Document 9anKVKa9m46yYKqz21pvbvo5

the : di- the hich i As;eons ;socikirlc, EngiPhD, i Florthere : epi.:nics m have lulf of identic, dengue | United . nsville, !I id sub- J ? is en. of St`. ( i report- 1 dogous ^ rart of ;al sani in an ie to po-' rggested. is solved ieal News 1 jOESLAL. 'OF*'.THE* AKaqCAT!'-* .MEDICAL ASSOCIATION - June 9, 1969 * . Environmental Asbestos: Threat or Phanfrom The paradox of asbestos is that although its primary uses have been for safety--in fire insulation and vehicle brake linings--it now is widely condemned as a hazard to man's lungs. The association seems strong, several investigators have said, between long-time inditstrial ex posure to asbestos and certain bronchial diseases, including pleural mesothelioma. Based on what is known, how ever, the fears about asbestos' presence in the environment seem exaggerated, said George W. Wright, MD, head, Department of Medical Research, St. Luke's Hospital, Cleveland. He spoke at the American Thoracic Society meeting in Miami Beach. The goal for the next few years, he said, should be more research about safe ways to use asbestos. 'This is the only sure way to combat unwarranted apprehen sion and speculation." Use Increased Asbestos use has increased in recent years, but most of the ad ditional material has gone into products which tightly bind the fibers, preventing their escape into the atmosphere. These in clude asbestos tile and cement. Some asbestos-containing prod ucts do wear, however, and the fibers are released. These include brake lining3, siding, and shingles. The fibers that might be re leased from all kinds of ''wear'' either become bound into the soil or are captured in rain or clean ing water. Asbestos is almost universally present in river water, but in very small amounts. That asbestos is indestructible is a fallacious concept, "and the belief that it accumulates on the surface of streets, etc., seems illfounded and will require some proof," Dr. Wright said. Less than 5% of US asbestos production goes into brake lin ings. The high heat of friction destroys the asbestos, converting it into an amorphous material, forsterite. "Of the total materials removed from brake linings during their use, less than 5% appears as ac tual asbestos. The number of as bestos fibers released by normal friction material wear must be small indeed," the Cleveland in vestigator commented. If asbestos fibers are in the air breathed by the general public, the rare occurrence of pleural mesothelioma unrelated to occu pation "strongly suggests that there is a tolerable level of air borne asbestos fiber." Structures similar to asbestos bodies have been found in 25% or more of the general public, ac cording to autopsy studies. But these structures have not been proven to be asbestos. At least 20 widely disseminated substances are capable of form ing these structures in lungs, he said. One of the most common, in wider use than asbestos, is talcum powder. So far, no laboratory method has been developed to determine which ferruginous bodies in a lung are asbestos. Until one is developed, asbestos should not be blamed for all the fibrous materi al found in lungs, Dr. Wright said. Miners Surfer Pleural Damage In a group of Canadian asbestos miners with parenchymal disease, pulmonary function was invaria bly more impaired in the pres ence of pleural disease, reports Margaret R. Becklake, MD, as sociate professor of epidemiology and health, McGill University, Montreal. Physicians have tended to dis regard the significance of pleural changes on pulmonary function. This study suggests that such changes have a significant effect on all aspects of lung function. When 1,069 asbestos workers were surveyed, marked pulmo nary fibrosis was found in 1.4%. All were men over age 55. The degree of parenchymal disease was rated according to radiological findings. When pleural disease also was present, pulmonary function was invaria bly less by every measurementlung volume, flow rate, and dif fusing capacity at rest and during exercise. The effects of pleural changes in restricting lung volume were expected. `The consistent asso ciation of gas-exchange impair ment with the presence of pleural changes suggests that free move ment between lung and chest wall is necessary to preserve optimal ventilation to perfusion imbal ance," Dr. Becklake said. "In other words," she contin ued, "free pleural movement ap pears to be necessary for normal gas-exchange." Exposure to asbestos dust may result in diffuse generalized pul monary fibrosis. The pleural changes (thickening and/or pleural calcification) are a com mon finding among workers ex posed to asbestos dust. In regard to pleural plaques, George W. Wright, MD, S3id "in an area where asbestos fiber is known to be present in consider able concentration i such as east ern Quebec) ... it is proper to consider these findings as evi dence of asbestos exposure." There is no evidence associat ing the presence of pleural plaques with development of the much more serious disease, meso thelioma, however. ___ PRODUCED JAMA, June 9. 1969 Vol 203. No 10 1735