The mouse-skin carcinogenicity of a mutagenic fraction from beech wood dusts

A life-time mouse-skin carcinogenicity assay was conducted using female NMRI mice to evaluate the possible direct carcinogenic activity of a mutagenic fraction isolated from beech wood dusts. The samples of untreated beech wood dusts were extracted with methanol at pH3 and were purified from the inhibitory compounds toxic to bacteria, using silica-gel column chromatography. The fraction obtained after passing through the column was tested for mutagenicity in the Ames assay employing Salmonella typhimurium TA100 in the presence of Aroclor-treated rat-liver-S9. Using acetone as the vehicle, this mutagenic fraction was tested for carcinogenicity on an area of 1-1.5 cm shaved skin of mice on the lower back. The mice were treated with half of each dose, twice a week, for only 3 months. The total doses applied per week were 2.5, 5, 7.5 or 10 g equivalent dust/mouse. No substance was used as promoter. No statistically significant difference was found when the life spans of treated and untreated animals were compared. The observed carcinogenic effect was based on tumours and lesions found only on the site of application of the test material. Of 210 mice (effective number, 129) serving as the negative controls, three developed skin lesions but no tumours. Of 280 treated animals (effective number, 188) 34 developed different types of tumours and 20 had a uniform type of precancerous skin lesion. Of 34 tumours observed 21 were originated from the skin, 12 from the mammary glands beneath the site of application, and one was a lymphoma. Comparing the negative controls with the treated animals, the overall carcinogenic effect observed was dose-dependent and statistically significant. Excluding the mammary tumours and a lymphoma found beneath the site of treatment, the overall induction of skin tumours was still significant. However, the dose-dependent increase in the number of skin tumours alone was not statistically significant. These results suggest that beech wood dust contains mutagenic and carcinogenic constituent(s).