The field of environmental toxicology has become quite important to the study of environmental health in human beings. The stability of the ecosystem in which we live is threatened by the nearly 5 million chemical compounds that have been synthesized worldwide, many of which have real or potentially toxic effects on the environment and on life forms. Four major groups of chemicals-metallic elements, nonmetallic elements, organic compounds and inorganic compounds-have certain agents within them that are known toxins to human beings. Some of these agents have an as yet unknown effect, whereas others have been well characterized. They can be found in the workplace, home, and outdoors, and many are unseen and odorless. In the past, most agents have been described in terms of their carcinogenic potential or major toxic effects on organ systems. It is now likely that the important characterization of some of these agents referrable to the upper aerodigestive tract should be at their receptor sites and identify the very discrete and small effects on these sites and their cumulative effects. The concept of threshold is probably an arbitrary one because to date these discrete effects have not been studied. Susceptibility on an individual basis probably varies from low to high, depending on the patient's immunologic and defense mechanisms and the existence of congenital or acquired risk factors. New attention must be given to more subtle effects on the upper aerodigestive tract (i.e., sinusitis and laryngitis) in view of the potential effects of certain toxic agents on these tissues.
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