PRINCIPLES OF TOXICOLOGY - Biology East Borneo

9.3 SUMMARY 185Industrially Related or Occupational AsthmaMany individuals develop asthma following workplace exposure, and some asthmatics suffer additionalprovocation following the inhalation of certain industrial toxins. The inhalation of wood dusts,for instance, has been implicated in both situations. Some grocery workers have developed an asthmaticcondition following the wrapping of meats with plastic film. Apparently, heating the plastic to seal itreleases toluene diisocyanate, which is then inhaled. Subsequent exposure to even very low levels ofthe plastic, or its component, may result in a severe reoccurrence of symptoms.It has been shown that the bronchiolar muscles of asthmatics will undergo constriction at a lowerconcentration of inhaled industrial chemicals than will those of nonasthmatics. Not surprisingly, theseindividuals often find themselves reacting in situations in which their co-workers do not respond. Afurther complication for these workers is that exercise tends to exacerbate the asthma symptoms.Physical exertion, obviously required in many industrial situations, along with the simultaneouslychemical exposure can lead to severe complications for the affected worker.Lung CancerUntil the twentieth century, lung cancer was relatively rare. The rapid promotion of lung cancer to thenumber one cancer killer is directly related to the inhalation of tobacco smoke (probably 80–90 percentof all lung cancers) and industrial/atmospheric chemicals. The relationship between tobacco smokeinhalation and lung cancer was discussed previously. Many industrial chemicals have also been linkedto lung cancer in workers and laboratory animal studies.The dusts and fumes of many metals have been demonstrated to be carcinogenic in lung tissue.Epidemiologic studies conducted on worker populations in smelting operations have long showndefinitive relationships between metal inhalation and lung cancer. Industrial metal carcinogens includenickel, arsenic, cadmium, chromium, and beryllium. Workers in mining operations, including metalrecovery from ores, are at risk for developing lung cancers because of exposure to certain metals suchas chromium and uranium. The inhalation of benzo(a)pyrene and other polycyclic aromatic hydrocarbons,from coke oven emissions, has also been linked to the development of lung cancer.Radioactive materials have long been recognized as inducers of lung cancer. Uranium miners havean elevated incidence of lung cancers, as did the victims of the atomic bomb explosions at Hiroshimaand Nagasaki. Recently, the potential for inhalation of radon gas has become a concern, due to thelarge population with the possibility for long-term exposure. Smoking has been shown to exacerbatethe incidence of lung cancer when in conjunction with exposure to radioactive materials.An important feature regarding the development of lung cancer in humans is the generally longlatent period. Normally it takes 20–40 years following the inhalation of most toxins before lung tumorsappear. For this reason, it is often difficult to establish the definitive etiology of the lung cancer. Cancerof the upper respiratory tract does occur and is associated with some professions, such as chromateand nickel industry workers. By far, though, the majority of respiratory system cancers occur in thebronchioles and the lung tissues.9.3 SUMMARYThe lungs provide a unique pathway for industrial toxins and tobacco smoke to enter the body, sincethe interface between the alveolar air and the pulmonary blood can facilitate the diffusion of bothlife-giving air and life-threatening toxins. The beautiful design of the respiratory system provides anumber of highly efficient methods of protection from commonly encountered potential toxins,including• Humidification and temperature control• The mucociliary escalator