Understanding the risk resulting from exposure to a contaminant requires knowledge of both the dose that a person receives as a result of exposure and the potential health effects of the contaminant. In Chapter 9 we focused on approaches for quantifying the exposure of a person to actual or potential releases of contaminants into the environment. The next step of the risk assessment procedure is to characterize the impact of contaminant exposures on human health and make quantitative estimates of health effects. This chapter, which is the first of two dealing with consequence assessment in the context of human health, focuses on the ways in which contaminants can disrupt normal development and functions, including reproduction, in the human body. In Chapter 11 we address the methods by which the human health consequences of exposure to a contaminant are quantified.

Characterization of the potential health effects of exposure to environmental contaminants lies within the field of toxicology, which is the science that deals with "poisons" and their effects. The concept of a "poison" is described by Klaasen and Eaton (1991): "One could define a poison as any agent capable of producing a deleterious response in a biologic system." This is not, however, a useful working definition, for the very simple reason that virtually every known chemical has the potential to produce injury or death if present in sufficient amount. Paracelsus (1493-1541) phrased this well when he noted: "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy." The notion that "the dose makes the poison" is illustrated in Table 10.1, where the dose that is lethal to 50% of exposed rats is given for substances ranging from table sugar to aflatoxin.

The purpose of this chapter is to provide a condensed treatment of some of the basic biological mechanisms that give rise to toxic effects from chemicals and radiation. In many cases toxicological information on contaminants is summarized and compiled by government agencies and others. In other cases (e.g., a new industrial use of a chemical compound), additional toxicological studies might be required to characterize the risk. The information presented in this chapter is intended to assist the risk analyst in understanding the biological bases of potential toxic effects discussed in such reports.

Quantitative Environmental Risk Analysis for Human Health, by Robert A. Fjeld, Norman A. Eisenberg, and Keith L. Compton Copyright © 2007 John Wiley & Sons, Inc.

TABLE 10.1 Approximate Oral LD50 Values in Rats


LD50 (mg/kg body weight)

Sucrose (table sugar) Sodium chloride

29,700 3,000

(common salt) Vanillin Aspirin Copper sulfate Chloroform Caffeine DDT Nicotine Strychnine Sodium cyanide Aflatoxin B1

1,580 1,000 960 908

192 113 53 16 6 5

Source: Environ 1988.

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