PRINCIPLES OF TOXICOLOGY - Biology East Borneo

180 PULMONOTOXICITY: TOXIC EFFECTS IN THE LUNGAir-Pollutant GasesMany of the air pollutants are inhaled as gases, such as carbon monoxide, sulfur dioxide, and thevarious oxides of nitrogen. By far, the number one killer as far as toxic gases are concerned is carbonmonoxide. The incomplete burning of various fuels results in the emission of carbon monoxide, andevery year there are many deaths and injuries from individuals who breathe this gas in an enclosedspace. While some of these are suicides, there are also many industrial exposures to carbon monoxideand other combustion pollutants. A number of air pollutant gases are produced by a complex interactionof sunlight, humidity, temperature, hydrocarbons, and the oxides of nitrogen. These interactionsgenerate smog, as well as other gases such as ozone and the aldehydes.Tobacco SmokeToxicity resulting from the intentional and unintentional inhalation of tobacco smoke is an importantconsideration given its enormous magnitude of incidence, its interaction with the toxicity of otherinhaled industrial pollutants, and its representation of the toxicity of both particulates and gases. Thenumber of people who die and are significantly injured each year in the United States due to inhalationexposures to industrial chemicals cannot be stated with certainty; however, it is definitely much smallerthan the number of people who die and are experiencing diminished health status as a result of tobaccosmoke inhalation. The smoking of tobacco products causes pulmonary emphysema, chronic bronchitis,and lung cancer in many thousands of Americans each year.Interference with Pulmonary Defense Tobacco smoke inhalation results in the derangement of thepulmonary defense mechanisms necessary to protect against the inhalation of industrial toxins. It hasbeen shown that, following chronic cigarette smoking, the cilia in the mucociliary escalator becomeincreasingly paralyzed. The decrease in ciliary activity slows or prevents the removal of depositedtoxins from the nasopharyngeal and tracheobronchial regions, as the gel layer becomes more sedentary.Many of the more than 2000 components of tobacco smoke are known to be respiratory irritants, andthese irritating properties lead to an increased production of mucous in the respiratory system.Therefore, there is a decreased movement (and removal) of mucous simultaneously with an increasein mucous production. Eventually, some of the airways can become impeded and even blocked,severely limiting the respiratory volume of the affected individual. Sometimes the overworked mucousglands will increase in size sufficiently to block the airways themselves, further impeding airflow andincreasing resistance.It has been shown that the cellular defense mechanisms of the lung, particularly the alveolarmacrophages and the alveolar polymorphonuclear leukocytes, are significantly impacted by tobaccosmoke inhalation. In many cases, these cells may be killed, causing the release of proteolytic enzymes,which come in contact with the respiratory membrane surfaces. Pulmonary emphysema can result, ifthis process is extensive, from the severe rupturing of the septa walls. Even short of cell death, thesecells become less efficient in the removal of particulates and other toxins. Therefore, the inhalation oftoxic agents in industrial environments has the potential to exert greater toxicity in smokers than inequally exposed nonsmokers. This has been shown repeatedly for many exposures to toxic chemicalsin occupational studies, such as with asbestos. For this reason, occupational epidemiologists andphysicians will often look for correlations between toxicity in an industrial worker population andtobacco use.Lung Cancer and Tobacco Smoke Bronchogenic carcinoma data from the 1980s estimated thatapproximately 90 percent of the more than 100,000 lung cancer cases each year in the United Statesare due to tobacco smoke inhalation. A very distressing aspect of this unpleasant data is that theincidence of lung cancer, previously occurring more often in men, is growing rapidly in the femalepopulation. The increasing incidence of tobacco smoke inhalation by women has been followed in anappropriate timeframe by an explosion in lung cancer cases in women. Whereas breast cancer was