Mouse skin tumorigenicity studies of indoor coal and wood combustion emissions from homes of residents in Xuan Wei, China with high lung cancer mortality

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Abstract
The rural Xuan Wei County, Yunnan Province, China, has an unusually high lung cancer mortality rate that cannot be attributed to tobacco smoke or occupational exposure. The lung cancer rate is associated with ‘smoky’ coal, in contrast to wood or ‘smokeless’ coal burned in unventilated homes. This study was conducted to characterize and compare mouse skin tumorigenicity of the coal and the wood combustion emissions and to link the animal data to human lung cancer. Indoor air particles (<10 μm) were collected from a central commune where the lung cancer mortality rate is high and smoky coal is the major fuel used and also from a south western commune where lung cancer mortality rate is low and where wood or smokeless coal are the major fuels used. The organic extracts of these indoor air particles from smoky coal, smokeless coal and wood combustion were analysed for polycyclic aromatic hydrocarbons and assayed for skin tumor initiation activity and complete carcinogenicity in SENCAR mice. The results showed that the organic extract of the emission particles from smoky coal combustion is the most active in tumor initiation among the three combustion emission samples followed by smokeless coal and then wood. The organic extract of the particles from smoky coal combustion was shown to be a potent complete carcinogen, whereas the wood extract was relatively inactive as a complete carcinogen. The extract of particles from the smokeless coal combustion was not tested for complete carcinogenicity because of inadequate supply. Eighty-eight percent of the mice treated with the smoky coal extract showed carcinomas, averaging 1.1 carcinomas per tumor-bearing mouse at the end of the 77 week study. These findings were in agreement with the epidemiological data, which showed that the Xuan Wei residents using smoky coal as a major fuel in homes had a high lung cancer mortality rate. This study demonstrates that the results of the tumorigenicity assays in mice were in agreement with human lung cancer data.