Clearance of deposited silicon carbide whisker from rat lungs inhaled during a 4-week exposure.
Pulmonary deposition and the clearance of deposited fiber particles from lungs are key determinant factors in assessing potential carcinogenicity and fibrogenicity. Forty-two Wistar male rats (9 wk old) were exposed to silicon carbide whisker (SiCW) for 6 h/d, 5 d/wk for 4 wk. The mass median aerodynamic diameter was 2.5 microm as detected by an Andersen sampler, and the geometric mean fiber diameter and length determined by a scanning electron microscope were 0.4 and 2.2 microm, respectively. The daily average exposure concentrations were 10.4 0.5 mg/m(3) (214 +/- 31 fibers/ml ) during the exposure period. The rats were sacrificed after 3 d, 2 wk, 1, 2, 3, 6 and 12 months after 4-wk exposure. At the time of sacrifice, the wet lung weights and the deposited SiCW amounts in the lungs were measured by an X ray reference method. The amount of SiCW deposited was 0.60 +/- 0.09 mg 3 d after a 4-wk exposure. The apparent deposition fraction was 4.8 +/- 0.7 (%). During the clearance period, the amount of SiCW deposited in the rat lungs decreased exponentially with the increasing duration of the clearance period. The biological half time in the one-compartment model was determined to be 4.0 months which is similar to the values for glass fiber, potassium titanate whisker and aluminium-silicate ceramic fiber under similar exposure conditions.
Akiyama
Izumi
I
Department of Environmental Health Engineering, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Japan.
Ogami
Akira
A
Oyabu
Takako
T
Yamato
Hiroshi
H
Morimoto
Yasuo
Y
Tanaka
Isamu
I
D000280:Administration, Inhalation; D000818:Animals; D017554:Carbon Compounds, Inorganic / Q000633:toxicity*; D008168:Lung / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D010316:Particle Size; D051381:Rats; D017208:Rats, Wistar; D017655:Silicon Compounds / Q000633:toxicity*
D017554:Carbon Compounds, Inorganic; D017655:Silicon Compounds; C022088:silicon carbide