Chapter Summary

Health is a state of physical, mental, and social well-being, not merely the absence of disease or infirmity. The cause or development of nearly every human disease is at least partly related to environmental factors. For most people in the world, the greatest health threat in the environment is still, as it always has been, from pathogenic organisms. Bacteria, viruses, protozoa, parasitic worms, and other infectious agents probably kill more people each year than any other cause of death. Highly lethal emergent diseases such as Ebola and AIDS along with newly drug-resistant forms of old diseases are an increasing worry everywhere in the world.

Stress, diet, and lifestyle also are important health factors. Our social or cultural environment may be as important as our physical environment in determining the state of our health. People in some areas in the world live exceptionally long and healthful lives. We might be able to learn from them how to do so as well.

Estimating the potential health risk from exposure to specific environmental factors is difficult because information on the precise dose, length and method of exposure, and possible interactions between the chemical in question and other potential toxins to which the population may have been exposed is often lacking. In addition, individuals have different levels of sensitivity and response to a particular toxin and are further affected by general health condition, age, and sex.

The distribution and fate of materials in the environment depend on their physical characteristics and the processes that transport, alter, destroy, or immobilize them. Uptake of toxins into organisms can result in accumulation in tissues and transfer from one organism to another.

Estimates of health risks for large, diverse populations exposed to very low doses of extremely toxic materials are inexact because of biological variation, experimental error, and the necessity of extrapolating from results with small numbers of laboratory animals. In the end, we are left with unanswered questions. Which are the most dangerous environmental factors that we face? How can we evaluate the hazards of all the natural and synthetic chemicals that now exist? What risks are acceptable? We have not yet solved these problems or answered all the questions raised in this chapter, but it is important that these issues be discussed and considered seriously.