Perspective on Rsk-Rice

Perspective on Rsk-Rice - PERSPECTIVES ON RISK I. Challenge...

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PERSPECTIVES ON RISK I. Challenge of Quantitation A. Heptachlor and chlordane B. Food dyes II. Animal Testing Models A. Threshold (noncarcinogens) B. Linear (genotoxic carcinogens) C. Human Exposure/Rodent Potency index We are unavoidably exposed to hazardous chemicals, usually at low levels. A variety of attitudes toward such exposures are prevalent in the population. On the one hand, we see a pessimistic or fatalistic view expressed by some that this menace, fueled by population increases, will inevitably destroy the ecosystem and us with it. Alternately, some observers present an optimistic viewpoint that the consequences will be minimal; they may even glorify risk in general as a challenge with selective value. For example, a publication by Dow Chemical entitled Life Is In The Balance: Weighing the Questions of Risk and Benefit in Today’s World starts with a quotation by Helen Keller (1902). “Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoidance of danger is no safer in the long run than outright exposure. Life is a daring adventure, or nothing.” An issue inherent in the regulatory process is how to estimate the magnitude of risk so that we can decide rationally how much to spend to alleviate it. It is illuminating to examine the basis for some early regulatory decisions and to analyze how this process has changed with experience. The bottom line is that regulations are based on estimates of risk. But results of risk calculations are acknowledged to have very large uncertainties, limiting the effectiveness of the regulatory system. To reduce these uncertainties, better methods to extrapolate among species and, ultimately, better understanding of toxic mechanisms are needed. In 1975, the EPA banned for general use the chlorinated hydrocarbons chlordane and heptachlor on the grounds these pesticides presented an "imminent hazard". To fulfill its mandate to protect the environment from "unreasonable" effects, the agency based its decision on three elements. First, it was found at that time that these agents are rodent carcinogens and thus likely human carcinogens. Since virtually all known human carcinogens are animal carcinogens, it was concluded the reverse relationship also holds. Some observers, including the company manufacturing these pesticides, objected because rodent metabolism of the chemicals and thus our internal defenses against them are "totally different", thus invalidating the extrapolation. (This argument in various forms persists for many agents in risk estimation.) Second, an extrapolation to humans was made. These agents are highly persistent in the environment, and were widely distributed, being found in soil, animal feed, and human food (crops, meat). They were detectable in the adipose tissue of over 90% of the population, so exposure clearly occurred. Third, the burden of proof for safety is on the manufacturer. If danger exists, the manufacturer must show safe and effective substitutes are not available. This was
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This note was uploaded on 02/01/2010 for the course ETX etx10 taught by Professor Rontjeerderma during the Fall '09 term at UC Davis.

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Perspective on Rsk-Rice - PERSPECTIVES ON RISK I. Challenge...

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