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Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Publication of a GLP guideline study reliable with restrictions Deviations from the guideline OECD 413 (1981): - no explicit statement is made in the publication if the actual concentration of the test substance was held as constant as practicable. No raw data of the actual concentration was presented, no indication was made if exposure started after a test atmosphere equilibration period. However, supporting publications by Jung, 2006 and Ji, 2007 specifically address and confirm the generation of a stable test atmosphere for this study in the same laboratory. - the temperature and humidity values are reported for the acclimatisation period only, but not explicitly for the test period - there was no indication that the animals were observed during the 6-hour exposure period. - animals were not observed every day, but on weekdays only - apparently, the animals were ophthalmologically examined, but it was not described when the examination took place and if all animals were examined. It seemed that at least the high dose group was examined, since it was stated that one animal from the high dose died during this examination, but no further information could be found regarding this examination. - it was not explicitly mentioned, if a full gross necropsy was performed. - baseline data was not given for haematological and biochemistry tests
Cross-reference
Reason / purpose:
reference to same study

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Unnamed
Year:
2009
Report Date:
2008
Reference Type:
publication
Title:
Long-term Stability Characterisitics of Metal Nanoparticle Generator Using Small Ceramic Heater for Inhalation Toxicity Studies
Author:
Ji, J.H. et al.
Year:
2007
Bibliographic source:
Inhalation Toxicology 19: 745-751
Report Date:
2007
Reference Type:
publication
Title:
Metal nanoparticle generation using a small ceramic heater with a local heating area
Author:
Jung, J. H. et al.
Year:
2006
Bibliographic source:
Aerosol Science 37: 1662 - 1670
Report Date:
2006
Reference Type:
other company data
Title:
Unnamed
Year:
2012
Report Date:
2012

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
Version / remarks:
, adopted 1981-05-12
Deviations:
yes
Remarks:
, please refer to "Rationale for reliability incl. deficiencies" above
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: nanomaterial, average particle size 18-20 nm
Details on test material:
- Name of test material (as cited in study report): silver nanoparticles
- silver nanoparticles were generated by a ceramic heater (see also references Ji, 2007 and Jung, 2006)
- electron microscopy showed that all particles were smaller than 55nm and the diameters were lognormally distributed between 6 and 55 nm.
- count median particle diameter 18 nm (geometric standard deviation = 1.5)
- x-ray diffraction analysis of the particles surface showed that the particles were not oxidised

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS - specific-pathogen-free
- Source: SLC (Tokyo, Japan)(originally derived from the Charles River SD in 1968)
- Age at study initiation: 8 week-old rats
- Weight at study initiation: males: approximately 253 g; females: approximately 162 g
- Fasting period before study: not stated
- Animals were not provided with food during the 6-hour exposure period.
- Housing: during the acclimation and experimental periods, the rats were housed in polycarbonate cages (five rats per cage).
- The animals were housed in individual wire cages during the exposure period.
- Diet (ad libitum, except during exposure): a rodent diet (Harlan Teklab, Plaster International Co., Seoul, South Korea)
- Water (ad libitum): filtered water
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 23 ± 2°C
- Humidity: 55 ± 7%
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
inhalation: aerosol
Type of inhalation exposure:
whole body
Vehicle:
clean air
Remarks on MMAD:
MMAD / GSD: no data, please refer to "Any other information on materials and methods incl. tables" below.
Details on inhalation exposure:
Silver nanoparticles were generated as described in previous reports (Ji et al., 2007a,b; Jung et al., 2006)*.

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: the rats were exposed to the silver nanoparticles in a whole-body-type exposure chamber (1.3 m^3, Dusturbo, Seoul, South Korea).

- System of generating particulates/aerosols: the generation consisted of a small ceramic heater connected to an alternating current power supply and housed within a quartz tube case. The heater dimensions were 50 X 5 X 1.5 mm^3, and a surface temperature of about 1500°C within local heating area of 5 X 10 mm^2 could be achieved within about 10 s. For long-term testing, the source material (about 160 mg) was positioned at the highest temperature point. The quartz tube case was 70 mm in diameter and 140 mm long. Clean (dry and filtered) air was used as the carrier gas, and the gas flow maintained at 30.0 L/min (Re = 572, laminar flow regime) using a mass flow controller (MFC, AERA, FC-7810CD-4V, Japan). This generator has been shown to generate nanoparticles from 2 to 65 nm in diameter which do not agglomerate in air. X-ray diffraction analysis using an X-ray diffractometer utilizing CuK2 radiation showed that particles generated are metallic silver, not silver oxide.
The system produced different concentrations of nanoparticles (high, middle, and low) in three separate chambers. For the high-concentration chamber, the nanoparticle generator was operated at 47 L/min and mixed with 200 L/min of clean ambient air. A portion of the high nanoparticle concentration was then diverted to the middle-concentration chamber using the MFC for the first dilution (6.76 ± 0.16 liter per minute (Lpm), mean ± SE), and a portion of the middle nanoparticle concentration then diverted to the low-concentration chamber using the second MFC (5.42 ± 0.18 Lpm).

- Method of particle size/particle concentration determination: the nanoparticle distribution with respect to size was measured directly in real-time using a differential mobility analysing system (DMAS); combining a differential mobility analyser (Short type-DMA, 4220, HCT Co., Ltd, Korea; range 5 - 150 nm) and condensation particle counter (CPC, 4312, HCT Co., Ltd, 0 - 10^8/cm^3 detection range). Nanoparticles were measured using sheath air at 5 L/min and polydispersed aerosol air at 1 L/min for DMA and CPC, respectively. The particle concentration in the fresh-air control chamber was measured using a particle sensor (4123, HCT Co., Ltd) that consisted of two channel; 300 - 1000 nm and over 1000 nm.
The filters used to sample the fume particles were coated with carbon, mounted on an electron microscope grid (200 mesh, Veco, Eerbeek, the Netherlands), and visualized under a transmission electron microscope (TEM, Hitachi 7100, Japan). The diameters of 800 randomly selected particles were measured at a magnification of 100,000, and the silver particles analysed using an energy-dispersive x-ray analyzer (EDX-200, Horiba, Japan) at an accelerating voltage of 75 kV.

* References:
Ji, J.H., Jung, J. H., Yu, I. J., and Kim, S.S. (2007a). Long-term stability characteristics of metal nanoparticle generator using small ceramic heater for inhalation toxicity studies. Inhal. Toxicol. 19, 745 - 51.
Ji, J. H., Jung, J. H., Kim, S. S., Yoon, J. U., Park, J. D., Choi, B. S., Chung, Y. H., Kwon, I. H., Jeong, J., Han, B.S., et al. (2007b). Twenty-eight days inhalation toxicity study of silver nanoparticles in Sprague-Dawley Rats. Inhal. Toxicol. 19, 857 - 871.
Jung, H. H., Oh, H. C., Noh, H.S., Ji, J.H., and Kim, S.S. (2006). Metal nanoparticle generation using a small-sized ceramic heater with a local heating area. J. Aerosol Sci. 37, 1662 - 1670.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Please refer to "Details on inhalation exposure" above.
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
6 hours/day, 5 days/week
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0 µg/m^3
Basis:
other: control
Remarks:
Doses / Concentrations:
49 µg/m^3
Basis:
analytical conc.
Remarks:
Doses / Concentrations:
133 µg/m^3
Basis:
analytical conc.
Remarks:
Doses / Concentrations:
515 µg/m^3
Basis:
analytical conc.
No. of animals per sex per dose:
10 males/10 females
Control animals:
yes, sham-exposed
Details on study design:
- Dose selection rationale: as there is no current data on workplace air concentrations of silver nanoparticles or silver nanoparticle concentrations released from consumer products, the concentrations used in this study are difficult to relate human exposures. Concentrations used in this study were based on the current ACGIH silver dust threshold limit value (TLV) of 0.1 mg/m3 (ACGIH, 2001)*. As such, the low, middle, and high doses were 1/2, 1, and 5 times the ACGIH silver dust TLV, respectively, in terms of mass dose. In addition, the high dose used in this study is nearly 500-fold higher than the ACGIH silver dust TLV in terms of surface area.

Reference:
American Conference of Governmental Industrial Hygienists (ACGIH). (2001). Documentation of the TLVs and BEIs. ACGIH, Cincinnati, OH.
Positive control:
not used

Examinations

Observations and examinations performed and frequency:
ANIMAL OBSERVATIONS: Yes
- Time schedule: daily on weekdays
- Observations checked: any evidence of exposure-related effects, including respiratory, dermal, behavioural, nasal, or genitourinary changes suggestive of irritation.

BODY WEIGHT: Yes
- Time schedule for examinations: at purchase, at the time of grouping, once a week during the inhalation exposure and before necropsy.

FOOD CONSUMPTION: Yes
- Time schedule: weekly

FOOD EFFICIENCY: No data

WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: no data
- Dose groups that were examined: not explicitly stated, but it is assumed that all groups were checked

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at the end of the 13-week experiment (before necropsy); blood was drawn from the abdominal aorta and collected in heparinized vacutainers.
- Anaesthetic used for blood collection: Yes; anesthetized with pentobarbital
- Animals fasted: Yes, food was withheld for 24 hours
- How many animals: all
- Parameters checked: white blood cell count, red blood cell count, haemoglobin concentration, haematocrit, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, red-cell distribution width, platelet count, mean platelet volume, number of neutrophils, percent of neutrophils, number of lymphocytes, percent of lymphocytes, number of monocytes, percent of monocytes, number of eosinophils, percent of eosinophils, number of basophils, and percent of basophils

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at the end of the 13-week experiment (before necropsy); blood was drawn from the abdominal aorta and collected in heparinized vacutainers.
- Anaesthetic used for blood collection: Yes; anesthetized with pentobarbital
- Animals fasted: Yes, food was withheld for 24 hours
- How many animals: all
- Parameters checked: albumin, alkaline phosphatase, calcium, cholesterol, creatinine, gamma-glutamyl transpeptidase, glucose, glutamic oxalacetic transaminase, glutamic pyruvic transaminase, inorganic phosphorus, lactate dehydrogenase, magnesium, total protein, uric acid, blood urea nitrogen, total bilirubin, creatine phosphokinase, sodium, potassium, chloride, triglyceride, and ratio albumin to globulin

URINALYSIS: No data

NEUROBEHAVIOURAL EXAMINATION: No data
Sacrifice and pathology:
ORGAN WEIGHTS AND HISTOPATHOLOGY:
After collecting the blood, the rats were sacrificed by cervical dislocation, and the adrenal glands, bladder, testes, ovaries, uterus, epididymis, seminal vesicle, heart, thymus, thyroid gland, trachea, oesophagus, tongue, prostate, lungs, nasal cavity, kidneys, spleen, liver, pancreas, and brain all removed carefully. Organs were weighed and fixed in a 10% formalin solution containing neutral phosphate-buffered saline. The organs were embedded in paraffin, stained with hematoxylin and eosin. All organs from all animals were examined under light microscopy.

Other examinations:
DETERMINATION OF TISSUE SILVER:
After wet digestion using a flameless method, the tissue concentrations of silver were analysed using an atomic absorption spectrophotometer equipped with a Zeeman graphite furnace (Perkin Elmer 5100ZL, Zeeman Furnace Module, Waltham, MA) based on the NIOSH 7300 method (NIOSH (1999), NIOSH Manual of Analytical Methods. Method No. 7300, 7604. National Institute for Occupational Safety and Health, Cincinnati, OH).
Statistics:
All the results were expressed as the means ± SE. An ANOVA test and Duncan's multiple range tests were used to compare the body weights, bronchoalveolar lavage cell distributions, and parameters from the lung function test obtained for the three dose groups with those obtained for the control rats. Histopathological results were analysed by Chi-squared analysis. Level of significance was set at p < 0.05 and p < 0.01.

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 specified
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:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
not specified
Details on results:
CLINICAL SIGNS AND MORTALITY
No gross effects were observed during the 90-day exposure period. One animal from the high-dose group died during the opthalmological examination.

BODY WEIGHT AND WEIGHT GAIN
There were no significant changes in body weights of male rats. Although female rats showed a significant body weight difference between high and middle dose groups, there were no significant dose-related changes.

FOOD CONSUMPTION
No significant differences were observed in food consumption between the exposed rats and the control groups.

HAEMATOLOGY
There were no significant dose-related differences in the haematology values among groups.
To evaluate aggregation of red blood cells or blood coagulation attributable to silver nanoparticles, erythrocyte aggregation, activated partial thromboplastin time, and prothrombin time were tested. Only the percent of aggregation in the high-dose females showed a statistically significant difference compared with the controls.

CLINICAL CHEMISTRY
There were no significant dose-related differences in the blood biochemical parameters.

ORGAN WEIGHTS
No significant organ weight changes were observed in either the male or female rats after the 90 days of silver nanoparticle exposure.

HISTOPATHOLOGY: NON-NEOPLASTIC
Liver:
- minimal bile-duct hyperplasia was identified in 0/10, 0/10, 1/10, and 4/9 of the control, low, middle, and high dose males, respectively.
- one high-dose male had minimal bile-duct hyperplasia with minimal portal mineralization.
- the higher incidence of bile-duct hyperplasia in the high dose males, with or without mineralization suggested a minimal test article-related effect.
- minimal bile-duct hyperplasia was present in 3/10, 2/10, 4/10, and 8/10 of the control, low, middle, and high dose females, respectively.
- single-cell hepatocellular necrosis, characterised by increased cellular eosinophilia and shrunken condensed nucleo, was noted in 3/10 high dose females.
- one high dose female exhibited moderate bile-duct hyperplasia with concurrent moderate centrilobular fibrosis, minimal single-cell hepatocyte necrosis, mild pigment accumulation, and moderate multifocal necrosis.
- the higher incidence of bile-duct hyperplasia, with or without necrosis, fibrosis, and/or pigmentation, in high dose females suggested a test-article-related effecte, which was slightly mor obvious than in the males.
Please also refer to "Any other information on results incl. tables" below (Table 1 and 2).

Lung:
- examination revealed a high incidence of minimal alterations, including some chronic alveolar inflammation, a mixed cell perivascular infiltrate, and alveolar macrophage accumulation in high dose male and female animals when compared with the controls.
Please also refer to "Any other information on results incl. tables" below (Table 1 and 2).

Nasal pathways:
- no histopathologic findings in the nasal pathways were considered test article related.

Kidneys:
- incidence of minimal tubular basophilia was noted in all the groups, including the controls, and thus not considered to be test article exposure related.
- tubular basophilia was more prevalent in males compared with the females.
- although tubular dilatation, cast formation, mineralization, and inflammation were noted occasionally in the control and/or treated animals, they were considered to be within the range of expected background spontaneous change.

Heart:
- minimal degeneration/necrosis was observed in all the groups, including the controls, indicating that this alteration was not test article related.
- the change was more obvious in the males.
- the finding is a common spontaneous background change.

Harderian gland/prostate
- inflammation was noted occasionally, which is a common background spontaneous finding and thus not considered to be test article related.

OTHER FINDINGS
Silver distribution in tissue:
- silver concentration in lung tissue from groups exposed were statistically significant (p < 0.01) and increased with dose.
- a clear dose -dependent increase in silver concentration in the blood for both genders.
- dose-dependent increase in the liver silver concentration for both genders.
- silver concentration in the olfactory bulb was higher than in brain, and increased in a dose dependent manner in both the male and female rats (p<0.01).
- silver concentration in the kidneys showed a gender difference with the female kidneys containing two to three times more silver acculmulation than in male kidneys.
- because gender difference in silver accumulation was noted in kidneys, the kidney function was measured based on the N-acetylglutamate and protein in urine. No significant difference was noted among the dose groups and between genders, except for an increase of protein in the urine from the high-dose male rats (high-dose group: 2.57± 0.13 g/g creatinine; control group: 1.89 ± 0.11 g/g creatinine; p < 0.05).
Please also refer to "Any other information on results incl. tables" below (Table 3 and 4).

Effect levels

open allclose all
Dose descriptor:
NOAEC
Effect level:
133 other: µg/m^3
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: see 'Remark'
Dose descriptor:
LOAEC
Effect level:
515 other: µg/m^3
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: see 'Remark'

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables

Histopathology

Table 1: Histopathological findings for male rats

Group

Control

Low

Middle

High

Number of animals

10

10

10

9

 

N

%

N

%

N

%

N

%

Liver

No microscopic findings

 

 

10/10

100

10/10

100

9/10

90

5/9

55.6

 

Abnormality*

 

 

0/10

0

0/10

0

1/10

10

4/9

44.4

 

Necrosis

Multifocal

Minimum

0/10

0

0/10

0

0/10

0

1/9

11.1

 

Hyperplasia*

Bile duct

Minimum

0/10

0

0/10

0

1/10

10

4/9

44.4

 

Vacuolation

Hepatocellular

Minimum

0/10

0

0/10

0

0/10

0

1/9

11.1

 

Mineralization

Portal

Minimum

0/10

0

0/10

0

0/10

0

1/9

11.1

Lungs

No microscopic findings

 

 

5/10

50

3/10

30

3/10

30

0/9

0

 

Abnormality

 

 

5/10

50

7/10

70

7/10

70

9/9

100

 

Accumulation

Macrophage, alveolar

Minimum

3/10

30

5/10

50

5/10

50

8/9

88.9

 

Inflammation**

Chronic, alveolar

Minimum

2/10

20

3/10

30

2/10

20

8/9

88.9

 

Infiltrate

Mixed cell perivascular

Minimum

3/10

30

4/10

40

6/10

60

7/9

77.8

 

Hemorrhage

Alveolar

Minimum

1/10

10

0/10

0

0/10

0

0/9

0

 

Osseous foreign body

 

 

0/10

0

0/10

0

0/10

0

1/9

11.1

 

Hyperplasia

Respiratory epithelium

level I

 

0/10

0

0/10

0

0/10

0

1/9

11.1

* p < 0.05, compared with control, ** p < 0.01, compared with control

Table 2: Histopathological findings for female rats

Group

Control

Low

Middle

High

Number of animals

10

10

10

10

 

N

%

N

%

N

%

N

%

Liver

No microscopic findings

 

 

7/10

70

5/10

50

5/10

50

1/10

10

 

Abnormality*

 

 

3/10

30

5/10

50

5/10

50

9/10

90

 

Necrosis

Multifocal

Minimum

2/10

20

0/10

0

0/10

0

0/10

0

 

 

 

Moderate

0/10

0

0/10

0

0/10

0

1/10

10

 

 

Focal

Minimum

0/10

0

0/10

0

1/10

10

0/10

0

 

 

Single-cell hepatocellular *

Minimum

0/10

0

0/10

0

0/10

0

3/10

30

 

Hyperplasia*

Bile duct

Minimum

3/10

30

2/10

20

4/10

40

8/10

80

 

 

 

Moderate

0/10

0

0/10

0

0/10

0

1/10

10

 

Granuloma

Multifocal

Minimum

0/10

0

2/10

20

0/10

0

0/10

0

 

Vacuolation

Hepatocellular

Minimum

0/10

0

1/10

10

0/10

0

0/10

0

 

Fibrosis

Centrilobular

Mild

0/10

0

0/10

0

0/10

0

1/10

10

 

Pigment

Centrilobular

Mild

0/10

0

0/10

0

0/10

0

1/10

10

Lungs

No microscopic findings

 

 

3/10

30

5/10

50

6/10

60

2/10

20

 

Abnormality

 

 

7/10

70

5/10

50

4/10

40

8/10

80

 

Accumulation

Macrophage, alveolar

Minimum

7/10

70

4/10

40

4/10

40

6/10

60

 

Inflammation**

Chronic, alveolar

Minimum

3/10

30

2/10

20

0/10

0

8/10

80

 

Infiltrate**

Mixed cell perivascular

Minimum

0/10

0

0/10

0

1/10

10

7/10

70

* p < 0.05, compared with control, ** p < 0.01, compared with control

Silver distribution in tissue

Table 3: Tissue content of silver in male rats (mean± SE) (Unit: ng/g tissue wet weight)

 

Control

Low

Middle

High

Liver

0.70 ± 0.20 (3)

3.52 ± 0.98 (5)

13.75 ± 2.28 (5)

132.97 ± 22.87* (4)

Kidneys

0.85 ± 0.20 (5)

1.63 ± 0.33 (5)

3.58 ± 0.41** (5)

9.49 ± 0.86* (4)

Olfactory bulb

0.51 ± 0.38 (3)

6.44 ± 0.77 (5)

17.10 ± 1.61 (5)

30.48 ± 2.15*** (4)

Brain

1.12 ± 0.34 (2)

3.45 ± 0.73 (4)

7.89 ± 0.95** (5)

18.63 ± 1.24* (4)

Lungs

0.77 ± 0.25 (5)

613.57 ± 66.03† (5)

5450.29 ± 904.17** (5)

14645.42 ± 2630.24* (4)

Whole blood

0.09 ± 0.02 (7)

0.68 ± 0.08 (10)

1.82 ± 0.20** (10)

4.31 ± 0.37* (9)

Note. (): number of samples.

*p < 0.01, high-dose versus other groups.

** p < 0.01, middle-dose versus unexposed and low-dose groups.

*** p < 0.01, high-dose versus other groups (dose dependent).

†p < 0.05, male versus female in low-dose group.

Table 4: Tissue content of silver in female rats (mean± SE) (Unit: ng/g tissue wet weight)

 

Control

Low

Middle

High

Liver

0.90±0.31 (5)

4.55±1.40 (5)

12.07±2.50 (5)

71.08±24.50* (5)

Kidneys

0.94±0.18 (4)

2.61±0.57 (5)

11.81±4.27 (4)

37.66±7.04*(5)

Olfactory bulb

2.26±0.74 (4)

7.43±0.75 (5)

13.75±1.32 (5)

32.84±2.74*** (5)

Brain

0.66±0.26 (4)

4.09±0.46 (5)

10.22±1.19** (5)

19.97±2.41* (5)

Lungs

1.01±0.10 (3)

295.92±78.50 (5)

4241.17±641.10** (5)

20585.63±1880.31* (5)

Whole blood

0.05±0.01 (5)

0.85±0.14 (10)

2.10±0.22** (10)

6.86±0.60*,(10)

Note. (): number of samples.

*p < 0.01, high-dose versus other groups.

** p < 0.01, middle-dose versus unexposed and low-dose groups.

*** p < 0.01, high-dose versus other groups (dose dependent).

†p < 0.05, female versus male in low-dose group.

p < 0.01, female versus male in high-dose group.

Applicant's summary and conclusion

Conclusions:
The results of this subchronic 90-day silver nanoparticle inhalation toxicity indicated that lungs and liver were the major target tissues for prolonged silver nanoparticle accumulation.
The NOAEC of 133 µg/m^3 is based on test article-related effects seen at higher (515 µg/m^3) exposure concentrations (minimal bile-duct hyperplasia in males and females, chronic alveolar inflammation and macrophage accumulation in the lungs of males and females, and erythrocyte aggregation in females) of nano-silver (test atmosphere characterised by a count median diameter of 18 nm).
This rat NOAEC was corrected to human equivalent concentrations (HEC) for typical, commercial non-nano silver metal powders (D50 in µm range) based on particle size considerations and modelled comparative fractional deposition in the respiratory tract (rats/humans). The resulting HECs under various considerations are all >> 3 mg/m³ (EBRC, 2012). In contrast, the current OEL set by SCOEL based on human data and taken forward as the DNEL is 0.1 mg/m^3. Since this is more than one order of magnitude lower than the HEC based on animal data with nano-silver, the more conservative approach based on human data as derived by SCOEL was adopted as the DNEL.