Document K6XvONjX8XK1MVvVpQY8YkGEx

REl n survival -e '""8 e were 17 . 118 ,nly 6 of tiung 'bestosis (250/ * ,nce ^<o.0o,J: lung "'f: other 'that, eboma 0f th ere observed ire adenoma(a y adenomata mortem fi,,(|,,' mata occurred females as j,, >ese tumours. d maligJlai)( asbestos an* none of t)1(. nours at Sites 9 Malifr. "an 1 ther tumours t4 158 7 J 77 9a :e between s treated * detail is `s with all he largest and conre ovary, rols, and rgans, 11 Towever, alignant thelioma rcinoma rcinoma EFFECTS OF INHALATION OF ASBESTOS IN RATS Table IX.--Sites of Tumours Other than Lung Asbestos treated Control Site/Tumour type Digestive organs and peritoneum Bone and skin Breast Ovary Other female gemto-urinary organs Male genito-urinary organs Intracranial Thymoma Lymphoma/leukaemia Others Benign 4 3 100 3 2 3 173 7 Malignant 3 4 0 7 8 8 1 1 63 thyroid mediastinum adrenal (4) salivary gland thyroid Benign 1 0 20 0 0 0 34 0 1 suprarenal 267 ,,f the lung had a mesothelioma tunica from the worn hammer of the mill used vaginalis. Mesotheliomata of the vagin- to produce the respirable fibre could .,|is were seen in this and one other rat; have been a factor in the causation of ilirre is no evidence to suggest an associa- the tumours. However, our results now ,jon with exposure to asbestos. Also, show that there is no need to invoke in some cases there were secondaries, for such a hypothesis to explain the high example, a synovioma had spread to the rate of lung tumours. lung. In all such cases tumours have The amount of chrysotile retained in been classified by the primary site and the lungs did not show any clear increase in the few cases of multiple malignant with dose in rats exposed for longer tumours there was no difficulty in recog than 3 months. In two earlier experi nizing the distinct types, i.e. one was ments (Wagner and Skidmore, 1965; not a secondary of the other. Morris et al., 1967) a higher airborne dust concentration was used to give a DISCUSSION cumulative dose in 6 weeks similar to that given in the present experiment Our finding that the asbestosis pro over 3 months. The weight of asbestos duced by exposure progressed after cessa found in the lungs of rats exposed to tion of exposure is in agreement with amphibole was 3 times greater than in human experience but contrasts with those exposed to chrysotile. In the the early inhalation experiments reported present experiments the ratio was 6 to 1 by Vorwald, Durkan and Pratt (1951) after 3 months, but increased with in which progression did not occur. continuing exposure as the weight of Wagner (1963) reported more asbestosis amphibole in the lungs continued to with amosite than with chrysotile in increase, but the amount of chrysotile guinea-pigs, rats and monkeys but our did not. The previous experiments had experiments show that of the UICC shown that the rate of elimination of standard reference samples amosite is the dust from the lungs was much greater least fibrogenic in rats. for chrysotile than for the amphiboles. Gross et al. (1967) found lung cancers The present results may be explained on in 25 of 72 rats which survived 16 months' this basis, the weight of chrysotile having exposure to chrysotile dust at a mean reached equilibrium level, i.e. the rate of concentration of 86 mg/m3 for 30 hours elimination equalling the rate of retention. a week. They considered that contami There are a number of features of the nation of the asbestos by trace metals results presented above which we found I