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Pathology => Human Diseases => Environmental and Occupational Diseases
Environmental and Occupational Diseases
INTRODUCTION
Environmental and Occupational Diseases, illnesses caused by exposure to disease-causing agents in the environment, as opposed to illnesses related primarily to an individual's genetic makeup or to immunological malfunctions. In everyday use, the term environmental disease is confined to noninfectious diseases and to diseases caused largely by exposures beyond the immediate control of the individual; the latter restriction eliminates diseases related to personal habits such as smoking or to the use or abuse of medications or drugs such as alcohol. Occupational disease, a major category of environmental disease, refers to illness resulting from job-related exposures.
Historically, awareness of environmental diseases began with the recognition of occupational illnesses, because exposures are usually more intense in work settings than in the general environment and therefore can more readily produce overt illnesses. Examples include silicosis, a lung disease of miners, industrial workers, and potters exposed to silica dust; scrotal skin cancer in chimney sweeps exposed to soot; neurological disease in potters exposed to lead glazes; and bone disease in workers exposed to phosphorus in the manufacture of matches. Many such diseases first gained public attention during the Industrial Revolution in the 19th century.
CAUSES
Environmental diseases are caused by chemical agents, radiation, and physical hazards. The effects of exposure, in both natural and work settings, are greatly influenced by the exposure routes: primarily air pollution and water pollution, contaminated food, and direct contact with toxins. Synergistic effects-two or more toxic exposures acting together-are also important, as illustrated by the greatly increased risk of lung cancer in asbestos workers who smoke cigarettes. The potential interaction of multiple hazardous chemicals at toxic waste dumps poses a current public health problem that is of unknown dimensions.
° Chemicals
Industrial society has introduced or increased human exposure to thousands of chemicals in the environment. Examples are inorganic materials such as lead, mercury, arsenic, cadmium, and asbestos, and organic substances such as polychlorinated biphenyls (PCBs), vinyl chloride, and the pesticide DDT. Of particular concern is the delayed potential for these chemicals to produce cancer, as in the cases of lung cancer and mesothelioma caused by asbestos, liver cancer caused by vinyl chloride, and leukemia caused by benzene. Minamata disease, caused by food contaminated with mercury, and Yusho disease, from food contaminated with chlorinated furans, are examples of acute toxic illnesses occurring in nonoccupational settings.
The full toxic potential of most environmental chemicals has not been completely tested. The extent and frequency of an illness are related to the dose of toxin, in degrees depending on the toxin. For chronic or delayed effects such as cancer or adverse reproductive effects, no "safe" dose threshold may exist below which disease is not produced. Thus, the cancer-producing potential of ubiquitous environmental contaminants such as DDT or the PCBs remains undefined.
° Radiation
Ionizing and nonionizing radiation can produce both acute and chronic health effects, depending on dose levels. The effects of nonionizing radiation at lower dose levels are uncertain at present. Ionizing radiation at high doses causes both acute disease and delayed effects such as cancer. Victims include workers exposed to various occupational use of X rays or radioactive materials. Although the disease-producing potential of ionizing radiation at low doses is also uncertain, an increase in chromosome damage has been observed in workers in nuclear shipyards.
° Physical Hazards
Major physical hazards include traumatic injuries and noise. Trauma arising from unsafe environments accounts for a large proportion of preventable human illness, and noise in the workplace is responsible for the most prevalent occupational impairment: hearing loss or permanent deafness.
FORMS OF ENVIRONMENTAL DISEASE
Environmental diseases can affect any organ system of the body. How the diseases are expressed depends on how the particular environmental agent enters the body, how it is metabolized, and by what route it is excreted. The skin, lungs, liver, kidneys, and nervous system are commonly affected by different agents in different settings. Of particular concern is the capacity of many environmental agents to cause various cancers, birth defects or spontaneous abortions (through fetal exposure), and mutations in germ cells, the last-named raising possibilities of environmentally caused genetic diseases in later generations.
Environmental illnesses can be mild or severe and can range from transient to chronic, depending on the doses of toxin received. Some diseases occur abruptly after a toxic exposure, whereas the time of onset of other diseases varies after exposure. Environmentally induced cancers, for example, commonly involve latency periods of 15 to 30 years or more. Those illnesses that occur directly after a distinct toxic exposure are usually easily identified as being environmentally or occupationally caused. If the exposure is not clear-cut or illness is delayed, however, the cause is difficult to identify, as clinical features alone are usually nonspecific. In addition, many different causes, environmental or otherwise, may produce identical illnesses. In such instances, epidemiological studies of exposed populations can help relate exposures to the illnesses they cause.
OCCURRENCE
Total frequencies of environmental illness are difficult to measure because of the reasons just described. When causes can be identified, however, scientists observe that frequencies of occurrence of a particular illness vary directly with the severity and extent of exposure. Particularly frequent in the workplace are skin lesions from many different causes and pulmonary diseases related to the inhalation of various dusts, such as coal dust (black lung), cotton dust (brown lung), asbestos fibers (asbestosis), and silica dust (silicosis). Environmental agents can also cause biological effects without overt clinical illness (for example, chromosome damage from irradiation). The health significance of such subclinical changes is not yet clear.
AGENCIES AND LAWS
The regulation of workplace practices and of potential environmental pollution has evolved as the use of chemicals and human exposure to potential toxins have grown more widespread and complex in modern society. In the United States, numerous laws are directed at protecting occupational and environmental health. Most were passed since 1960, including the Occupational Safety and Health Act of 1970 and the Resource Conservation and Recovery Act of 1979. Means for the rapid cleanup of toxic waste dumps were provided in the Comprehensive Environmental Response, Compensation, and Liability Act of 1980.
Federal agencies responsible for enforcing such environmental and occupational health laws consist principally of the Environmental Protection Agency and the Occupational Safety and Health Administration (OSHA) within the Department of Labor. The Food and Drug Administration, within the Department of Health and Human Services (HHS), and the Department of Agriculture have regulatory responsibility for preventing the contamination of food supplies. Federal field investigations of potential environmental and occupational hazards are handled through the Center for Environmental Health and the National Institute for Occupational Safety and Health, which are components of the Centers for Disease Control, within HHS. General environmental health research and toxicological testing are directed through the National Institutes of Health and the National Toxicology Program, also within HHS. Comparable regulations and agencies at state and local levels, working with their federal counterparts, play a crucial role as well.
International coordination of environmental and occupational control activities in many countries is guided through the World Health Organization. In the developing parts of the world, such activities are of critical importance as modern industrialization proceeds in the face of poverty and growing populations.
CURRENT RESEARCH
Current trends in research in this field focus on the relation of low-dose exposures to human health, the influence of environmental toxins on both male and female reproductive functions, and the potential health implications of subclinical indications of biological damage (for example, genetic or chromosomal damage). In such research, increased emphasis is being placed on delayed or long-term health effects and on a wide range of potential synergistic interactions between environments and hosts.
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