Inhalation Experiments with Coal Dust Containing 5 Per Cent, 10 Per Cent, 20 Per Cent and 40 Per Cent Quartz: Tissue Reactions in the Lungs of Rats

Abstract

Rats were exposed for 16 hr per day to mixed clouds of coal (anthracite) and quartz dust ranging from 5–40 per cent of quartz. The dust exposures lasted for 10–17 months at concentrations of the order of 60 mg/m 3 of respirable dust or 25,000 p.p.cm 3 . Some animals were allowed to survive one and three months after the end of dusting. Histological observations were made on all lungs and dust and collagen analyses on some of them. Rats exposed to mixtures of coal with 5 and 10 per cent of quartz showed evidence of dust uptake but little fibrosis of the lungs. The fibrosis did not reach Grade 2 after 500 days of dusting. However, in the 10 per cent quartz series, Grade 2 fibrosis was found in the lymph glands. The highest grade of fibrosis reached with 20 per cent quartz was Grade 2, and with 40 per cent quartz it was Grade 4. Rats exposed to 20 and 40 per cent quartz-coal mixtures had after ten months, the end of the dust exposure, accumulated on average 106 mg of dust. The quartz percentage of the lung dust was similar to that of the airborne dust. One hundred days later there was slightly less dust in the lungs, but there was no evidence of differential removal of coal or quartz. Collagen analyses were in reasonable agreement with the histological observations. It is concluded that injection experiments are more sensitive than inhalation experiments to show up the effects of small proportions of quartz in coal-quartz mixtures.