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Health hazards of asL'estos J. C. GILSON* Inhaled fibres of asbestos can cause fibrosis of the lungs and two kinds of cancer. Protection of asbestos workers calls for monitoring and controlling their working environment and linking these records with records of their health HISTORICAL Asbestos was the first inorganic fibre tn be used in compo sites. More than 4000 years ago clay pots in Finland were strengthened by adding anthophyllite fibres1. In classical times asbestos doth was used to preserve the ashes of the eminent. The oldest known piece of asbestos duth from the New World, dating 'from about 1740. is a small purse made of tremolite in the Sir Hans Sloane collection of minerals in the British Museum (Natural History). The modern asbestos industry is about 100 years old. suning nearly simultaneously in Canada and die USSR. b'i: it was not unri> 30 vears later that the first medical reports appeared in France and England, indicating that there might be a specific type of damage to the lungs following inhalation of the dust. By the late 1920s it was clear from surveys made in this country and in USA1,1 that a high proportion of older workers in' the asbestos textile industries were becoming severely disabled by a specific type of chest disease due to the dust. This was named asbestosis. O/SEASES CAUSED BY ASBESTOS DUST Research carried out in the 1930s, supported by the greatly expanded investigations during the last IS years into the types of disease caused by asbestos, now.provides a much clearer picture of the specific hazards and how damage to health can be avoided in the future. Table 1 lists the diseases. TiH* 1 :iuih By utMnoi dun kitettou Cams . Fiurosrs at lungs Bronchial (lungl Mesothelioma Skin Asbestosis It: asbcstv.is the dust causes scarring and thickening '! ilic i:s>ue> of '!x lung The iwn parts particularly aliecu d j-.' Mr f::..-%! jir pavjsC* (re-.pirakiry bronchioles) ur.eic thc\ --inch i: ;c the i.-rr'.in.sl mr sacs tthe alveolu. and the s ;;i.'.'c n; ;Ji. lu.-.g (pieuijl. The thickening of the h\ the .' 'csioj dust allcci.s me hnictun. o' the ' M'-c II:.- volume when fully infuMj v U.: : - '.i.i ii-j >n i' les, ilun noinui. "I he V .-- ... ... w ... na : i.i'nu'M' l ml. I t.iiut<4ia!; I ; I. I \V. . ( K i\rt become stiffer than normal so that the compliance is reduced. The thickening in the alveolar walls, when the disease is extensive, also reduces the gas transfer for oxygen, so that the blood leaving the lung is no longer folly saturated with this gas. The transfer of carbon dioxide from the blood to the air. in the lungs is not, however, sppre- ciably affected. The reduced oxygen transfer is partly compensated for by an increase in the frequency of breath* ing so that the subject notices breathlessness on slight exertion. These alterations of lung function are used to assist in diagnosis of asbestosis and measure the severity of the damage. _ ksbesto'is takes a number of years to develop, even under very dusty conditions, but once established it is a progressive disease not materially affected by avoiding further dust exposure. The less the dust exposure, the longer interval before the onset of disease, the leas its severity; and the less chance of being affected. Thir dose response relationship is used to fix the acceptable dust levels - threshold limit values -- for those working with asbestos. The article by Holmes in this issue describes how these standards are applied in practice. Prevention by avoiding exposures (o a dangerous quantity of dust ts an essential step towards the safe use of asbestos. Asbestos cancers Some years after the recognition of asbestosis as an isnpor* tant problem in the asbestos textile industry, articles began to appear in the medical journals4 suggesting an association between asbestosis and lung-cancer. A survey in I95S firmly established that those who had worked in the asbestos textile industry before the improvements in dust control, introduced in the 1930s, had a 10-fold excess risk of developing lung cancer5. The survey, however, also indicated that the improvement in dust control introduced at a particular factory after 1933 had very materially reduced the risk. Later surveys at this factory have confirmed this6. The lung cancers seen in asbestos woikers are similar to those caused by cigarette smoking. Recent research imii* cates that there is likely to he a synergistic effect of cigarette smoking and exposure to asbestos dust1. The precise quantitative inier-rclauonship between asbestos. c;C'reue>. and other factors is not fully established, but present evidence indicates that those who smoke cigarettes a d me exposed to asbestos dust have a risk of developing h;::.: cancer at least fifty times etcater than ncn-snioaeis \u;' kre not exposed to asbestos dust-- In the last years thete has been much new infemta* in-:: about the hul. between c.\pn>uie to asbestos and tiMi!:-.4] piov;.iu>h verx tare type of cancer afteeting the