 |  Environmental Science: A Global Concern, 7/e William P. Cunningham,
University of Minnesota
Mary Ann Cunningham,
Vassar College
Barbara Woodworth Saigo,
St. Cloud State University
Environmental Health and Toxicology
BE ALERT FOR: Determining Toxicity
Many factors interact to determine the danger posed by a given chemical, not all of which are related to the toxic agent itself. Those features that do relate to the agent include not only its level of chemical reactivity but also its physical state. Most substances must be dissolved before they can harm organisms. A potentially highly toxic substance may be benign in the solid state.
Substances soluble in water are particularly mobile because water is the medium of life inside organisms, and water is also prevalent in the environment. Fat- or oil-soluble substances have greater difficulty traveling in an aqueous medium, but once they get inside a body, some become concentrated in body tissues, building to much higher levels than are present in the external environment. This bioaccumulation and related biomagnification can greatly intensify the risks of this type of toxin. Also, some chemicals are very unstable, disintegrating to nontoxic by-products in a matter of days or weeks, while others retain toxicity for years.
Other factors influencing toxicity relate to the nature of the exposure. Dose concentration and how long the organism was exposed all make a difference. Organisms do have some ability to fend off toxins. Those mechanisms apparently have resulted from natural selection acting on ancestral generations.
BE ALERT FOR: Assessing Risk
Alas, assessing risk is not entirely a rational matter of toxicity tests and other statistical measures. We have a surprising number of biases that cause us to significantly misestimate the actual risks to which we are exposed. Some biases are rooted in our view of the world. We tend to distrust certain technologies, such as nuclear power, and so overestimate the danger. We downplay risks associated with activities we enjoy or those from which we realize social or economic benefit. We also tend to underestimate risks related to things we are familiar with or that we control, such as cars and tools.
Media coverage of sensational or violent events typically leads us to overestimate our risks from plane crashes, murder, and the like.
Finally, the concepts of probability are poorly understood by many people, making it difficult to use the concept in making valid judgments about risk. A parent driving to school with a child unrestrained by a car seat (high relative risk to the child) to protest the risk to her child posed by a classmate with AIDS (low relative risk to the child) illustrates the irrationality those foibles foster in us.
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2003 McGraw-Hill Higher Education