TABLE 2.1 Common Classes of Environmental Health Hazards, with Examples











Carbon monoxide

Ionizing radiation


Repetitive motion



Electromagnetic fields



High-demand/Low-control occupations

Vinyl chloride

Temperature extremes




a This category is sometimes included in the class of physical hazards.

as runoff of agricultural fertilizers and pesticides into waterways that supply drinking water.

The environmental exposure limits designed to protect against contaminants may be in the form of regulatory standards (e.g., maximum contaminant levels (MCLs) for drinking water), action standards (e.g., soil lead levels exceeding 500 ppm), or risk-based standards (e.g., a 10-4 or 10-6 excess cancer risk). Environmental standards are often based on retrospective studies of worker exposure (a natural experimental model) or on laboratory studies using animals. A large degree of uncertainty exists when extrapolating from safe levels of exposure for workers based on an 8 hour period within a work site to ambient levels of residential exposure that may occur 24 hours a day outside the worksite (and away from safety systems such as exhaust ventilation). An even greater level of uncertainty and complexity results when studies of small laboratory animals exposed to large quantities of a single substance over a brief period of time are used as the basis for projecting health risk to humans, who are typically exposed to small quantities of multiple substances over extended periods of time.

Air pollution—both indoor and outdoor—raises another set of environmental hazards. Over 50 percent of the U.S. population lives in areas where the outdoor air did not meet EPA standards for contaminants (e.g., ozone, nitrogen dioxide, sulfur dioxide, particulates, and lead) at some time during the previous 12 months (DHHS, 1990). Most Americans spend the majority of their time indoors, either at home, school, or the workplace, where most of the exposure to foreign proteins via inhalation

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