Fumes, silica

Endpoint summary

Description of key information

Repeated dose inhalation toxicity studies with synthetic amorphous silica by Reuzel et al. (1991), Groth et al. (1981) and Artz et al. (2007) show mainly reversible lung effects. Human information on the silicon/ferrosilicon/synthetic amorphous silica manufacturing industry shows only effects attributable to general dust exposure.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

chronic toxicity: oral

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 452 (Chronic Toxicity Studies)

GLP compliance:

not specified

Species:

other: mice and rats

Strain:

other: B6C3F1 mice and Fisher rats

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Funabashifarm Animal Co. Ltd, Japan
- Age at study initiation: mice 4 weeks, rats 3 weeks
- Weight at study initiation: male-mice 21.0-27.3 g, female-mice 16.0-19.9 g; male-rats 117-150 g, female-rats 92.0- 126 g
- Fasting period before study:
- Housing: in wire-mesh cages, separated according to sex, 5 mice per cage, 2 rats per cage
- Diet (e.g. ad libitum):
- Water (e.g. ad libitum): tap water ad lipidum
- Acclimation period: 1 week for mice; 2 weeks for rats


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23.1+-1
- Humidity (%): 50+-10
- Air changes (per hr): air-conditioned
- Photoperiod (hrs dark / hrs light): artifical fluorescent lighting daily for a continuous 14-hour period


IN-LIFE DATES: From: To:

Route of administration:

oral: feed

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:


DIET PREPARATION
- Rate of preparation of diet (frequency): prepared weekly
- Mixing appropriate amounts with (Type of food):
- Storage temperature of food:


VEHICLE
- Justification for use and choice of vehicle (if other than water):
- Concentration in vehicle:
- Amount of vehicle (if gavage):
- Lot/batch no. (if required):
- Purity:

Duration of treatment / exposure:

93 weeks for mice and 103 weeks for rats

Frequency of treatment:

daily

Remarks:

Doses / Concentrations:
0, 1.25, 2.5, 5%
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
0, 2500, 5000, 10000 mg/kg bw/day (for mice)
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
0, 625, 1250, 2500 mg/kg bw/day (for rats)
Basis:
nominal in diet

No. of animals per sex per dose:

mice and rats were dined into dosage groups of 10 animals each

Control animals:

yes

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily for survival
- Cage side observations checked in table [No.?] were included.


DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:

BODY WEIGHT: Yes
- Time schedule for examinations: with mice 0, 5, 15, 30, 50, 81 and 93 weeks after feeding; with rats 0, 5, 15, 30, 50, 81 and 103 weeks after feeding


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes / No / No data
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes / No / No data


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes / No / No data


WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes / No / No data
- Time schedule for examinations:


OPHTHALMOSCOPIC EXAMINATION: No
- Time schedule for examinations:
- Dose groups that were examined:


HAEMATOLOGY: Yes
- Time schedule for collection of blood: 6, 12 and 21 months for mice and 6, 12 and 24 months for rats
- Anaesthetic used for blood collection: Yes (identity) / No / No data
- Animals fasted: Yes / No / No data
- How many animals: 89/160 male mice and 105/158 female mice; 118/161 male rats and 123/161 female rats
- Parameters checked in table [No.?] were examined: erythrocytes (RBC), hemoglobin (Hb), leucocytes (WBC) and hematocrit (Ht)


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 6, 12 and 21 (mice) or 24 (rats) months
- Animals fasted: Yes / No / No data
- How many animals: 89/160 male mice and 105/158 female mice; 118/161 male rats and 123/161 female rats
- Parameters checked in table [No.?] were examined: aspartate transaminase (AST), alanine transaminase (ALT), serum inorganic phosphorus (IP), total protein (TP), albumin (ALB), lactic dehydrogenase (LDH), alkali phosphatase (ALP), total bilirubin (TB), total cholesterol (T-Cho), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triglyceride (TG), blood urea nitrogen (BUN), uric acid (UA), creatine (Cre), and calcium (CA) on serum separated from the blood after clotting


URINALYSIS: No
- Time schedule for collection of urine:
- Metabolism cages used for collection of urine: Yes / No / No data
- Animals fasted: Yes / No / No data
- Parameters checked in table [No.?] were examined.


NEUROBEHAVIOURAL EXAMINATION: No
- Time schedule for examinations:
- Dose groups that were examined:
- Battery of functions tested: sensory activity / grip strength / motor activity / other:


OTHER:

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

Statistics:

The mean and standard deviations of various measured parameters were calculated for each dose group. The significant difference between the control and the compound-treated groups was tested by Student's t-analysis variance test (P<0.05*; P<0.01**). The chi-square test of significance (P<0.05) by Mantel-Hanszel was employed to compare the survival date exclusive of sacrificed specimens. Prevalence rates were cited as percentages of tumor groups and non-tumor groups in cases of post-mortem examination. The significance of differences between the two means of prevalence was tested by Fisher's exact test for fourfold tables. The percentages of the frequencies of tumor in specific tissues were analysed by the Cochrane-Armitage test for linear trend in proportion with continuity correction.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS AND MORTALITY:
Most of the mice remained in good health, appeared to be active, and showed normal behavior throughout the treatment. No significant difference in survival rates for each group was observed.
In rats, no physical or behavioral signs of pharmacologic effects were observed during the treatment. In male rats over a perioid of 48 weeks, the mean survival rates in treated groups was greatest in the 5%, followed by the control and 1.25 or 2.5% dosage groups. However, the variations were not significant between the control and treated groups. While the female survival rates of 5%, 2.5%, and 1.25% groups were 0.875, 0.80, and 0.65 respectively, these were not statisticall and significantly different from the values observed in the control group.

BODY WEIGHT AND WEIGHT GAIN:
In mice, during the initial 61-week period, the control and treated groups grew at essentially the same rate. No significant variation in body weight were observed throughout this study between the control and treated groups of 1.25% and 2.5% dosages. However, at the end of the initial 10-week period, the 5% dosage group showed lower growth rate as compared to the control group. At 81 weeks, an increase in food consumption in the control groups was evident in the treated male groups of 2.5% and 5% dosages. Increased food consumption in the treated group of 5% dosage was accompanied by decreased body weight.
In rats, no consistent compound- or dose-related changes in growth rates were evident.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
In mice, the mean cumulative intake of SYLOID at the end of 93 weeks in the 1.25, 2.5 and 5% dietary levels was 38.45, 79.78 and 160.23 g/mouse in males, and 37.02, 72.46 and 157.59 g/mouse in females, respectively.
In rats, the mean cumulative intake of SYLOID at the end of 103 weeks for the 1.25, 2.5 and 5% dietary levels was 143.46, 179.55 and 581.18 g/rat in males, and 107.25, 205.02 and 435.33 g/rat in females, respectively.


FOOD EFFICIENCY

HAEMATOLOGY:
In mice, the mean HCT and MCV at 12 months in female mice showed a somewhat lower level in comparison with the normal group. However, there was no evidence of dose-related alteration of hematological profiles at the end of the 12- and 21-month treatments.
In rats, occasional erratic variations in hematologic profiles were observed in the treated groups: high WBC at 24 months in male groups of 1.25% dosage, and low RBC, HGB, and HCT at 24 months in the female 2.5% dosage group. The very high value for WBC in male rats of the 1.25% group looks as if it has one or two values, perhaps because of technical errors. However, no significance can be attached to the difference.

CLINICAL CHEMISTRY: In rats, no biologically meaningful changes in TA, ALB, AST, ALT, ALP, T-BL and LDH were observed, although transient differences reaching statistical significance were frequently present. No noteworthy changes related to compound ingestion were observed in any parameters of renal analyses, such as BUN, CRE and UA.

ORGAN WEIGHTS: No noted atrophy or hypertrophy of the organs in each group was sex- or dose-related.


GROSS PATHOLOGY


HISTOPATHOLOGY: NON-NEOPLASTIC:
In mice, non-neoplastic lesions were observed in the subcutis, lungs, kidneys, and liver in the treated groups. These were considered to be of no toxicological significance.

HISTOPATHOLOGY: NEOPLASTIC (if applicable):
In mice, tumours attributed to the treatment of Syloid were found in the hematopoietic organs, particularly malignant lymphoma/leuiemia, which occurred in 7/20 (35%) in the female groups of the 2.5% dosage groups (not scientifically significant). In the lungs, the frequency of adenoma/adenocarcinoma was 1/16 (6.25%) for the control, 2/17 (11.8%) for the 1.25%, 3/14 (21.4%) for the 2.5% and 3/16 (18.8%) for the 5% dosage groups of males. The incidence of the lung adenomas in females was greater than that of males. However, none of these findings were sex- or dose-related. In the liver, the correlation of hyperplasic nodules/hepato cellular carcinoma/hemangioma/fibrosarcoma in the treated groups, as compared with the control group, was relatively low.
In rats, the incidence of tumors was the greatest in the genital organs, next in the skin. The other organs showed relatively low incidence.
The occasional presence of some neoplasms did not reveal any consistent, dose-related trends in any group.


HISTORICAL CONTROL DATA (if applicable)


OTHER FINDINGS

Dose descriptor:

NOAEL

Remarks:

the highest dose tested

Effect level:

10 000 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: for mice; Syloid

Dose descriptor:

NOAEL

Remarks:

the highest dose tested

Effect level:

2 500 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: for rats; Syloid

Critical effects observed:

not specified

Conclusions:

Proper dietary administration of micronized silica (Syloid 244) was proven to be generally safe with no long-term effects.

Executive summary:

Food-grade micronized silica gel (SYLOID®) was given in a feed to B6C3F1 mice and Fisher rats at dose levels of 0, 1.25, 2.5, and 5% (≈ 0, 2,500, 5,000, 10,000 mg/kg/day for mice and 0, 625, 1,250, 2,500 mg/kg/day for rats), for 93 weeks and 103 weeks, respectively (Takizawa et al. 1988). Measurements: physical examinations and observations, clinical chemistry, post-mortem examination. There were no biological or any other meaningful alterations in the body weight, food consumption or physical features of the exposed animals. No significant dose-related effects were seen at any dose level upon clinical laboratory examinations. The pathological examinations revealed no gross or microscopic changes in the tissues examined. The occasional presence of some neoplasms did not reveal any consistent, dose-related trends in any group.

Reference 2

Endpoint:

repeated dose toxicity: oral

Type of information:

other: OECD evaluation of unpublished in vivo studies

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: A scientific evaluation by an authoritative international body. Read-across to synthetic amorphous silica.

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

OECD evaluated the available test data on synthetic amorphous silica.

GLP compliance:

no

Species:

rat

Route of administration:

other: oral feed and gavage

Dose descriptor:

NOAEL

Effect level:

4 000 - 4 500 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: hydrophilic precipitated silica, sub-chronic study; 4000-4500 mg/(kg*d) = 6.7%

Dose descriptor:

NOAEL

Effect level:

8 980 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: hydrophilic silica gel, sub-chronic study

Critical effects observed:

not specified

Conclusions:

OECD (2004) includes eight sub-acute or sub-chronic repeated oral toxicity studies with synthetic amorphous silica, of which two are regarded as critical studies for SIDS endpoint. In these critical studies, NOAEL of 4000-4500 mg/kg bw/d (for hydrophilic precipitated silica) and 8980 mg/kg bw/day (for hydrophilic silica gel) were reported.

Executive summary:

An OECD report (2004) found that, after long-term oral application (sub-chronic or sub-acute) in the diet, no adverse effects were demonstrable for synthetic amorphous silica.

 

Reference 3

Endpoint:

repeated dose toxicity: oral, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

No toxicological data were available for silica fume and, therefore, a read-across approach was used. The dissolution, composition and surface properties were the most important parameters considered when deciding which substances can be used for read-across.

Based on the composition, surface characteristics, and bioaccessibility data, silica fume was assumed to have toxicological properties similar to those of sparingly synthetic amorphous silicas. Therefore read-across was carried out using available toxicological studies with synthetic amorphous silica (SAS).

Details on the read-across approach are presented in Iuclid section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Remarks on result:

other: No effects observed

Critical effects observed:

no

Conclusions:

No adverse effects documented in reports on repeated dose oral exposure to synthetic amorphous silica.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

other: OECD 412

Qualifier:

according to guideline

Guideline:

other: OECD GLP

GLP compliance:

yes

Remarks:

TNO Committee on Animal Welfare

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland (Sulzfeld, Germany)
- Age at study initiation: young adult
- Housing: under conventional laboratory conditions in suspended, stainless steel cages fitted with wire mesh floor and front
- Diet (e.g. ad libitum): powdered RM3 rodent diet
- Water (e.g. ad libitum): unfluoridated tap water ad libidum
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22+-3
- Humidity (%): at least 30, not exceeding 70
- Air changes (per hr): about 10 air changes per hour
- Photoperiod (hrs dark / hrs light):

IN-LIFE DATES: From: To:

Route of administration:

inhalation: dust

Type of inhalation exposure:

nose only

Remarks on MMAD:

MMAD / GSD: 1-4 μm

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: inhalation units (ADG Developments Ltd. Codicote, Herts, UK)
- Method of holding animals in test chamber: During exposure, the rats were individually restrained in Battelle tubes and each tube was then placed into one of the inhalation units for head/nose-only exposure to the test atmosphere.
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: Zeosil 45 - using a miniatyre screw conveyor to a low velocity eductor in which the test material was aerolised; Syloid 74 and Cab-O-Sil M5 - electromagnetically driven, miniatyre dust feeders were used that released periodiacally small lumps of test material to low velocity eductors in which the test materials were aerolised
- Temperature, humidity, pressure in air chamber: The temperature and the relative humidity were recorded 4-5 times during each exposure day (Testo Bmbh & Co., Lenzkirch, Germany).
- Air flow rate: 51 L/min (3060 L/h) for a 50-L unit to 98 L/min (5880 L/h) for a 80-L unit
- Air change rate:
- Method of particle size determination: Particle size distribution was measured twice a day using an aerodynamic particle sizer (APS, TSI Inc., St. Paul, MN, USA).
- Treatment of exhaust air:


TEST ATMOSPHERE
- Brief description of analytical method used: Gravimetric analysis using sampling flows of 4.4.-5 l/min. The actual concentrations were calculated by dividing the amount of test material present on each fibre glass filter by the volume of the respective sample taken. The number of samples taken werere generally 3-5 per exposure day for 25 mg/m3 athmosphere, 3 for 5 mg/m3 athmosphere and 1 for 1 mg/m3 athmosphere.
- Samples taken from breathing zone: yes


VEHICLE (if applicable)
- Justification for use and choice of vehicle:
- Composition of vehicle:
- Type and concentration of dispersant aid (if powder):
- Concentration of test material in vehicle:
- Lot/batch no. of vehicle (if required):
- Purity of vehicle:

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

5 days

Frequency of treatment:

6 hours/day

Remarks:

Doses / Concentrations:
1, 5, 25 mg/m3
Basis:
nominal conc.

No. of animals per sex per dose:

for Zeosil 45 and quartz, and for respective controls, 10 rats per sex; for Syloid 74 and Cab-O-Sil M5, 10 males in each exposure group, and for controls 12 males

Control animals:

yes

Details on study design:

- Rationale for animal assignment (if not random): For the Syloid 74 and Cab-O-Sil M5 exposures, only male rats were used because of a slightly higher sensitivity in male rats when compared to female rats in the initial experiments with Zeosil 45 and quartz.

Positive control:

Crystalline silica (25 mg/m3)

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: prior to the first exposure, on day 5, at weekly intervals threafter and on the day of scheduled necropsy

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

FOOD EFFICIENCY: No data
WATER CONSUMPTION: No
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: No
CLINICAL CHEMISTRY: No
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No

OTHER:
- bronchoalveolar lavage (BAL) and measurements (total protein, albumin, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), N-acetyl-glucosaminidase (NAG), superoxide dismutase (SOD) and tumour necrose factor alpha (TNF-alpha), as well as additionally glutathione in Zeosil 45 treatment
- hydroxyproline content

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table)
HISTOPATHOLOGY: Yes (see table)

Statistics:

Body weight data were analysed by one-way analysis of co-variance (ANCOVA) using pre-exposure (day 0) weights as the covariate. Total cell counts, absolute differential cell counts and biochemical parameters in BALf, silicon content in lungs and lymph nodes, and weights of these organs were analysed by one-way analysis of variance (ANOVA). When group means were significantly different, individual pairwise comparisons were made using Dunnett's multiple comparison method. However, when variances were grossly unequal, separate comparisons were made, i.e. between groups exposed to SAS (including the control group; ANOVA-Dunnett) and between the reference and control group (Student t-test). Relative differential BALf cell counts were analysed by Kruskal-Wallis non-parametric ANOVA followed by Mann-Whitney U-test. Also, when variances were grossly unequal, separate comparisons were made, i.e. between groups exposed to SAS (including the control group) and between the reference and control group. The incidences of histopathological changes were analysed by Fisher's exact probability test. All pairwise comparisons were two-tailed. Group mean differences with an associated probability of less than 0.05 were considered to be statistically significant.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY:
No treatment-related clinical signs were observed except for a slightly decreased breathing frequency visually observed during exposure to Zeosil 45 and quartz. It was transient in animals expsoed to Zeosil 45, and persistent in animals of the quartz group.

BODY WEIGHT AND WEIGHT GAIN:
A slight though statistically significant body weight loss was observed in all groups to Cab-O-Sil M5 the day after the last exposure. Due to absence of a concentration-response relationship, this finding was not considered to be test compound-related. No changes during the other SAS and quartz exposures.

FOOD CONSUMPTION:
No changes in food intake.
CLINICAL CHEMISTRY
Induced elevations in cytotoxicity biomarkers in BAL fluid at 5 and 25 mg/m3.

ORGAN WEIGHTS
Increases in lung and tracheobronchial lymph node weight at 25 mg/m3.

GROSS PATHOLOGY:
None of the groups exhibited treatment-related gross lesions at necropsy.

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathological changes in the lungs and tracheobronchial lymph nodes were observed. Most changes were at 25 mg/m3 and to a lesser degree at 5 mg/m3, and none at 1 mg/m3. Directly after the exposure period, the histopathological changes in the lungs that were observed consisted of increased intra-alveolar accumulation of macrophages (SYLOID® 74 and Cab-OSil M5) and granulocytes (Zeosil® 45 and Cab-O-Sil® M5), and bronchial/bronchiolar hypertrophy (all SAS; Tables 3-5).
All of these changes were very slight to slight. No changes were observed in the tracheobronchial lymph nodes. After the 1-month post-exposure period, accumulation of alveolar macrophages and a few macrophage accumulation of macrophages (Zeosil® 45 and Cab-O-Sil® M5) and granulocytes (Zeosil® 45), mononuclear cell infiltrate (Zeosil® 45), bronchial/bronchiolar hypertrophy (Zeosil® 45), bronchiolar-alveolar epithelial hyperplasia with interstitial infiltration of macrophages (Zeosil® 45), and overfilled septal capillaries (hyperaemia; Zeosil® 45) were observed in the lungs. The tracheobronchial lymph nodes exhibited aggregates of macrophages, which were comparable in size and number with those observed at the 1-month post-exposure period (Cab-O-Sil® M5). The macrophage aggregates were seen in all animals exposed to 25 mg/m3 Cab-O-Sil® M5.
Effects were transient and, with the exception of slight histopathological changes at the higher exposure levels, were reversible during the 3-month recovery period.


HISTOPATHOLOGY: NEOPLASTIC (if applicable)


HISTORICAL CONTROL DATA (if applicable)


OTHER FINDINGS

Dose descriptor:

NOAEL

Effect level:

1 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: synthetic amorphous silica

Critical effects observed:

not specified

With quartz-exposed animals the presence of silicon in the lungs was persistent and toxicological effects differed from those seen with synthetic amorphous silicas both with regard to the type and severity as well as in the time-response profile. One-day post-exposure to quartz, elevations in biomarkers of cytotoxicity in BAL fluid, increases in lung and tracheobronchial lymph node weight and histopathological lung changes were minimal. These effects were present at 1-month post-exposure and progressively more severe at 3-months post-exposure.

Executive summary:

In a 5-day inhalation toxicity study by Arts et al. (2007), rats were exposed to 1, 5 or 25 mg/m³ of synthetic amorphous silica and to 25 mg/m³ of quartz. There were no serious clinical effects, and no changes in body weight or food intake. No adversed effects were observed with the exposure to amorphous silica at 1 mg/m³. There were induced elevations in cytotoxicity biomarkers in BAL fluid at 5 and 25 mg/m³, and increases in lung and tracheobronchial lymph node weight at 25 mg/m³. Histopathological changes were observed at 5 and 25 mg/m³. The effects were transient with amorphous silica, and, with the exception of slight histopathological lung changes at the higher exposure levels, also reversible during the 3-month recovery period.

Reference 2

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 452 (Chronic Toxicity Studies)

GLP compliance:

not specified

Species:

other: rat, guinea pig and monkey

Strain:

other: Sprague-Dawley rats, Hartley guinea pigs, and Cynomolgus monkeys

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Laboratory Supply Company, Inc., Indianapolis, Ind. (rats), Sweetwater Farms, Hillsboro, Ohio (guine pigs), Primate Imports Corp., Long Island, N.Y. (monkeys)
- Age at study initiation: adult monkeys
- Weight at study initiation: 300-380 g (rats), 400-800 g (guinea pigs), 2300-5400 g (monkeys)
- Fasting period before study:
- Housing: all three species individually housed during the exposures, rats and guine pigs two to four animals per cage at all other times
- Diet (e.g. ad libitum): standard laboratory pellet diets (Rodent Laboratory Chow, Guinea Pig Chow, and Monkey Chow-Jumbo from Ralston Purina, St. Louis, Mo.); monkeys were given fresh fruit (oranges, bananas, or apples) twice a week
- Water (e.g. ad libitum): tap water ad libidum
- Acclimation period: rats and guinea pis were quarantined for two weeks, monkeys for one month


ENVIRONMENTAL CONDITIONS
- Temperature (°C):
- Humidity (%):
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light):


IN-LIFE DATES: From: To:

Route of administration:

inhalation: dust

Type of inhalation exposure:

whole body

Remarks on MMAD:

MMAD / GSD: Amount of particles <4.7 μm: 65% (pyrogenic silica), 62% (silica gel), 46% (precipitated silica)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel inhalation chamber 60 in. long by 57 in. wide by 57 in. high (160ft3)
- Method of holding animals in test chamber: stainless and galvanized steel open wire-mesh cages were used as exposure cageing to provide adequate distribution of the dust aerosols within the exposure chambers
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: Silica gel and precipitated silica dust aerosols were generated by Wright dust feed mechanisms, which were affixed to each exposure chamber. Fume silica was generated with a modified fluidized bed.
- Temperature, humidity, pressure in air chamber:
- Air flow rate: dynamic flow conditions with tangential airfeed manifolds maintained at 40 L/min with a pressure pf -0.254 cm H2O
- Air change rate:
- Method of particle size determination:
- Treatment of exhaust air:


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


VEHICLE (if applicable)
- Justification for use and choice of vehicle:
- Composition of vehicle:
- Type and concentration of dispersant aid (if powder):
- Concentration of test material in vehicle:
- Lot/batch no. of vehicle (if required):
- Purity of vehicle:

Duration of treatment / exposure:

up to 18 months

Frequency of treatment:

5.5-6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
15 mg/m3
Basis:

No. of animals per sex per dose:

80 rats/dose, 20 guinea pigs/dose, 10 monkeys/dose

Control animals:

yes

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes / No / No data
- Time schedule:
- Cage side observations checked in table [No.?] were included.


DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:


BODY WEIGHT: Yes / No / No data
- Time schedule for examinations:


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes / No / No data


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes / No / No data


WATER CONSUMPTION: Yes / No / No data
- Time schedule for examinations:


OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood:
- Anaesthetic used for blood collection: Yes (identity) / No / No data
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood:
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.


URINALYSIS: Yes / No / No data
- Time schedule for collection of urine:
- Metabolism cages used for collection of urine: Yes / No / No data
- Animals fasted: Yes / No / No data
- Parameters checked in table [No.?] were examined.


NEUROBEHAVIOURAL EXAMINATION: No

OTHER: Pulmonary function in monkeys was tested prior the study.

Sacrifice and pathology:

Autopsies on rats were performed after 3, 6 and 12 months of exposure, and on guinea pigs and monkeys after 10 to 18 months of exposure.

Statistics:

Multivariate one-way analyses of covariance between the control and each exposed group were calculated. The dependent variables (pulmonary functions) were placed into two groups for this analysis. The ventilatory mechanisms group included resistance at low frequency (RLLF), compliance at low frequency (CLLF), forced expiratory flow at 25 percent vital capacity (FEF25), forced expiratory flow at 10 percent vital capacity (FEF10%), closing volume (CV), nitrogen washout (N2), and volume of isoflow (VISFL). The lung volume group included forced vital capacity (FVC), inspiratory capacity (IC), residual volume (RV), and total lung capacity (TLC). If the multivariate analysis indicated a significant difference, then each response variable was analyzed individually by adjusted univariate analysis.

Body weight and weight changes:

not examined

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY

BODY WEIGHT AND WEIGHT GAIN

HAEMATOLOGY
No statistically significant changes.

CLINICAL CHEMISTRY
No statistically significant changes in rats and guinea pigs. Alkaline phosphatase levels in fume silica monkeys were elevated compared to controls (however, elevation did not correlate with pathology and was probably not the result of exposure).

ORGAN WEIGHTS

GROSS PATHOLOGY

HISTOPATHOLOGY: NON-NEOPLASTIC
The most significant finding was the deposition of large quantities of amorphous silica in macrophages in the lungs and tracheal lymph nodes of exposed monkeys. Regardless of the type of amorphous silica to which they were exposed, the lungs of each monkey contained large numbers of macrophage and mononuclear cell aggregates. The size of cell aggregates varied from 40 to 600 μm in diameter and they were found in the walls of respiratory bronchioles, alveolar ducts, around venules and arterioles, and occasionally in alveolar walls distant from the aforementioned structures. More and larger aggregates appeared in the lungs exposed to precipitated silica, slightly fewer and smaller ones in the lungs exposed to fumed silica, and considerably fewer and smaller ones in the lungs exposed to silica gel. Relatively few or no macrophages containing particles of amorphous silica were found in the lungs and lymph nodes of the guinea pigs and rats. Fumed silica induced early nodular fibrosis in the lungs of the monkeys, 5– 50% of the aggregates contained collagen in varying amounts in six of the nine monkeys exposed to fumed silica. In three of the monkeys, little or no collagen was present in the aggregates.

HISTOPATHOLOGY: NEOPLASTIC (if applicable)

HISTORICAL CONTROL DATA (if applicable)

OTHER FINDINGS
Lung-function studies indicated statistically significant differences in lung volume and ventilatory mechanics between the monkeys exposed to fumed silica and the control group. In addition, monkeys exposed to precipitated silica demonstrated significantly lower lung volumes compared with controls, while monkeys exposed to silica gel had significant changes in ventilatory performance and mechanical properties.

Dose descriptor:

LOAEL

Effect level:

15 mg/m³ air

Sex:

male

Basis for effect level:

other: rat, monkey; for respirable particles (<4.7 μm) about 6 to 9 mg/m³

Critical effects observed:

not specified

Executive summary:

In a chronic inhalation study of Groth et al. (1981), rats, guinea pigs, and monkeys were exposed by inhalation for up to 18 months to fume, gel and precipitated synthetic amorphous silica. The concentration used was 15 mg/m³ and the exposure was performed 5.5 to 6 h/day, 5 days/week. Exposure with monkeys showed the most significant findings: deposition of amorphous silica in macrophages in the lungs and tracheal lymph nodes, induction of early nodular fibrosis in the lungs, and differences in lung volume and ventilatory mechanics measurements between exposed and controls. LOAEL for amorphous silica was 15 mg/m³ (total dust).

Reference 3

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Principles of method if other than guideline:

Prior to subchronic 13-week study, a 2-week concentration-finding study was performed

GLP compliance:

not specified

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: TNO Central Institute for the Breeding of Laboratory Animaqls
- Age at study initiation: 4 weeks in sub-acute study; 6 weeks in sub-chronic study
- Weight at study initiation:
- Fasting period before study:
- Housing: singly in stainless-steel wire cages in Hazleton H 1000 inhalation chambers
- Diet (e.g. ad libitum): Institute's stock diet for rats
- Water (e.g. ad libitum): unfluoritated tap-water ad libidum
- Acclimation period:


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-23
- Humidity (%): 65-75
- Air changes (per hr): 40 m3/hr
- Photoperiod (hrs dark / hrs light):


IN-LIFE DATES: From: To:

Route of administration:

inhalation: dust

Type of inhalation exposure:

whole body

Remarks on MMAD:

MMAD / GSD: Mean primary particle sizes were 12 nm for Aerosil® 200 and Aerosil® R974, 18 nm for Sipernat® 22S and 8000 nm for quartz. The range of the geometric agglomerate/aggregate size distribution was 1-120 μm for the amorphous silicas with maxima at about 10 and 100 μm. Quartz particle sizes globally varied between 0.1 and 25 μm.

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus:
- Method of holding animals in test chamber: inhalation chamber
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: Aerosols were genearated using the Institue's dust generators, which were composed of a dust feed mechanism and an atomizer operated by compressed air.
- Temperature, humidity, pressure in air chamber:
- Air flow rate:
- Air change rate:
- Method of particle size determination:
- Treatment of exhaust air:


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


VEHICLE (if applicable)
- Justification for use and choice of vehicle:
- Composition of vehicle:
- Type and concentration of dispersant aid (if powder):
- Concentration of test material in vehicle:
- Lot/batch no. of vehicle (if required):
- Purity of vehicle:

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentrations of test material in the test atmospheres were determined by gravimetry. Samples of the test atmospheres were drawn through glass fibre filters (Sartorius SM 13430). The filters were weight just before and after sampling.

Duration of treatment / exposure:

2 weeks in sub-acute concentrtion-finding study, 13 weeks in sub-chronic study

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
1, 6, 30 mg/m3 (Aerosil® 200)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
1.3, 5.9, 31 mg/m3 (Aerosil® 200)
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
30 mg/m3 (Aerosil® R974)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
30 mg/m3 (Sipernat® 22S)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
60 mg/m3 (quartz)
Basis:
nominal conc.

No. of animals per sex per dose:

70

Control animals:

yes

Details on study design:

- Dose selection rationale: Prior to 13-week subchronic study, a 2-week concentration-finding study was performed. Doses tested in this study were: 0, 17, 44 or 164 mg/m3 air with Aerosil 200; 0, 31, 87 or 209 mg/m3 air with Aerosil R974; 0, 46, 180 or 668 mg/m3 air with Sipernat 22S; and 0, 70, 211 or 901 mg/m3 air with quartz dust.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION: No data

FOOD EFFICIENCY: No data

WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: Yes
- Time schedule for collection of blood:
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 rats/sex/group
- Parameters examined: Cell counts, haemoglobin content, packed cell volume, white-cell counts, differential white-cell counts, prothrombin time, thrombocytes, albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, urea, total protein, creatinine, total bilirubin, calcium, potassium, sodium, inorganic phosphatase, cholesterol and glucose

CLINICAL CHEMISTRY: Yes / No / No data
- Time schedule for collection of blood:
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.

URINALYSIS: Yes
- Time schedule for collection of urine:
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters examined: Appearance, volume, density and pH, analysis for protein, occult blood, glucose and ketones, and microscopy of sediment

NEUROBEHAVIOURAL EXAMINATION: No data

OTHER:

Sacrifice and pathology:

After the exposure period and 13, 26, 39 and 52 wk after exposure 20, 10, 10, 10 and 20 rats/sex/group, respectively, were killed.

Other examinations:

Pathology; collagen contents in lungs and silicon content in lungs and associated lymph nodes

Statistics:

Body weights were analysed by an analysis of co-variance followed by the Dunnett's multiple comparison test. Analysis of variance followed by the Dunnet's multiple comparison test were applied to the organ weights, and haematological and biochemical data. Incidences of histopathological changes were analysed by the Fisher exact probability test.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

not examined

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY
During the 13-wk exposure, there was a concentration-related increase in the respiration rate of animals exposed to Aerosil® 200. The respiration rate quickly returned to normal when the exposure was ended.

All test materials induced increases in lung weight, and pulmonary lesions such as accumulation of alveolar macrophages, inflammation, alveolar bronchiolization and fibrosis. In addition, rats exposed to Aerosil® 200, Aerosil® R954 or quartz developed granulomatous lesions. Silicosis was observed only in quartz-exposed animals. At the end of the exposure period, Aerosil® 200 and quartz had induced the most severe changes.


BODY WEIGHT AND WEIGHT GAIN
At the end of the exposure period, body-weight gain was 5-10% lower in males exposed to 30 mg Aerosil® 200/m3 or 30 mg Sipernat® 22S/m3. After a 13-wk post-exposure, these changes had returned to normal. The quartz-exposed rats showed a slightly progressive reduction in weight gain throughout the post-exposure period.

HAEMATOLOGY
Neutrophilic leukocyte counts were significantly elevated in rats exposed to 30 mg/m3 of Aerosil® 200 and 60 mg/m3 of quartz. The changes were reversible with Aerosil 200 but not with quartz. Red blood cell counts, haemoglobin content and packed cell volumes slightly increased in males exposed to 30 mg Aerosil® 200/m3, Aerosil® R974 or quartz by the end of the exposure. After 13 wk and further, the males exposed to quartz remained to show high red blood cell values.

CLINICAL CHEMISTRY
Alanine aminotransferase activities increased in quartz-exposed rats 13 wk and alkaline phosphatise activity 52 wk after exposure.

URINALYSIS
Urine analyses were essentially negative.

ORGAN WEIGHTS
All test materials induced increases in lung weight.

GROSS PATHOLOGY


HISTOPATHOLOGY: NON-NEOPLASTIC
With Aerosil 200, dose-related changes caused by inflammatory reactions and irritation of the tissue were observed in the lung of animals. Associated lesions only partly recovered during the one-year post-exposure period at the top exposure level. The level of 1.3 mg/m3 induced only slight changes, which generally recovered quickly (cellular infiltration, stimulation of collagen production and increase in lung weight). Focal interstitinal fibrosis was not noted directly after the exposure period of 3 months, but appeared with a delay in the 30-mg rats, and to a lesser degree, in the 6-mg group. Treatment-related, microscopic changes in the nasal region were occasionally found at the end of the exposure period such as focal necrosis and slight atrophy of the olfactory epithelium. After 13 wk at 1.3 mg/m3, there was no morphological tissue effects that could be considered as a pathological manifestation (slight reversible collagen stimulation and no significant increase in lung weight).

HISTOPATHOLOGY: NEOPLASTIC (if applicable)


HISTORICAL CONTROL DATA (if applicable)


OTHER FINDINGS

Dose descriptor:

NOAEL

Effect level:

< 17 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: sub-acute (2-week), Aerosil 200

Dose descriptor:

NOAEL

Effect level:

< 31 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: sub-acute (2-week), Aerosil R 974

Dose descriptor:

NOAEL

Effect level:

< 46 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: sub-acute (2-week), Sipernat 22S

Dose descriptor:

NOAEL

Effect level:

1.3 mg/m³ air (analytical)

Sex:

male/female

Basis for effect level:

other: sub-chronic (13-week), Aerosil 200

Critical effects observed:

not specified

Executive summary:

Reuzel et al. (1991) studied sub-chronic inhalation toxicity of amorphous silica and quartz by exposing rats to test substances in a 13-week inhalation study. Only quartz induced progressive lesions in the lungs resembling silicotic nodules. Among the amorphous silicas fumed hydrophilic Aerosil® 200 induced the most severe changes in the lungs, which only partly recovered, whereas precipitated Sipernat® 22S induced the least severe, completely reversible lung changes.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

other: OECD 412

Qualifier:

according to guideline

Guideline:

other: OECD GLP

GLP compliance:

yes

Remarks:

TNO Committee on Animal Welfare

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland (Sulzfeld, Germany)
- Age at study initiation: young adult
- Housing: under conventional laboratory conditions in suspended, stainless steel cages fitted with wire mesh floor and front
- Diet (e.g. ad libitum): powdered RM3 rodent diet
- Water (e.g. ad libitum): unfluoridated tap water ad libidum
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22+-3
- Humidity (%): at least 30, not exceeding 70
- Air changes (per hr): about 10 air changes per hour
- Photoperiod (hrs dark / hrs light):

IN-LIFE DATES: From: To:

Route of administration:

inhalation: dust

Type of inhalation exposure:

nose only

Remarks on MMAD:

MMAD / GSD: 1-4 μm

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: inhalation units (ADG Developments Ltd. Codicote, Herts, UK)
- Method of holding animals in test chamber: During exposure, the rats were individually restrained in Battelle tubes and each tube was then placed into one of the inhalation units for head/nose-only exposure to the test atmosphere.
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: Zeosil 45 - using a miniatyre screw conveyor to a low velocity eductor in which the test material was aerolised; Syloid 74 and Cab-O-Sil M5 - electromagnetically driven, miniatyre dust feeders were used that released periodiacally small lumps of test material to low velocity eductors in which the test materials were aerolised
- Temperature, humidity, pressure in air chamber: The temperature and the relative humidity were recorded 4-5 times during each exposure day (Testo Bmbh & Co., Lenzkirch, Germany).
- Air flow rate: 51 L/min (3060 L/h) for a 50-L unit to 98 L/min (5880 L/h) for a 80-L unit
- Air change rate:
- Method of particle size determination: Particle size distribution was measured twice a day using an aerodynamic particle sizer (APS, TSI Inc., St. Paul, MN, USA).
- Treatment of exhaust air:


TEST ATMOSPHERE
- Brief description of analytical method used: Gravimetric analysis using sampling flows of 4.4.-5 l/min. The actual concentrations were calculated by dividing the amount of test material present on each fibre glass filter by the volume of the respective sample taken. The number of samples taken werere generally 3-5 per exposure day for 25 mg/m3 athmosphere, 3 for 5 mg/m3 athmosphere and 1 for 1 mg/m3 athmosphere.
- Samples taken from breathing zone: yes


VEHICLE (if applicable)
- Justification for use and choice of vehicle:
- Composition of vehicle:
- Type and concentration of dispersant aid (if powder):
- Concentration of test material in vehicle:
- Lot/batch no. of vehicle (if required):
- Purity of vehicle:

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

5 days

Frequency of treatment:

6 hours/day

Remarks:

Doses / Concentrations:
1, 5, 25 mg/m3
Basis:
nominal conc.

No. of animals per sex per dose:

for Zeosil 45 and quartz, and for respective controls, 10 rats per sex; for Syloid 74 and Cab-O-Sil M5, 10 males in each exposure group, and for controls 12 males

Control animals:

yes

Details on study design:

- Rationale for animal assignment (if not random): For the Syloid 74 and Cab-O-Sil M5 exposures, only male rats were used because of a slightly higher sensitivity in male rats when compared to female rats in the initial experiments with Zeosil 45 and quartz.

Positive control:

Crystalline silica (25 mg/m3)

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: prior to the first exposure, on day 5, at weekly intervals threafter and on the day of scheduled necropsy

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

FOOD EFFICIENCY: No data
WATER CONSUMPTION: No
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: No
CLINICAL CHEMISTRY: No
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No

OTHER:
- bronchoalveolar lavage (BAL) and measurements (total protein, albumin, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), N-acetyl-glucosaminidase (NAG), superoxide dismutase (SOD) and tumour necrose factor alpha (TNF-alpha), as well as additionally glutathione in Zeosil 45 treatment
- hydroxyproline content

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table)
HISTOPATHOLOGY: Yes (see table)

Statistics:

Body weight data were analysed by one-way analysis of co-variance (ANCOVA) using pre-exposure (day 0) weights as the covariate. Total cell counts, absolute differential cell counts and biochemical parameters in BALf, silicon content in lungs and lymph nodes, and weights of these organs were analysed by one-way analysis of variance (ANOVA). When group means were significantly different, individual pairwise comparisons were made using Dunnett's multiple comparison method. However, when variances were grossly unequal, separate comparisons were made, i.e. between groups exposed to SAS (including the control group; ANOVA-Dunnett) and between the reference and control group (Student t-test). Relative differential BALf cell counts were analysed by Kruskal-Wallis non-parametric ANOVA followed by Mann-Whitney U-test. Also, when variances were grossly unequal, separate comparisons were made, i.e. between groups exposed to SAS (including the control group) and between the reference and control group. The incidences of histopathological changes were analysed by Fisher's exact probability test. All pairwise comparisons were two-tailed. Group mean differences with an associated probability of less than 0.05 were considered to be statistically significant.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY:
No treatment-related clinical signs were observed except for a slightly decreased breathing frequency visually observed during exposure to Zeosil 45 and quartz. It was transient in animals expsoed to Zeosil 45, and persistent in animals of the quartz group.

BODY WEIGHT AND WEIGHT GAIN:
A slight though statistically significant body weight loss was observed in all groups to Cab-O-Sil M5 the day after the last exposure. Due to absence of a concentration-response relationship, this finding was not considered to be test compound-related. No changes during the other SAS and quartz exposures.

FOOD CONSUMPTION:
No changes in food intake.
CLINICAL CHEMISTRY
Induced elevations in cytotoxicity biomarkers in BAL fluid at 5 and 25 mg/m3.

ORGAN WEIGHTS
Increases in lung and tracheobronchial lymph node weight at 25 mg/m3.

GROSS PATHOLOGY:
None of the groups exhibited treatment-related gross lesions at necropsy.

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathological changes in the lungs and tracheobronchial lymph nodes were observed. Most changes were at 25 mg/m3 and to a lesser degree at 5 mg/m3, and none at 1 mg/m3. Directly after the exposure period, the histopathological changes in the lungs that were observed consisted of increased intra-alveolar accumulation of macrophages (SYLOID® 74 and Cab-OSil M5) and granulocytes (Zeosil® 45 and Cab-O-Sil® M5), and bronchial/bronchiolar hypertrophy (all SAS; Tables 3-5).
All of these changes were very slight to slight. No changes were observed in the tracheobronchial lymph nodes. After the 1-month post-exposure period, accumulation of alveolar macrophages and a few macrophage accumulation of macrophages (Zeosil® 45 and Cab-O-Sil® M5) and granulocytes (Zeosil® 45), mononuclear cell infiltrate (Zeosil® 45), bronchial/bronchiolar hypertrophy (Zeosil® 45), bronchiolar-alveolar epithelial hyperplasia with interstitial infiltration of macrophages (Zeosil® 45), and overfilled septal capillaries (hyperaemia; Zeosil® 45) were observed in the lungs. The tracheobronchial lymph nodes exhibited aggregates of macrophages, which were comparable in size and number with those observed at the 1-month post-exposure period (Cab-O-Sil® M5). The macrophage aggregates were seen in all animals exposed to 25 mg/m3 Cab-O-Sil® M5.
Effects were transient and, with the exception of slight histopathological changes at the higher exposure levels, were reversible during the 3-month recovery period.


HISTOPATHOLOGY: NEOPLASTIC (if applicable)


HISTORICAL CONTROL DATA (if applicable)


OTHER FINDINGS

Dose descriptor:

NOAEL

Effect level:

1 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: synthetic amorphous silica

Critical effects observed:

not specified

With quartz-exposed animals the presence of silicon in the lungs was persistent and toxicological effects differed from those seen with synthetic amorphous silicas both with regard to the type and severity as well as in the time-response profile. One-day post-exposure to quartz, elevations in biomarkers of cytotoxicity in BAL fluid, increases in lung and tracheobronchial lymph node weight and histopathological lung changes were minimal. These effects were present at 1-month post-exposure and progressively more severe at 3-months post-exposure.

Executive summary:

In a 5-day inhalation toxicity study by Arts et al. (2007), rats were exposed to 1, 5 or 25 mg/m³ of synthetic amorphous silica and to 25 mg/m³ of quartz. There were no serious clinical effects, and no changes in body weight or food intake. No adversed effects were observed with the exposure to amorphous silica at 1 mg/m³. There were induced elevations in cytotoxicity biomarkers in BAL fluid at 5 and 25 mg/m³, and increases in lung and tracheobronchial lymph node weight at 25 mg/m³. Histopathological changes were observed at 5 and 25 mg/m³. The effects were transient with amorphous silica, and, with the exception of slight histopathological lung changes at the higher exposure levels, also reversible during the 3-month recovery period.

Reference 2

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 452 (Chronic Toxicity Studies)

GLP compliance:

not specified

Species:

other: rat, guinea pig and monkey

Strain:

other: Sprague-Dawley rats, Hartley guinea pigs, and Cynomolgus monkeys

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Laboratory Supply Company, Inc., Indianapolis, Ind. (rats), Sweetwater Farms, Hillsboro, Ohio (guine pigs), Primate Imports Corp., Long Island, N.Y. (monkeys)
- Age at study initiation: adult monkeys
- Weight at study initiation: 300-380 g (rats), 400-800 g (guinea pigs), 2300-5400 g (monkeys)
- Fasting period before study:
- Housing: all three species individually housed during the exposures, rats and guine pigs two to four animals per cage at all other times
- Diet (e.g. ad libitum): standard laboratory pellet diets (Rodent Laboratory Chow, Guinea Pig Chow, and Monkey Chow-Jumbo from Ralston Purina, St. Louis, Mo.); monkeys were given fresh fruit (oranges, bananas, or apples) twice a week
- Water (e.g. ad libitum): tap water ad libidum
- Acclimation period: rats and guinea pis were quarantined for two weeks, monkeys for one month


ENVIRONMENTAL CONDITIONS
- Temperature (°C):
- Humidity (%):
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light):


IN-LIFE DATES: From: To:

Route of administration:

inhalation: dust

Type of inhalation exposure:

whole body

Remarks on MMAD:

MMAD / GSD: Amount of particles <4.7 μm: 65% (pyrogenic silica), 62% (silica gel), 46% (precipitated silica)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel inhalation chamber 60 in. long by 57 in. wide by 57 in. high (160ft3)
- Method of holding animals in test chamber: stainless and galvanized steel open wire-mesh cages were used as exposure cageing to provide adequate distribution of the dust aerosols within the exposure chambers
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: Silica gel and precipitated silica dust aerosols were generated by Wright dust feed mechanisms, which were affixed to each exposure chamber. Fume silica was generated with a modified fluidized bed.
- Temperature, humidity, pressure in air chamber:
- Air flow rate: dynamic flow conditions with tangential airfeed manifolds maintained at 40 L/min with a pressure pf -0.254 cm H2O
- Air change rate:
- Method of particle size determination:
- Treatment of exhaust air:


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


VEHICLE (if applicable)
- Justification for use and choice of vehicle:
- Composition of vehicle:
- Type and concentration of dispersant aid (if powder):
- Concentration of test material in vehicle:
- Lot/batch no. of vehicle (if required):
- Purity of vehicle:

Duration of treatment / exposure:

up to 18 months

Frequency of treatment:

5.5-6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
15 mg/m3
Basis:

No. of animals per sex per dose:

80 rats/dose, 20 guinea pigs/dose, 10 monkeys/dose

Control animals:

yes

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes / No / No data
- Time schedule:
- Cage side observations checked in table [No.?] were included.


DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:


BODY WEIGHT: Yes / No / No data
- Time schedule for examinations:


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes / No / No data


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes / No / No data


WATER CONSUMPTION: Yes / No / No data
- Time schedule for examinations:


OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood:
- Anaesthetic used for blood collection: Yes (identity) / No / No data
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood:
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.


URINALYSIS: Yes / No / No data
- Time schedule for collection of urine:
- Metabolism cages used for collection of urine: Yes / No / No data
- Animals fasted: Yes / No / No data
- Parameters checked in table [No.?] were examined.


NEUROBEHAVIOURAL EXAMINATION: No

OTHER: Pulmonary function in monkeys was tested prior the study.

Sacrifice and pathology:

Autopsies on rats were performed after 3, 6 and 12 months of exposure, and on guinea pigs and monkeys after 10 to 18 months of exposure.

Statistics:

Multivariate one-way analyses of covariance between the control and each exposed group were calculated. The dependent variables (pulmonary functions) were placed into two groups for this analysis. The ventilatory mechanisms group included resistance at low frequency (RLLF), compliance at low frequency (CLLF), forced expiratory flow at 25 percent vital capacity (FEF25), forced expiratory flow at 10 percent vital capacity (FEF10%), closing volume (CV), nitrogen washout (N2), and volume of isoflow (VISFL). The lung volume group included forced vital capacity (FVC), inspiratory capacity (IC), residual volume (RV), and total lung capacity (TLC). If the multivariate analysis indicated a significant difference, then each response variable was analyzed individually by adjusted univariate analysis.

Body weight and weight changes:

not examined

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY

BODY WEIGHT AND WEIGHT GAIN

HAEMATOLOGY
No statistically significant changes.

CLINICAL CHEMISTRY
No statistically significant changes in rats and guinea pigs. Alkaline phosphatase levels in fume silica monkeys were elevated compared to controls (however, elevation did not correlate with pathology and was probably not the result of exposure).

ORGAN WEIGHTS

GROSS PATHOLOGY

HISTOPATHOLOGY: NON-NEOPLASTIC
The most significant finding was the deposition of large quantities of amorphous silica in macrophages in the lungs and tracheal lymph nodes of exposed monkeys. Regardless of the type of amorphous silica to which they were exposed, the lungs of each monkey contained large numbers of macrophage and mononuclear cell aggregates. The size of cell aggregates varied from 40 to 600 μm in diameter and they were found in the walls of respiratory bronchioles, alveolar ducts, around venules and arterioles, and occasionally in alveolar walls distant from the aforementioned structures. More and larger aggregates appeared in the lungs exposed to precipitated silica, slightly fewer and smaller ones in the lungs exposed to fumed silica, and considerably fewer and smaller ones in the lungs exposed to silica gel. Relatively few or no macrophages containing particles of amorphous silica were found in the lungs and lymph nodes of the guinea pigs and rats. Fumed silica induced early nodular fibrosis in the lungs of the monkeys, 5– 50% of the aggregates contained collagen in varying amounts in six of the nine monkeys exposed to fumed silica. In three of the monkeys, little or no collagen was present in the aggregates.

HISTOPATHOLOGY: NEOPLASTIC (if applicable)

HISTORICAL CONTROL DATA (if applicable)

OTHER FINDINGS
Lung-function studies indicated statistically significant differences in lung volume and ventilatory mechanics between the monkeys exposed to fumed silica and the control group. In addition, monkeys exposed to precipitated silica demonstrated significantly lower lung volumes compared with controls, while monkeys exposed to silica gel had significant changes in ventilatory performance and mechanical properties.

Dose descriptor:

LOAEL

Effect level:

15 mg/m³ air

Sex:

male

Basis for effect level:

other: rat, monkey; for respirable particles (<4.7 μm) about 6 to 9 mg/m³

Critical effects observed:

not specified

Executive summary:

In a chronic inhalation study of Groth et al. (1981), rats, guinea pigs, and monkeys were exposed by inhalation for up to 18 months to fume, gel and precipitated synthetic amorphous silica. The concentration used was 15 mg/m³ and the exposure was performed 5.5 to 6 h/day, 5 days/week. Exposure with monkeys showed the most significant findings: deposition of amorphous silica in macrophages in the lungs and tracheal lymph nodes, induction of early nodular fibrosis in the lungs, and differences in lung volume and ventilatory mechanics measurements between exposed and controls. LOAEL for amorphous silica was 15 mg/m³ (total dust).

Reference 3

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Principles of method if other than guideline:

Prior to subchronic 13-week study, a 2-week concentration-finding study was performed

GLP compliance:

not specified

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: TNO Central Institute for the Breeding of Laboratory Animaqls
- Age at study initiation: 4 weeks in sub-acute study; 6 weeks in sub-chronic study
- Weight at study initiation:
- Fasting period before study:
- Housing: singly in stainless-steel wire cages in Hazleton H 1000 inhalation chambers
- Diet (e.g. ad libitum): Institute's stock diet for rats
- Water (e.g. ad libitum): unfluoritated tap-water ad libidum
- Acclimation period:


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-23
- Humidity (%): 65-75
- Air changes (per hr): 40 m3/hr
- Photoperiod (hrs dark / hrs light):


IN-LIFE DATES: From: To:

Route of administration:

inhalation: dust

Type of inhalation exposure:

whole body

Remarks on MMAD:

MMAD / GSD: Mean primary particle sizes were 12 nm for Aerosil® 200 and Aerosil® R974, 18 nm for Sipernat® 22S and 8000 nm for quartz. The range of the geometric agglomerate/aggregate size distribution was 1-120 μm for the amorphous silicas with maxima at about 10 and 100 μm. Quartz particle sizes globally varied between 0.1 and 25 μm.

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus:
- Method of holding animals in test chamber: inhalation chamber
- Source and rate of air:
- Method of conditioning air:
- System of generating particulates/aerosols: Aerosols were genearated using the Institue's dust generators, which were composed of a dust feed mechanism and an atomizer operated by compressed air.
- Temperature, humidity, pressure in air chamber:
- Air flow rate:
- Air change rate:
- Method of particle size determination:
- Treatment of exhaust air:


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


VEHICLE (if applicable)
- Justification for use and choice of vehicle:
- Composition of vehicle:
- Type and concentration of dispersant aid (if powder):
- Concentration of test material in vehicle:
- Lot/batch no. of vehicle (if required):
- Purity of vehicle:

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentrations of test material in the test atmospheres were determined by gravimetry. Samples of the test atmospheres were drawn through glass fibre filters (Sartorius SM 13430). The filters were weight just before and after sampling.

Duration of treatment / exposure:

2 weeks in sub-acute concentrtion-finding study, 13 weeks in sub-chronic study

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
1, 6, 30 mg/m3 (Aerosil® 200)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
1.3, 5.9, 31 mg/m3 (Aerosil® 200)
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
30 mg/m3 (Aerosil® R974)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
30 mg/m3 (Sipernat® 22S)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
60 mg/m3 (quartz)
Basis:
nominal conc.

No. of animals per sex per dose:

70

Control animals:

yes

Details on study design:

- Dose selection rationale: Prior to 13-week subchronic study, a 2-week concentration-finding study was performed. Doses tested in this study were: 0, 17, 44 or 164 mg/m3 air with Aerosil 200; 0, 31, 87 or 209 mg/m3 air with Aerosil R974; 0, 46, 180 or 668 mg/m3 air with Sipernat 22S; and 0, 70, 211 or 901 mg/m3 air with quartz dust.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION: No data

FOOD EFFICIENCY: No data

WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: Yes
- Time schedule for collection of blood:
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 rats/sex/group
- Parameters examined: Cell counts, haemoglobin content, packed cell volume, white-cell counts, differential white-cell counts, prothrombin time, thrombocytes, albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, urea, total protein, creatinine, total bilirubin, calcium, potassium, sodium, inorganic phosphatase, cholesterol and glucose

CLINICAL CHEMISTRY: Yes / No / No data
- Time schedule for collection of blood:
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.

URINALYSIS: Yes
- Time schedule for collection of urine:
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters examined: Appearance, volume, density and pH, analysis for protein, occult blood, glucose and ketones, and microscopy of sediment

NEUROBEHAVIOURAL EXAMINATION: No data

OTHER:

Sacrifice and pathology:

After the exposure period and 13, 26, 39 and 52 wk after exposure 20, 10, 10, 10 and 20 rats/sex/group, respectively, were killed.

Other examinations:

Pathology; collagen contents in lungs and silicon content in lungs and associated lymph nodes

Statistics:

Body weights were analysed by an analysis of co-variance followed by the Dunnett's multiple comparison test. Analysis of variance followed by the Dunnet's multiple comparison test were applied to the organ weights, and haematological and biochemical data. Incidences of histopathological changes were analysed by the Fisher exact probability test.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

not examined

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY
During the 13-wk exposure, there was a concentration-related increase in the respiration rate of animals exposed to Aerosil® 200. The respiration rate quickly returned to normal when the exposure was ended.

All test materials induced increases in lung weight, and pulmonary lesions such as accumulation of alveolar macrophages, inflammation, alveolar bronchiolization and fibrosis. In addition, rats exposed to Aerosil® 200, Aerosil® R954 or quartz developed granulomatous lesions. Silicosis was observed only in quartz-exposed animals. At the end of the exposure period, Aerosil® 200 and quartz had induced the most severe changes.


BODY WEIGHT AND WEIGHT GAIN
At the end of the exposure period, body-weight gain was 5-10% lower in males exposed to 30 mg Aerosil® 200/m3 or 30 mg Sipernat® 22S/m3. After a 13-wk post-exposure, these changes had returned to normal. The quartz-exposed rats showed a slightly progressive reduction in weight gain throughout the post-exposure period.

HAEMATOLOGY
Neutrophilic leukocyte counts were significantly elevated in rats exposed to 30 mg/m3 of Aerosil® 200 and 60 mg/m3 of quartz. The changes were reversible with Aerosil 200 but not with quartz. Red blood cell counts, haemoglobin content and packed cell volumes slightly increased in males exposed to 30 mg Aerosil® 200/m3, Aerosil® R974 or quartz by the end of the exposure. After 13 wk and further, the males exposed to quartz remained to show high red blood cell values.

CLINICAL CHEMISTRY
Alanine aminotransferase activities increased in quartz-exposed rats 13 wk and alkaline phosphatise activity 52 wk after exposure.

URINALYSIS
Urine analyses were essentially negative.

ORGAN WEIGHTS
All test materials induced increases in lung weight.

GROSS PATHOLOGY


HISTOPATHOLOGY: NON-NEOPLASTIC
With Aerosil 200, dose-related changes caused by inflammatory reactions and irritation of the tissue were observed in the lung of animals. Associated lesions only partly recovered during the one-year post-exposure period at the top exposure level. The level of 1.3 mg/m3 induced only slight changes, which generally recovered quickly (cellular infiltration, stimulation of collagen production and increase in lung weight). Focal interstitinal fibrosis was not noted directly after the exposure period of 3 months, but appeared with a delay in the 30-mg rats, and to a lesser degree, in the 6-mg group. Treatment-related, microscopic changes in the nasal region were occasionally found at the end of the exposure period such as focal necrosis and slight atrophy of the olfactory epithelium. After 13 wk at 1.3 mg/m3, there was no morphological tissue effects that could be considered as a pathological manifestation (slight reversible collagen stimulation and no significant increase in lung weight).

HISTOPATHOLOGY: NEOPLASTIC (if applicable)


HISTORICAL CONTROL DATA (if applicable)


OTHER FINDINGS

Dose descriptor:

NOAEL

Effect level:

< 17 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: sub-acute (2-week), Aerosil 200

Dose descriptor:

NOAEL

Effect level:

< 31 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: sub-acute (2-week), Aerosil R 974

Dose descriptor:

NOAEL

Effect level:

< 46 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: sub-acute (2-week), Sipernat 22S

Dose descriptor:

NOAEL

Effect level:

1.3 mg/m³ air (analytical)

Sex:

male/female

Basis for effect level:

other: sub-chronic (13-week), Aerosil 200

Critical effects observed:

not specified

Executive summary:

Reuzel et al. (1991) studied sub-chronic inhalation toxicity of amorphous silica and quartz by exposing rats to test substances in a 13-week inhalation study. Only quartz induced progressive lesions in the lungs resembling silicotic nodules. Among the amorphous silicas fumed hydrophilic Aerosil® 200 induced the most severe changes in the lungs, which only partly recovered, whereas precipitated Sipernat® 22S induced the least severe, completely reversible lung changes.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

1.3 mg/m³

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Additional information

Oral repeated dose toxicity studies with synthetic amorphous silicon dioxide show that silicon ion does not cause systemic target organ toxicity after ingestion. Since the bioavailability of silica fume is likely to resemble the bioavailability of synthetic amorphous silicon dioxide (see section 5.1: Toxicokinetics), silicon is also likely to be of low toxicological activity after repeated oral exposure.

The inhalation toxicity of amorphous silicon dioxides has been widely studied. The reason for this has been the known fibrinogenic effects of crystalline silica. The most critical studies on the repeated dose of synthetic amorphous silica include studies by:

·       Groth et al. (1981), who reported early nodular fibrosis in the lungs and its effects on the lung function of monkeys with an LOAEL of 15 mg/m³, with pyrogenic silica corresponding to approximately 7-9 mg/m³of respirable particles <4.7μm MMAD).

·       Reuzel et al. (1991), who reported inflammation, granulomatous lesions and interstitial fibrosis after exposure to synthetic amorphous silicas, with hydrophilic pyrogenic silica being the most potent. However, as opposed to quartz, these changes were (mostly) reversible after the cessation of exposures. The NOAEC was 1.3 mg/m³, LOAEC 6 mg/m³. The primary particle size range was <6–45 nm, with a maximum aggregate/agglomerate size distribution of 10μm.

·       Arts et al. (2007), who reported transient histopathological and BAL changes in rats exposed to ≥5 mg/m³of pyrogenic silica for 5 consecutive days. While quartz caused progressive changes in the lungs, synthetic amorphous silica caused only transient changes, which were resolved during the three-month follow-up period. The MMAD varied between 1.2 and 3.5μm.

Based on these studies, the OECD SIDS (2004) on synthetic amorphous silicas resulted in the following conclusions: The inhalation of respirable particles of synthetic amorphous silica produces a time- and dose-related inflammation response of the lung tissue in animal studies. A thirteen-week exposure to an average concentration of 1.3 mg/m³of a pyrogenic amorphous silica resulted in mild reversible pro-inflammatory cell proliferation rather than a pathologically relevant tissue change. Given the low-grade severity of this common lung-tissue response, 1 mg/m³can be established as the NOAEC (sub-chronic, 13 weeks). The LOAEC was 5.9 mg/m³and the mid concentration produced clear signs of histopathological adverse effects (stimulation of collagen production, an increase in lung weight, incipient interstitial fibrosis, sligth focal atrophy in the olfactory epithelium). All of these effects were reversible following discontinuation of exposure. No lung-tissue effects were observed following an exposure of five days to 1 mg/m³of the same silica [NOEC (short-term)]. The LOAEC (5 d) was 5 mg/m³.

The actual risk of adverse lung effects in humans by synthetic amorphous silica is likely to be low since the particles tend to form aggregates and agglomerates with diameters of up to 250 µm. This results in a slightly less than 1% access of the inhaled particle mass in the thoracic or alveolar region. Silica fume, on the other hand, does not form aggregates, but it forms agglomerates with sizes mostly in the inhalable fraction, and only approximately 1-3% of the particles lie in the respiratory fraction.

There are no repeated dose toxicity data on silica fume and, therefore, the read-across from synthetic amorphous silica particles should be considered. The only animal studies on the respiratory effects of silica fume include the Swedish studies by Glømme (1965), Glømme (1966-67) and Swensson (1967). The lung lesions caused by silica fume, quartz and pyrogenic silica were compared in the study by Swensson in 1967. The results suggest that synthetic pyrogenic silica causes slightly more severe lung effects than silica fume. These effects, however, did not progress during the follow-up assessment of animals, whereas quartz caused progressive lesions. The elimination of quartz from the lungs of the animals was significantly lower than that of amorphous silicas: more than 50% of the amount of quartz injected was found in the lungs of the animals eight months after the exposure, whereas, in the case of pyrogenic silica, quartz-glass and silica fume, no more than 20-30% of the administered dose was found.In vitrodata on the dissolution kinetics of synthetic amorphous silica and silica fume support the similarity in dissolution of silica fume and synthetic amorphous silica, although there are slight differences in the dissolution kinetics (silica fume showing slightly lower dissolution). Some of these differences may be explained by the variation in particle surface area, which is ten times lower for silica fume.

Among the various forms of synthetic amorphous silicas, the pyrogenic silica is considered to be the best option for the health effect read across to silica fume, since its particle characteristics best resemble silica fume. It also seems to be the most potent synthetic amorphous silica for inducing lung lesions and, thus, represents the most conservative option. Pyrogenic silica produces lung lesions, which, unlike in the case of quartz, seem to be reversible after the cessation of exposure. Swensson’s results (1967), although very limited in methodology, provide support for read-across.

Early human reports suggested adverse respiratory effects, that is, "ferroalloy disease" associated with amorphous silica fumes formed during the process. This disease was characterized by fibrotic changes, which, however, seemed to regress when the exposure ceased. An association with metal fume fever was also suggested. Metal fume fever, in general, is known to be caused only by freshly generated metal fumes in heavy exposures. The metal fume fever certainly is not relevant for "aged" silica fume particles subject to registration. The aging of silica fume particles results in the saturation of surface with silanol groups and the formation of agglomerates. The particle size of the newly generated fumes is about 0.5 µm (MMAD, Koch 2005).

The pathology of reported cases of "ferroalloy disease" within the metallurgical industry is unclear - whether it is related to these freshly generated fumes and repeated attacks of metal fume fever or to amorphous silicon dioxide particles is unclear. The confounding factors also include the co-exposing agents, like crystalline silica, which is used as a raw material and found in workplace air.

No cases of "ferroalloy" disease have been reported anymore since the 1980s. There is, however, new data suggesting an increased prevalence of COPD and a decline in the lung function (FEV₁) of the workers in these plants. The latest studies by Johnsen and co-workers (e.g., Jonhsen et al. 2010) correlate these effects with cumulative dust exposure. Similar effects have been seen both in FeSi/Si metal and FeMn/SiMn/FeCr plants. Increasing evidence from other industries shows that COPD may be related to workplace exposure to dust, fumes and gases in general (Balmes et al. 2003; Hnizdo et al. 2002; Trupin et al. 2003; Bergdahl et al. 2004; Blanc et al. 2009). It has been estimated that for COPD a population attributable risk of 15-20% is caused by occupational dust/fumes (Balmes et al. 2003). It has also been suggested that crystalline silica exposures at levels lower than those causing silicosis cause COPD (Hnizdo and Vallyathan 2007). The increased risk of COPD reported within the metallurgical industry is very likely to be a general dust/fume exposure related phenomenon rather than a specific effect of silica fume.

Justification for classification or non-classification

In the case of silica fume, very few specific toxicological data on the repeated dose toxicity of silica fume is available. Consequently, data on synthetic amorphous silica, especially on pyrogenic silica, is used for read-across. Read-across is supported by in vitro dissolution data and early comparative intra-tracheal studies by Swensson (1967). Also, epidemiological studies provide useful data for the assessment.

Respirable pyrogenic silica particles (MMAD <5–10 µm) cause lung effects like inflammation, granulomatous lesions and interstitial fibrosis in animal tests. These are mostly resolved in the follow-up assessment. The NOAEC for these effects, derived from the study of Reuzel et al. (1991), is 1.3 mg/m³. LOAECs of 5-9 mg/m³have been identified in three most reliable studies described above (Reuzel et al. 1991; Groth et al. 1981 and Arts et al. 2007). For CLP STOT category 1 classification, significant toxic effects should be seen at dust/aerosol levels of less than 20 mg/m³in 90-day inhalation exposures in animals. Since the pulmonary effects seen in animals were mild and mostly transient at dose levels less than 20 mg/m³, category 1 criteria are not fulfilled. The respirable particles of pyrogenic silica (and thus silica fume) may fulfil STOT category 2 criteria, which are used for the substances with significant target organ toxicity at moderate dose levels (guidance values for aerosols 20-200 mg/m³). However, silica fume forms agglomerates whose size depends mostly on an inhalable fraction, with only a 1-3 wt% in respiratory fraction. When the respirable particles cause reversible lung effects at dose levels of approximately 5 mg/m³, in the case of commercial silica fume these effects are likely to be seen only at >20-fold higher dose levels, meaning dose levels of ≥100 mg/m³. Commercial silica fume is thus not considered to fulfil the classification criteria.

Epidemiological data from the ferrosilicon/silicon metal industry show a decline in lung function, which is associated with exposure to newly generated fumes/dust present in the workplace air. This same effect has also been seen in other industries, and it has been estimated that for COPD a population attributable risk of 15-20% is caused by occupational exposure to dust/fumes (Balmes et al. 2003). Based on the recent studies by Johnsen and co-workers (two studies in 2008; 2010), it seems that this effect is more like a general dust-related phenomena than a specific effect of silica fume.

Traces of quartz in commercial silica fume have been reported. Quartz is known to cause pneumoconiosis (silicosis) with pulmonary fibrosis. Respirable quartz fulfils the STOT cat 1 criteria. According to CLP/GHS classification criteria for mixtures, any mixture containing a STOT cat 1 substance ≥1 wt% should be classified as STOT cat 1 and 1-10 wt% as STOT cat 2. Since respirable quartz levels are below the cut-off limit of 1 wt%, no classification due to quartz is suggested.

Silicon carbide may be present in silica fume at levels of up to 5%. Silicon carbide is toxic to the lungs in its fibrous form but not as amorphous dust (for review, ACGIH. Silicon Carbide. Documentations of the Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices: American Conference of Governmental Industrial Hygienists; 2001). Silicon carbide fibres have not been shown to be present in silica fume.

Other elemental impurities, which are present at levels of >1% and which may be released from silica fume, are not classified as repeated dose toxicants and do not cause a need to consider the classification of silica fume. These include magnesium and zinc in particular, which are released at higher amounts from silica fume than from pyrogenic silica (Aerosil).

Orally, synthetic amorphous silica has been virtually non-toxic in repeated dose toxicity tests. Based on the similarities in dissolution in aqueous solutions, which suggests similar bioaccessibility, silica fume is considered to resemble synthetic amorphous silica in this respect.