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Toxicological information

Acute Toxicity: inhalation

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Administrative data

Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Publication, based on results form a OECD (403, 1995) study in accordance with GLP. Relevant experimental details and results are reported.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2011

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
Version / remarks:
adopted 1981-05-12
Deviations:
no
GLP compliance:
yes
Test type:
standard acute method
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

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS - Specific-pathogen free Sprague Dawley rats (Slc:SD; originally derived from the Charles River SD in 1968)
- Source: Orient Bio (Seongnam, Korea)
- Age at study initiation: 7 weeks
- Weight at study initiation: approximately 218 g (males) and 153 g (females)
- Housing: during the acclimation and experimental periods, the rats were housed in five mesh cages (five rats per cage) in a room with controlled temperature and humidity. During the exposure period, the animals were housed in individual wire cages.
- Diet (ad libitum): a rodent diet (Harlan Teklab, Plaster International Co., Seoul
- Water (ad libitum): filtered water
- Acclimation period: 1 week before starting the experiments

ENVIRONMENTAL CONDITIONS
- Temperature: 23°C ± 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
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus and exposure chamber volume: a whole-body-type exposure chamber (1.3 m^3, Dusturbo, Seoul)

- System of generating particulates/aerosols: the silver nanoparticles were generated as described in previous reports (Ji et al., 2007a; 2007b; Jung et al., 2006; Sung et al., 2009)*. The generation consisted of a small ceramic heater connected to an AC power supply (AC 95 V) 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 a local heating area of 5 X 10 mm^2 was achieved within about 10 sec (Jung et al., 2006)*. The source material (about 160 mg, Daedeok Science, Daejeon) 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 54.0 L/min (Re 1/4 572, laminar flow regime) using a mass flow controller (MFC, AERA, FC7810CD-4V, Japan; Ji et al., 2007a,b)*. This generator has already been shown to generate nanoparticles from 5 to 95 nm in diameter that do not agglomerate in air. Plus, an X-ray diffraction analysis using an X-ray diffractometer utilising CuK2 radiation showed that the particles generated are metallic silver, not silver oxides (Jung et al., 2006)*. In the current study, the system produced different concentrations of nanoparticles (high, middle, and low) in three separate chambers.

- Method of particle size and test atmosphere determination: in each chamber, 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 2 - 150 nm) and condensation particle counter (CPC, 4312, HCT Co., Ltd, Korea, 0 - 10^8/cm^3 detection range). The nanoparticles were measured using sheath air at 5 L/min and polydispersed aerosol air at 1 L/min for the DMA and CPC, respectively. The particle concentration in the fresh-air control chamber was measured using a particle sensor (4123, HCT Co., Ltd, Korea) that consisted of two channels; 300 - 1000 nm and over 1000 nm.

TEST ATMOSPHERE (if not tabulated)
(Please also refer to Table 1 in the field "Any other information on materials and methods incl. tables" below)

*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. Inhalation Toxicology 19(9): 745 - 751.
- Ji, J.H., Jung, J.H., Kim, S.S., Yoon, J.U., Park, J.D., Choi, B.S., et al. (2007b) A twenty eight-days inhalation toxicity study of silver nanoparticles in Sprague-Dawley rats. inhalation Toxicology 19(10): 857 - 871.
- Jung, J.H., Oh, H.C., Noh, H.S., Ji, J.H., and Kim, S.S. (2006) metal nanoparticle generation usng a small-sized ceramic heater with a local heating area. Journal of Aerosol Science 37: 1662 - 1670.
- Sung, J.H., Ji, J.H., PArk, J.D., Yoon, J.U., Kim, D.S., Jeon, K.S. et al. (2009) Subchronic inhalation toxicity of silver nanoparticles. Toxicological Science 108(2): 452 - 461.
Analytical verification of test atmosphere concentrations:
yes
Remarks:
please refer to "Details on inhalation exposure" above.
Duration of exposure:
4 h
Concentrations:
Actual concentrations:
- low-dose group: 75.84 +/- 3.25 µg/m^3
- middle-dose group: 134.62 +/- 5.99 µg/m^3
- high-dose group: 750.00 +/- 35.62 µg/m^3

Note by the authors: "While more than 3 10^6 particles/cm3 (ca. 730 µg/m^3) could be achievable, this would generate a lot of sub-micron-sized agglomerated/ aggregated particles, which are less than desirable conditions for studying the effects of nanosized particles.

(Please also refer to Table 1 in the field "Any other information on materials and methods incl. tables" below)
No. of animals per sex per dose:
5 males / 5 females
Control animals:
yes
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: daily on weekdays for any evidence of exposure-related effects including: respiratory, dermal, behavioural, nasal, or genitourinary changes suggestive of irritation.
- Body weights: at purchase, at the time of grouping, and 1, 3, 7, and 14 days after the 4-hour inhalation exposure and before necropsy.
- Other examinations performed: Lung function tests were conducted on four rats from each dose group. The lung function of the exposed rats was evaluated at purchase and 1, 3, 7, and 14 days after the 4-hour inhalation exposure using a ventilated bias flow whole-body plethysmograph (WBP; SFT3816, Buxco Electronics, Sharon, Connecticut, USA), consisting of a reference chamber and animal chamber interconnected by a pressure transducer (MAX1320, Buxco Electronics). The parameters for the pulmonary function test included the tidal volume (TV, mL), minute volume (MV, mL/min), respiratory frequency (BPM, breath/min), inspiration time (Ti, sec), expiration time (Te, sec), peak inspiration flow (PIF, mL/sec), and peak expiration flow (PEF, mL/s). After being exposed to the silver nanoparticles for 4 hours, the rats were placed in the animal chamber, left for 40 min to stabilize, and the plethysmography initiated by measuring the selected parameter values for 5 min (Sung et al., 2008)*.

* Reference:
- Sung JH, Ji JH, Yun JU, Kim DS, Song MY, Jeong J, et al. (2008) Lung function changes in Sprague-Dawley rats after prolonged inhalation exposure to silver nanoparticles. Inhalation Toxicology 20(6): 567–574.
Statistics:
All the results are expressed as the means ± standard error (SE). An analysis of variance (ANOVA) test and Duncan’s multiple range tests were used to compare the body weights and parameters from the lung function test obtained for the three dose groups with those obtained for the control rats.
The level of significance was set at p < 0.05 and p < 0.01.

Results and discussion

Effect levels
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 750 other: µg/m^3
Based on:
test mat.
Exp. duration:
4 h
Remarks on result:
other: 750 µg/m³ was the maximum attainable concentration that was possible without masking the effects assessment of nano-particles by generation of non-nano-sized agglomerates.
Mortality:
No mortality was observed related to the test substance.
Clinical signs:
other: No toxic signs were observed related to the test substance.
Body weight:
There were no significant changes in the body weights of the male and female rats.
Gross pathology:
No significant gross effects were observed.
Other findings:
- Food consumption: no significant differences were observed in food consumption between the exposed rats and the control group.
- Lung function test: although some statistically significant differences were found in the lung function parameters, such as the tidal volume and minute volume, among the dose groups, no significant dose-dependent changes were found in the lung function parameters for the male and female rats exposed to the silver nanoparticles

Applicant's summary and conclusion

Interpretation of results:
not classified
Remarks:
Migrated information Criteria used for interpretation of results: EU
Conclusions:
LC50 (male and female rats; 4 h) > 750 µg/m^3 ( or 3.1 x 10^6 particles/cm^3)
The following statement was given by the authors of the publication:
"While more than 3 x 10^6 particles/cm^3 could be achievable, this would generate a lot of sub-micron-sized agglomerated/aggregated particles, which are less than desirable conditions for studying the effects of nanosized particles. Plus, exposure to more than a million silver nanoparticles/cm^3 is unlikely in a living environment or from silver nanoparticle-containing consumer products. Thus, the highest concentration in the current exposure assessment study would not be aniticpated in a real silver nanoparticle manufacturing workplace (mansucript in submission)."