PRINCIPLES OF TOXICOLOGY - Biology East Borneo

502 OCCUPATIONAL AND ENVIRONMENTAL HEALTHUnited States whereas in 1998 they accounted for 65 percent of all reported occupational illness. Thepercent distribution of reported occupational illnesses by category of illness for private industry in theUnited States is presented for years 1982–1998 in Table 3.20.2 CHARACTERISTICS OF OCCUPATIONAL ILLNESSHealth care providers often overlook the occupational cause of human illness. This is due to severalspecial characteristics of occupational disease that may obscure its occupational origin.1. The clinical and pathological presentation of occupational disease is often identical to that ofnonoccupational disease. For example, asthma (excessive airways narrowing in the lungs) due to airborneexposure to toluene diisocyanate is clinically indistinguishable from asthma due to other causes.2. Occupational disease may occur after the termination of exposure. An extreme example wouldbe asbestos-related mesothelioma (a cancer affecting the lining of the lung and abdomen) that canoccur 30–40 years after the exposure. Even relatively acute illness can occur after the exposure episode.Some forms of occupational asthma manifest at night, several hours after the end of the exposure.3. The clinical manifestations of occupational disease can vary with the dose and timing ofexposure. For example, at very high airborne concentrations, elemental mercury is acutely toxic to thelungs and can cause pulmonary failure. At lower levels of exposure, elemental mercury has nopathologic effect on the lungs but can have chronic adverse effects on the central and peripheral nervoussystems.4. Occupational factors can act in combination with nonoccupational factors to produce disease.A classic example is the interaction between exposure to asbestos and exposure to tobacco smoke.Long-term exposure to asbestos alone increases the risk of lung cancer about fivefold. Long-termsmoking of cigarettes increases the risk of lung cancer about 10–20-fold. When exposed to both,however, the risk of lung cancer is increased about 50–70-fold.20.3 GOALS OF OCCUPATIONAL AND ENVIRONMENTAL MEDICINEOccupational and environmental medicine is both a preventive and a clinical specialty. Preventionactivities are often divided into three categories, primary, secondary, and tertiary. Primary preventionis accomplished by reducing the risk of disease. In the occupational setting, this is most commonlydone by reducing or eliminating exposure to hazardous substances. As exposure is reduced, so is therisk of adverse health consequences. Such reductions are typically managed by industrial hygienepersonnel and are best accomplished by changes in production process or associated infrastructure.Such changes might include substitution of a safer substance for a more hazardous one, enclosure orspecial ventilation of equipment, as well as rotation of workers through areas in which hazards arepresent to reduce the dose to each worker. (Note that this method does increase the number of workersexposed to the hazard.)Secondary prevention is accomplished by identifying health problems before they become clinicallyapparent (i.e., before workers report feeling ill) and making interventions to limit the resultingdisease. This is a major goal of occupational health surveillance, which is discussed in greater detailbelow. The underlying assumption is that such early identification will result in a more favorableoutcome. An example of secondary prevention in occupational health is the measurement of bloodlead levels in workers exposed to lead. An elevated blood lead level indicates a failure of primaryprevention but can allow for corrective action before clinically apparent lead poisoning occurs.Corrective action would be to improve the primary prevention activities listed above.Tertiary prevention is accomplished by minimizing the adverse clinical effects on health of an illnessor exposure. Treatment of lead poisoning (headache, muscle and joint pain, abdominal pain, anemia,kidney dysfunction) by administration of chelating medication is an example of tertiary prevention.