Low level exposure to asbestos: is there a cancer risk?

Editorial Low level exposure to asbestos: is there a cancer risk? In the early days of asbestos use when its harmful potential was not understood hygiene standards at the workplace were extremely low. Airborne dust concentrations were uncontrolled and fibre levels in excess of 100 per ml were not unusual. This type ofexposure led to the discovery that inhalation of asbestos produced pulmonary fibrosis,' bronchial carcinoma,2 and mesothelioma.3 Efforts to reduce concentrations of asbestos fibre began in the 1930s and, since the 1950s, increasingly stringent limits have been imposed by law. Some countries have banned many uses of asbestos, although it remains almost essential for some special packing and friction products. Various fibre substitutes have been introduced in advanced countries , especially for plastic or cement products, though these are generally less durable and more costly. The latter point is a serious matter in third world countries where asbestos cement products are well-nigh essential for water and drainage pipes and for building construction. In addition, it now seems possible that some manmade mineral fibres could carry similar risks to health.4 The use of asbestos today in the developed world may only be undertaken under strict control, in most countries at levels of I fibre/ml or less. Exposure levels in buildings and in the general environment of our cities, resulting from the use of asbestos products, are far lower still. The question of whether such low occupational and environmental exposures are free from risk has become a major practical, social, and legal issue. As it is apparent that controlling dust has largely eliminated the risk of pulmonary asbestosis, the main concern is now over cancer and whether or not there is a safe threshold below which asbestos does not cause tumour production. Evidence on this matter is afforded by both experimental studies in laboratory animals and epidemiological studies in human populations exposed to asbestos. Both approaches have their limitations. Animals may be exposed to measured doses of asbestos but their short life span makes direct extrapolation of the results to man difficult. Epidemiological studies, on the other hand, suffer from great uncertainty about the precise nature and intensity of exposure, especially in the distant past. Whereas the impossibility of proving a complete negative is accepted, both the epidemiological and experimental findings provide a basis for rational decisions. Experimental studies have shown that the pathological effects of asbestos depend not only on …