Fumes, silica

Repeated dose toxicity: inhalation

Administrative data

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

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2007

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: OECD 412

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: OECD GLP

GLP compliance:

yes

Remarks:

TNO Committee on Animal Welfare

Test material

Test material information

Constituent 1

Reference substance name:

precipitated silica

IUPAC Name:

precipitated silica

Constituent 2

Reference substance name:

silica gel

IUPAC Name:

silica gel

Constituent 3

Reference substance name:

pyrogenic silica

IUPAC Name:

pyrogenic silica

Details on test material:

- Name of test material (as cited in study report): tradenames: Zeosil® 45 (precipitated silica), SYLOID® 74 (gelled silica), Cab-O-Sil® M5 (pyrogenic silica)
- Physical state: solid
- Composition of test material, percentage of components: Zeosil 45 - SiO2 >97.3%; Syloid 74 - SiO2 >99.5%; Cab-O-Sil - SiO2 >99.7%
- Other: all three synthetic amorphous silicas are spherical and hydrophilic

Test animals

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:

Administration / exposure

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

Doses / concentrations

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)

Examinations

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.

Results and discussion

Results of examinations

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

Effect levels

Dose descriptor:

NOAEL

Effect level:

1 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: synthetic amorphous silica

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

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.

Applicant's summary and conclusion

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.