Taking Chances on Risk Assessment

"Risk Assessment," Science. April 17, 1987. Vol. 236. Pages 267-300. American Association for the Advancement of Science, Washington, D.C. In its April 17 issue, Science published six lead articles on health risk assessment. Although none of the articles carefully defines the subject term, all of them use it to mean structured estimation of probability and severity of harm. Actually, the articles focus more on social risk management than on the science of risk assessment. The topics covered are central, although together they form a bit of a hodgepodge. Regrettably, the magazine carries no explanation as to the intentions of the issue or the basis for selecting these subjects or authors. If the articles have a common theme, it is a plea to intercompare different risks and set control strategies proportionate to health burden. Richard Wilson and E.A.C. Crouch set the tone by arguing, quite correctly, that risk assessments help us delineate the stakes involved in personal and social decisions. Congruent with the prevailing view of these matters, they note that scientific assessments are evaluated in light of cultural values as decisions are made. Risk estimates, they continue, gain meaning when set in context relative to commonplace risks. Unfortunately, the article doesn't clearly distinguish between the several scientific and social evaluative functions. In the most novel and provocative article, Bruce Ames, Renae Magaw and Lois Swirsky Gold propose a scheme for ranking chemical carcinogenic hazards. The scheme involves the following: testing the chemicals' cancer potency in rodent assays; taking into account the degree to which people are expected actually to be exposed to the compounds; arraying the resulting risks comparatively; recognizing from the ranking that naturally occurring substances may present risks as high as those of pesticides or other anthropogenic substances; and finally, taking the ranking into account when setting protective priorities. While I don't disagree with the proposed HERP (Human Exposure/Rodent Potency) index in principle, I am concerned that the authors may be stretching the raw data too far. They take great trouble to point out how iffy carcinogenic assays are, but then they establish the HERP ranking on just such crude potency tests. The authors state point-blank: "We lack the knowledge to do low-dose 'risk assessment,' " and caution that their scale "is not a scale of risk to humans but is only a way of setting priorities for concern." The approach is basically appealing, but its limitations must be respected. Lester Lave argues that it is easier to decide among several risky alternatives—to make "risk-risk" decisions—than to decide, on fundamental grounds, how safe something should be. "The former are self-limiting," he says, "and require an explicit balancing of the risks. The latter are subject to rhetoric about zero risk because there is no necessity to consider what is being sacrificed to lower the probability further." This isn't compelling. For well-known, circumscribed situations, risk (in X-ray screening, for instance) can be weighed against risk (of breast cancer). But for more open-ended situations, such as new technologies that offer unprecedented benefits, the question may have to be "How safe?" or "How safe at what cost?" The straw-person issue of zero risk need not be allowed to interfere. Quoting William Ruckelshaus' crack that risk assessment is the product of "a shotgun wedding between science and the law," Milton Russell and Michael Gruber, a former and a current Environmental Protection Agency official respectively, characterize the awkward product of that marriage. They describe how useful assessment is in setting priorities, tailoring regulations and making regulatory decisions at particular environmental sites. They sound a bit battle-weary, which is understandable. They also sound apologetic, which is unnecessary because in many ways the agency is performing better scientifically than ever before. It is contributing to the maturation of the risk assessment field. We all face the problem that for thousands of risks (such as chemicals) we now know just enough, scientifically, to "worry," but not enough to know how much to worry. Addressing a theme alluded to by other contributors, Paul Slovic reviews psychological research on people's expressed (dis)preferences for various risks. He reminds us that risk aversions are deeply conditioned culturally, that the public may fail to weigh risks commensurately against associated benefits, and that some debates about risks really are proxy debates about more general social issues. To me, a principal challenge for such survey research is to devise ways of inquiring not only about the negative aspects (risks and costs) of situations, but about the positive (benefits and cost-savings) as well—the two integrated. In the last article, David Okrent provides a historical review of the Nuclear Regulatory Commission's development of safety goals for power reactors. The goals, adopted in 1986, stipulate that power plants not subject members of the public to "significant additional risk" above background, and that risks from nuclear power be comparable to the risks from generating electricity by competing technologies. The policy archeology is illuminating, though dry. I wish Okrent had said more about the difficulties in translating abstract risk goals into engineering blueprints, and in proving that, probabilistic goals have been met. Science should be commended for assembling this issue. It could have avoided a few shortcomings, though. Unlike essays in Daedalus for example, the articles in this collection are somewhat repetitious and don't show much evidence that the writers took account of each other's drafts. A survey of the whole field and a projection of research and policy trends would have enhanced the contribution. Lowrance is director of the Life Sciences and Public Policy Program, The Rockefeller University, New York, NY 10021. He is the author of Modern Science and Human Values (Oxford University Press, 1986) and Of Acceptable Risk (William Kaufmann, 1976).

Taking Chances on Risk Assessment

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