Monday 23 March 2009
The magnitude and extent of illness related to environmental exposures are difficult to ascertain. The Environmental Protection Agency estimates that more than 80,000 chemicals are currently used in the United States; approximately 1500 are pesticides and 5500 are food additives that affect our water and food supplies.
Although only 600 of these chemicals have been tested, 10% have produced cancer in at least one rodent species.2 Industrial chemicals, production byproducts, and metals are commonly detected at hazardous waste sites.
There are currently 11,300 Superfund-designated waste sites in the United States. The potential human health hazards associated with exposure to chemical mixtures is a major concern.
There is considerable difference in the magnitudes of exposure in the occupational and environmental settings. Occupational exposures affect a defined cohort of workers who are exposed to chemicals in the range of parts per million (ppm); by contrast, environmental exposures to these same chemicals in the air, water, or hazardous waste sites may be in the parts per billion (ppb) or parts per trillion (ppt) range. The health effects of such chronic, low-level exposures are unknown.
In the United States, four regulatory agencies determine exposure limits for environmental and occupational hazards: the Environmental Protection Agency, the Food and Drug Administration (FDA), the Occupational Safety and Health Administration, and the Consumer Products Safety Commission.
The Environmental Protection Agency regulates exposure to pesticides, toxic chemicals, water and air pollutants, and hazardous wastes. The FDA regulates drugs, medical devices, food additives, and cosmetics. The Occupational Safety and Health Administration mandates that employers (including hospitals and physicians) provide safe working conditions for employees. All other products sold for use in homes, schools, or recreation are regulated by the Consumer Products Safety Commission.
Physicians should be familiar with current approaches used by regulatory agencies in the United States and be prepared to explain the strengths and limitations of the scientific evidence in nontechnical terms.
Health care providers must be prepared to counsel patients about the primary prevention of disease related to occupational and environmental exposures, taking into account potential synergistic effects of mixed exposures and individual genetic susceptibility.
Prevention of tobacco smoking would prevent 80% to 90% of lung cancers; how-ever, this objective has been difficult to achieve, especially in teenagers. Strategies for secondary prevention of lung cancer in former or current smokers (e.g., chemoprevention) have been disappointing so far.
Prevention of occupationally related diseases rests on defining and enforcing safe exposure levels, developing new technologies to reduce industrial exposures, and identifying less toxic substitutes for industrial and chemical agents. These strategies require a basic understanding of biochemical and molecular mechanisms of toxicity.