 wks (females) (from lung, see Table below)

Metabolites identified:

not measured

Absolute silicon content in lung and mediastinal lymph nodes 1, 13, 29, 39, and 52 weeks post exposure

[Sipernat 22S, 35 mg/m³ (mean analytical value), 13 weeks] [Report, Tab. 59 + 61]

	Lung [mg]		Lymphnodes [mg]
	Male #1	Female #2	Male	Female
Sipernat 22S
Day 98	0.510 ±0.024 ^+) (n=10)^++)	0.347 ±0.017 (n=10)	0.037 ±0.007 (n=3)	0.034 ±0.002 (n=5)
Day 188	0.127 ±0.011  (n=10)	0.114 ±0.006 (n=7)	0.030 ±0.000 (n=2)	0.050 ±0.004 (n=4)
Day 297	0.049 ±0.004   (n=10)	0.083 (n=1)	0.027 ±0.003 (n=4)	0.030 (n=1)
Day 370	No Si detected	No Si detected	0.030 ±0.000 (n=2)	No Si detected
Day 462	No Si detected	No Si detected	0.030 (n=1)	No Si detected
C ontrol [untreated]
Day 188	0.032 (n=1)	No Si detected	0.030 (n=1)	No Si detected

⁺⁾ ±SEM (Standard Error of the Mean)

^{++) n represents the number of animals with Si found,}

^{the total number of animals measured was always 10 per group.}

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results

Reference 6

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Objective of study:

absorption

excretion

Qualifier:

no guideline followed

Principles of method if other than guideline:

modification of the method of Hemenway et al. (s. below)

GLP compliance:

not specified

Radiolabelling:

no

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

Weight at study initiation: 200 - 250 g

Route of administration:

inhalation: dust

Details on exposure:

TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 300-L horizontal laminar-flow chamber, compartmentalised
- System of generating particulates/aerosols: screw-feed mechanism (ACCURate, Whitewater) in combination with a Venturi-type dust feeder
- Temperature, humidity, pressure in air chamber:
- Air flow rate:
- Air change rate:
- Method of particle size determination: no data


TEST ATMOSPHERE
- Brief description of analytical method used: no data
- Samples taken from breathing zone: no data

Duration and frequency of treatment / exposure:

13 wks, 6 h/d, 5 d/wk

Dose / conc.:

50.4 mg/m³ air (analytical)

Remarks:

50.4 +/- 19.0

No. of animals per sex per dose / concentration:

4 animals for analysis

Control animals:

yes, concurrent no treatment

Positive control reference chemical:

quartz [Cristobalite] (3 mg/m3, crystalline)

Details on study design:

Post-exposure period: 3 and 8 months

Details on absorption:

755.9 +/- 22.9 µg/lung were detected after 6.5 weeks of treatment, and 882.7 +/- 83.1 µg/lung after 13 weeks

Details on excretion:

The silica content per lung after 3 and 8 months of recovery was 156.0 +/- 38.6 µg and 92.6 +/- 38.6 mg, respectively. About 82% and 89% were therefore excreted within 3 and 8 months, respectively.

Metabolites identified:

no

Lung burdens after subchronic exposure of rats to SAS and crystalline silica (µg SiO₂/lung) (Report Tab. 1)

	Weeks of exposure		Weeks after exposure (recovery)
	6.5	13	12	32
Control	55.9 ±40.4	42.5 ±16.9	28.1 ±13	39.8 ±8.7
SAS, 50 mg/m^3	755.9 ±22.9*	882.7 ±83.1*	156.0 ±38.6*	92.6 ±38.6
Cristobalite, crystalline 3 mg/m^3	335.6 ±28.3*	819.0 ±83.3*	657.6 ±28*	743.0 ±14.5*

Values represent the arithmetic means ±SD; n = 4 rats/treatment

* significantly different from age-matched control group: p < 0.05

Conclusions:

755.9 +/- 22.9 µg/lung after 6.5 weeks of treatment; 882.7 +/- 83.1 µg/lung after 13 weeks of treatment.
Ca. 82% and 89% excretion within 3 and 8 months of recovery, repectively.

Executive summary:

This is part of a comparative study including synthetic amorphous and crystalline silica. Here only the absorption and excretion of Aerosil 200 (amorphous) are documented.

Reference 7

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, sufficiently documented, acceptable for assessment

Objective of study:

other: retention and clearance from lung

Qualifier:

no guideline available

GLP compliance:

no

Specific details on test material used for the study:

various silicas: Quartz, corundum, AEROSIL 150

Radiolabelling:

no

Species:

rat

Strain:

other: Albino

Sex:

female

Route of administration:

inhalation: dust

The average one-day retention value was 28 ug/lung at the lower concentration 

(not specified). 
During the first 10 days, a steep linear increase was seen with about 28 ug/day 

as theoretically expected; thereafter, increments became significantly smaller, 

suggesting that elimination increased and that an equilibrium between retention 

and elimination was established (p. 427).

After 40 exposures, the average one-day retention value was 59 ug/lung at 

the high concentration (40-50 mg/m3, see p. 431). 

After 120 exposures, the total deposit (lung and mediastinal lymph nodes) was 

found to be only at 435 ug/lung, equivalent to 7.4 % of the theoretically 

deposited material (5840 ug/lung, based on the measured one-day retentions), 

ie. more than 92 % of the deposited SiO2 in the alveoles was eliminated during 

the exposure period. 
At that time, the mean retention of the lungs was only 300 ug/lung 

(= approx. 69 % of the total). 

The deposition rate in the mediastinal lymph nodes was negligible during the 

first 40 days, but was increasing gradually. 

After 120 exposures, the retention there was substantial amounting to some 

135 ug (about 31 % of the total deposit).

A test for the determination of free alveolar cells showed a decrease 

immediately after a single exposure and 24 hours later an increase of 100 % 

was seen.
  --------------

Conclusions:

After prolonged exposure of rats to high concentrations of
amorphous silica (40-50 mg/m3), overall elimination was high
without accumulation in the lung: only 5-6 % of respirable
(theoretically deposited) material was found after 120
exposure days. On the other hand, transfer to mediastinal
lymph nodes was substantial after prolonged exposure under
these conditions with about 31 % of total deposit = 1.5- 2 %
of the respirable (theoretically deposited) material. The
involvement of lymphatic elimination appears to be not
relevant after short exposure periods (here up to 40 times),
at least at lower body burden of amorphous silica.

[note: In other studies, higher retentions after 3 months
were found: 1.5 mg SiO2/lung for DOW CORNING silica (p. 431)
(see Schepers et al., 1957)].
------------

Reference 8

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study, containing scientifically justified modifications (see: Method).

Reason / purpose for cross-reference:

reference to same study

Objective of study:

other: solubility of amorphous silicas under physiological conditions

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 105

Radiolabelling:

no

Species:

other: not applicable

Route of administration:

other: in vitro, not applicable

Details on study design:

see Chapter 4.8

More details see 4.8 (Vogelsberger 2003/2004_solub_Silica, 37°C_key_RL1)

Saturation / equilibrium concentration in aqueous media (37 °C):

Product	Surface [BET, m^2/g]	Max. soluble fraction		Reference Vogelsberger [year]
		[mmol SiO2/L]	[mg SiO2/L]
HDK T40	376	2.70	162	2003; 2004
HDK T30	305	2.55	153	2003; 2004
Zeosil Z45	244; 192	2.30	138	2003; 2004
Zeosil Z11	103	1.27	76	2003
Cab-O-Sil M5	221; 203	2.35	141	2003; 2004
Aerosil 300	262	2.76	166	2003
Sipernat 320	183	2.29	137	2003
Syloid 74	313	2.11	127	2003

*) Note: Primary particles do not exist isolated.

The saturation concentrations for all analysed silicas were reached quickly within 5 to 10 h, in an exceptional case about 20 h. 
The saturation concentration increased with increasing specific surface area/of the corresponding silicas.

  ------------------

Influence of surfactant: 
DPPC had no significant effect on water solubility.
   -----------------

The maximal solubility of HDK T40 was approx. 2.5 - 2.7 mmol/l 

= approx. 150 - 160 mg/l(Vogelsberger 2003/2004).

The maximal solubility of Aerosil 300 was 2.76 mmol/l 

= 166 mg/l(Vogelsberger 2003)

  -----------------

There was no substantial difference in water solubility between the tested media.
  

Reference 9

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Objective of study:

absorption

distribution

excretion

Qualifier:

no guideline available

Principles of method if other than guideline:

Si analysis: Ammonium-molybdate method according to Stegemann H and Fitzek FJ (1956): Die mikroanalytische Bestimmung von Silizium in quarz- und silikathaltigen Staubproben. Aus der deutschen Forschung der letzten Dezennien. Thieme Verlag Stuttgart 1956

GLP compliance:

no

Specific details on test material used for the study:

HDK V 15

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

female

Details on test animals or test system and environmental conditions:

no data

Route of administration:

inhalation: dust

Duration and frequency of treatment / exposure:

6 and 18 weeks and 12 months ( Interim kill after 6 and 18 weeks)
5 h/d, 5x/wk initially, but later (time not stated) weekly frequency reduced to 2-3x/wk because suppurative bronchitis and severe inflammation caused losses.
Post exposure (recovery period): 5 months

Remarks:

Doses / Concentrations:
50 - 55 mg/m3 (nominal), respirable about 30 mg/m3 with aerodynamic diameter of =<7 µm

No. of animals per sex per dose / concentration:

in total 150 animals

Control animals:

not specified

Test no.:

#1

Toxicokinetic parameters:

other: 6 wks: Mean lung burden with SiO2: 0.5 mg

Test no.:

#1

Toxicokinetic parameters:

C(time): 6 wks: Mean burden with SiO2 (mediastinal lymph node): 0.02 mg

Test no.:

#2

Toxicokinetic parameters:

C(time): 18 wks: Mean lung burden with SiO2: 1.2 mg

Test no.:

#2

Toxicokinetic parameters:

C(time): 18 wks: Mean burden with SiO2 (mediastinal lymph node): 0.11 mg

Test no.:

#3

Toxicokinetic parameters:

C(time): 12 months: Mean lung burden with SiO2: 1.37 mg/lung

Test no.:

#3

Toxicokinetic parameters:

C(time): 12 months: Mean burden with SiO2 (mediastinal lymph node): 0.13 mg

Test no.:

#3

Toxicokinetic parameters:

other: 12 months: maximum lung burden approx 1 % of total dose

Test no.:

#4

Toxicokinetic parameters:

half-life 1st: approx 7 weeks (12 months exposure + 5 months recovery: SiO2 content lung: approx. 12 % of 12-months deposit)

Test no.:

#4

Toxicokinetic parameters:

other: 12 months exposure + 5 months recovery: SiO2 content in mediastenal lymph node: approx. 40 to 50 % of 12-months deposit

No substantial increase in the SiO2 deposition in the lung and the mediastinal lymph nodes were observed between exposure of 18 wks and of 12 months. About 90 % of the SiO2 was cleared from the lungs and 50 - 60 % from the mediastinal lymph nodes within 5 months. This corresponds to an approximate half-life time of 7 weeks, based on first-order elimination kinetics.

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
SiO2 in lungs: after 6wk = 0.5 mg, after 18wk = 1.2 mg, after 12m = 1.37 mg (= 1% of total exposure accumulated in lungs)

Executive summary:

A chronic inhalation study was performed to evaluate the toxicokinetics of HDK V 15.

Reference 10

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Objective of study:

absorption

Qualifier:

no guideline available

Principles of method if other than guideline:

absorption in inner organs: 1 dose level, 1 month administration

GLP compliance:

not specified

Specific details on test material used for the study:

Sipernat 700

Radiolabelling:

no

Species:

rat

Strain:

not specified

Remarks:

albino

Sex:

female

Details on test animals or test system and environmental conditions:

c. 160-185 g

Route of administration:

oral: gavage

Vehicle:

water

Duration and frequency of treatment / exposure:

daily for 1 month

Dose / conc.:

1 500 mg/kg bw/day (nominal)

No. of animals per sex per dose / concentration:

20 (females only)

Control animals:

yes

Details on absorption:

SiO2 content after 1 month of oral intake: liver 1.5 µg, kidneys 6.4 µg, spleen 5.3 µg
controls: liver 1.8 µg, kidneys 7.2 µg, spleen 7.8 µg

no effects on body weight, behaviour or food intake

Conclusions:

Livers, kidney and spleens did not show any absorption of the substance.

Executive summary:

The absorption to inner organs was evaluated in rats feed with Sipernat 700 for 1 month.

Reference 11

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Objective of study:

excretion

Qualifier:

no guideline available

Principles of method if other than guideline:

alveolar SiO2 concentraion levels after exposure and 1 / 2 / 3 months of recovery; one dose level

GLP compliance:

not specified

Specific details on test material used for the study:

Sipernat 700

Radiolabelling:

no

Species:

rat

Strain:

other: albino, inbred

Sex:

female

Route of administration:

inhalation: dust

Vehicle:

not specified

Dose / conc.:

60 mg/m³ air (nominal)

No. of animals per sex per dose / concentration:

40 (females only)

Control animals:

no

Details on study design:

inhalation: 3 days, 5 h/d
10 rats each were killed and the alveolar SiO2 content was measured 10 hours after treatment and after 1, 2 or 3 months of recovery.
[The study states that 100 rats were killed 10 h. after treatment, which is an obvious misprint, since there were only 40 rats in total.]

Details on excretion:

alveolar SiO2 concentration after 20 h / 1 / 2 / 3 months: 0.343 / 0.09 / 0.042 / 0.010 mg/lung
97 % eliminantion after 3 months
SiO2 concentration in lymph nodes after 1 / 2 / 3 months: 0.005 mg / 0.003 mg / 0.002 mg

Conclusions:

The elimination rate from lungs was 97% within 3 months.

Executive summary:

The elimination of inhalated Sipernat 700 was measured in rats.

Reference 12

Endpoint:

basic toxicokinetics, other

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1 week

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Objective of study:

distribution

Qualifier:

no guideline followed

Principles of method if other than guideline:

The particle size distribution of 3 SAS-products (HDK DO5, Sipernat 22S, Syloid 72W) suspended in physiological media containing lung surfactant was monitored over a period of 1 week. The particles size distribution was measured by laser difraction (LD) for mainly the micrometer range, dynamic light scattering (DLS) for mainly the submicrometer range and optical centrifugation analysis (OCA).

GLP compliance:

not specified

Specific details on test material used for the study:

HDK DO5 (Wacker/VK75725): pyrogenic silica, hydrophilic surface, grade BET 50m²/g
Sipernat 22S (Evonik/UB21352-1): precipitated silica, hydrophilic surface, grade 190m²/g
Syloid 72W (Grace/5084905): gel, hydrophilic surface, pores 1.2cm³/g

Radiolabelling:

no

Species:

other: in-chemico experiment

Details on test animals or test system and environmental conditions:

in-chemico experiment, no animals used
dipalmitoyl phosphatidyl-choline (DPPC), supplied by Sigma-Aldrich, in Dulbecco's phosphate buffered saline with Ca and Mg suitable for cell cultures was used as lung surfactant
the samples were stored at 37°C

Route of administration:

other: a suspension of SAS and DPPC in physiological media was prepared

Vehicle:

other: Dulbecco`s phosphate buffered saline

Details on exposure:

1 week exposure at 37°C

Dose / conc.:

2 400 ppm

Remarks:

ppm (weight)

Dose / conc.:

300 ppm

Remarks:

ppm (weight)

No. of animals per sex per dose / concentration:

none

Control animals:

yes, concurrent vehicle

Details on study design:

LD (size analysis by laser diffraction): in a 4ml glass cuvette, suspension stirred, measurements conducted at small scattering angles (approx. 0.1°... 9°), analysed by Fraunhofer's difraction theory, laser wavelenght 632.8 nm and refractive index set to water value (1.332), results refer to the volume weight size distribution.
DLS (size analysis by dynamic light scattering): 10 repeated runs, 90s measurement time, auto-correlation function were analysed by the method of cumulants and CONTIN-like conversion algorithm set to "general purpose", laser wavelenght 632.8nm, scattering angle 173°, for viscosity and refractive index of the continious phase water values (0.00069 Pa, 1.332) were used, results presented as intensity weighted distribution
OCA (size analysis by optical centrifugation analysis): Centrifugal speed for HDK DO5: 1500 rpm (approx. 300g), for Sipernat 22S: 300 rpm (approx. 12g), for Syloid 72W: 500 rpm (approx. 34g), the centrifuge was operated un til the transmission profiles reached a steady state, size distributions were calculated from tranmission-in-time curves from 2 cuvettes at 5 positions each time, for analysis water values (density 994 kg/m³, viscosity 0.00069 Pa) were used, particle density was set to be solid density (2200 kg/m³), aggregate porosity not considered, results are presented as extinction weighted distribution.

Details on dosing and sampling:

measurement after 0h, 3h, 6h, 1d, 2d, 3d, 4d, 5d, 6d

Statistics:

LD: average of 6 runs, DLS: average of 10 runs, OCA: 2 cuvettes at 5 positions

Preliminary studies:

none

Type:

other: deagglomeration of particles in lung surfactant

Results:

no active deagglomeration of SAS aggregates

Metabolites identified:

not measured

No evidence that SAS particles deagglomerate in physiological medium containing lung surfactant (DPPC)

Conclusions:

no deagglomeration in physiological medium containing lung surfactant (DPPC particles)

Description of key information

No substance accumulation of synthetic amorphous silica was observed in tissues following oral administration of synthetic amorphous silica.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

oral route:

The absorption to inner organs was evaluated in rats feed with synthetic amorphous silica (SAS) (Sipernat 700) for 1 month, which displayed no absorption of the substance in liver, kidney and spleen (no-Guideline study, Klosterkoetter,1968). The studies in rats showed no or only slight increase of SAS in liver and spleen. In Lang, 1966 the excretion of SiO₂was assessed in human probands. The urinary excretion of humans added up to less than 0.5% of the dose applied within 4 days. In 2012, as part of a CEFIC-LRI project, SAS (NM-200) was tested in an oral two-generation reproduction toxicity study according to OECD guideline 416. This material was used in 2018 for the evaluation of Si-distribution in organs and deposition-related tissue alterations. Dust particles remain located free on the surface of the gastrointestinal tract. There was no distribution to other organs found (Weber, 2018).

The literature describes SAS as biosoluble and therefore not biopersistent (Sohal et al. 2018). Roelofs and Vogelsberger (2004) concluded that “nanosized silica” particles show an increased solubility. The existence of special surface-active components (surfactant) does not show a significant influence on the dissolution behavior of such type of silica in biological-like media. Furthermore, the increased energy of these nano- particles is responsible for a relatively fast dissolution process and higher maximum silica concentrations observably. Lee et al. (2017) studied the solubility, absorption, tissue distribution and excretion kinetics of SAS (E 551) following single-dose oral administration to rats. The effect of the presence of food components, such as sugar and protein, on the absorption of nanoparticles was also evaluated by measuring silicon urinary excretion. Particle size was found to have no significant effect on in vivo dissolution, biodistribution or excretion kinetics. The absorption profile of SAS was highly dependent on the presence of sugar or protein, showing an accelerated absorption rate in the presence of glucose, presumably due to a surface interaction on nanoparticles. In the scientific opinion “Re-evaluation of silicon dioxide (E 551) as a food additive“, the EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) reviewed studies limited on food grades SAS (E551). The Panel summarizes that by using different model fluids mimicking the various steps of the GIT, it was shown that the proportion of nanosized silicon dioxide which may be released from the food is dependent on the conditions in the GIT (pH, electrolyte concentration, etc.), on the initial content of nanoparticles in the sample added to the food, and on the form of the food (EFSA ANS Panel, 2018).

 

dermal route:

The dermal route is not a relevant exposure route for systemic exposure. Intended skin exposure is assessed under the cosmetic regulation.

 

inhalation route:

 The information was summarized by an external expert as follows (Dekant and Colnot 2014):

 

>>After inhalation exposure (5 h/d) of rats to 50 mg/m³(respirable fraction) of a hydrophilic SAS (pyrogenic HDK® V15) for three days, mean levels of 0.25 mg SiO₂were found in the lungs. SiO2 was not detected in mediastinal lymph nodes 20 hours after the end of the exposure. After one month, only 0.105 mg SiO₂was left in the lung and 0.018 mg SiO₂in lymph nodes. After three month, lungs contained 0.018 mg SiO₂and lymph nodes contained 0.008 mg SiO₂. Thus, mean SiO₂levels in lungs decreased by 58% within one month and by 93% within three months (Klosterkötter, 1969).

During exposure (5 h/d, 5 d/wk) of rats to 50 to 55 mg/m³(total dust; approximately 30 mg/m³of respirable particles) of a hydrophilic SAS (pyrogenic HDK® V15) for 12 months, app. 0.5 mg SiO₂was present in lungs after six weeks, 1.2 mg after 18 weeks, and 1.37 mg after 12 months. After 12 months, it was estimated that only app. 1 % of administered particles were retained in the lungs. Thus, lung deposition increased rapidly upon initial exposure and then decreased between week 18 and week 52. The mediastinal lymph nodes contained app. 0.02 mg SiO₂after six weeks, 0.11 mg after 18 weeks, and 0.13 mg after 12 months. After five months of recovery, mean residual levels of SiO₂were 0.16 mg in lungs and 0.047 mg in lymph nodes indicating a reduction of 88 % in the lung burden and more than 50 % in lymph nodes (Klosterkötter, 1969).

In a comparative study with three hydrophilic SAS (precipitated Zeosil® 45, gel SYLOID® 74 and pyrogenic CAB-O-SIL® M-5), Wistar rats (10/sex/group) were exposed (6 h/d) for five days to target concentrations of 1, 5, and 25 mg SAS/m³, respectively. Satellite groups were exposed under identical conditions and analyzed after a recovery period of one or three months. Crystalline silica (quartz, 25 mg/m³) was used as positive control. One day after exposure, 30 to 40 μg Si (64- 86 μg SiO₂) was detected in lungs of high dose animals after Zeosil® 45 exposure, 76 μg Si (163 μg SiO₂, mean value) after SYLOID® 74 exposure and 43 μg Si (92 μg SiO₂, mean value) after CAB-O-SIL® M-5 fumed silica exposure. After the exposure-free period, the Si content of the lungs was below the detection limit (15-30 μg Si) with all SAS except for one unexplained observation of the presence of Zeosil® 45 after three months. By comparison, in quartz exposed animals, Si accumulation was four to five times higher (150 - 160 μg; 320 - 340 μg SiO₂) and Si levels remained high after recovery periods of one (80 μg in females, 140 μg in males; 171 or 300 μg SiO₂) or three months (110 μg in females, 130 μg in males; 240 or 280 μg SiO₂). Si levels in lungs of animals exposed to the lower concentrations of SAS and in tracheobronchial lymph nodes of all exposed animals were below the detection limit (Arts and Kuper, 2003a,b; Arts et al., 2003). <<