Injected ground crocidolite causing hair depigmentation

Depigmentation of hair in mice has been produced by many carcinogens and tumour promoters. Complete carcinogens would possess both initiating and promoting activity. Depigmentation occurred with fine suspensions of crocidolite but not with coarse suspensions of crocidolite or other forms of asbestos. Crocidolite exposure presents a greater carcinogenic risk than other forms of asbestos and this is probably due to its effectiveness as a tumor-promoter. The physical characteristics of asbestos fibres may be important with regard to its carcinogenicity. Fine grinding of the crocidolite fibres alters the physical configuration and this may increase its tumour-promoting properties hence producing the depigmentation effect not seen with unground crocidolite. No tumours were seen in the mice injected with asbestos even when there was pretreatment with urethane. This may be due to an inadequate dose of urethane and/or asbestos.