Chapter 30
Risk Management in the Absence of Credible Risk Assessment Perry J. Gehring
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DowElanco, 4040 Vincennes Circle, Suite 601, Indianapolis, IN 46268 Rational management of risk is inextricably linked to the ability to measure and assess the potential risk. For acute and some subchronic manifestations of toxicity produced by pesticides, this is achievable. For chronic toxicity, particularly carcinogenesis, the ability to measure a response in animal studies exists. However, the ability to assess risk from use of these data alone is a fiction. Rather, management of such risks must be based on insight and judgement. Banning all materials shown as carcinogenic in exaggerated tests or using best feasible technology to minimize exposure to the lowest possible levels are not logical alternatives. About a hundred years ago, the great British physicist and inventor, Lord William Thompson Kelvin, made a statement summarizing the uncertainty involved in human knowledge. " . . . [W]hen you can measure what you are speaking about, and express it in numbers," Kelvin said, "you know something about it; but, when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science. . . . " That simple statement, made by a man knighted for his contributions to scientific discovery, has tremendous implications for the field of risk management. To manage a given risk, we must be able to define and measure it. Unfortunately, many of the risks we face today are as yet undefinable and immeasurable. They may even be nonexistent. As a result, we tend to compensate with worst case estimates that magnify the scope of the risk, sometimes beyond all reasonable bounds. While this is intended as prudence and conservatism, the end result frequently looks more like anxiety management than the management of risk. This is particularly the case with politically sensitive areas like toxic substances and pesticides. 0097-6156/91/0446-O267$06.0OA) © 1991 American Chemical Society
Tweedy et al.; Pesticide Residues and Food Safety ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
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268
PESTICIDE RESIDUES AND FOOD SAFETY
For the most part, what we know about the risks posed by synthetic compounds like pesticides comes from work done with animals rather than from actual human experience. In fact, documented instances of adverse effects in people from trace level exposures to pesticides are rare. Despite the conventional wisdom that pesticides are inadequately tested, more toxicological and environmental studies are required to market a pesticide than almost any type of product. Toxicity evaluations for pesticides and pharmaceuticals are essentially the same in cost and stringency. Toxicity studies assess acute, subchronic, chronic, reproductive, genetic, and developmental toxicity. Environmental studies determine the rate at which the pesticide is degraded to harmless compounds and the amounts that may be translocated to unwanted sites such as food and water. These evaluations require a minimum of five years to complete and cost $10 to $15 million. Qualitatively, this battery of tests does an excellent job of revealing potential adverse effects on health and the environment. Rarely has an adverse effect escaped detection in this process. Of course, tomorrow even newer, more meaningful knowledge and technology may be developed to provide still better detection of potential adverse effects. Acute and Subchronic Toxicity However, the quantitative value of these tests is a mixed bag. For acute and subchronic effects, the battery is generally satisfactory. Risk management then involves setting up safety factors that limit exposures to acceptable levels—from one-tenth to one-one thousandth of the dose found to produce no observed effects in any of the numerous studies performed—-with the size of the safety factor depending on the severity of the effect. Often, the effect detected in the animal studies is not toxic in itself but a very subtle reaction to exposure, such as a decrease in plasma cholinesterase. That our tests are able to detect these subtle changes in metabolism serves as a hidden, built-in safety factor. The effects of actual concern generally require greater exposures. Human Exposure Human experience does not suggest a major problem in management of risks from acute and subchronic pesticide exposures. According to the National Safety Council, 21 accidental deaths in the U.S. were attributed in 1985 to agricultural, horticultural, chemical, and some pharmaceutical preparations (7). This compares with 31 deaths in 1984 and 22 deaths in 1983. For perspective, total deaths due to poisoning during these same years ranged from about 4,600 to more than 5,000. Most of these deaths were caused by accidental ingestion of drugs. Further, actuarial estimates presented in The Scientific American ranked risk from pesticides 28th on a list of 30 potential hazards (Figure 1). However, these estimates do not square with public perceptions. In a survey published in the same article, pesticides were ranked 15th out of 30 by a
Tweedy et al.; Pesticide Residues and Food Safety ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
30.
Risk Management in the Absence of Credible Risk Assessment 269
GEHRING
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