Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
SCIENCE AND ITS LIMITS: THE REGULATOR'S DILEMMA 14 original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. probabilistic risk assessments: it at least has the virtue of being more faithful to the state of scientific knowledge than does the present convention. Low-Level Exposure In both examples of accidents (Bhopal and TMI-2) cited above, many people are exposed to low-level insult. The uncertainties inherent in estimating the effects of such low-level exposure are heaped on top of uncertainties in estimating the probability of the accident that might lead to the exposure in the first place. While science has exerted great effort to ascertain the shape of the dose- response curve at low doses, very little, if anything, can be said with certainty about the low dose-response. Thus, to quote the 1980 reportâThe Effects on Populations of Exposure to Low Levels of Ionizing Radiation (known as the BEIR-III report)âof the National Research Council's Committee on the Biological Effects of Ionizing Radiations, ''The Committee does not know whether dose rates of gamma or x rays of about 100 mrads/yr are detrimental to man. . . . It is unlikely that carcinogenic and teratogenic effects of doses of low- LET [linear energy transfer] radiation administered at this dose rate will be demonstrable in the foreseeable future'' (National Research Council, 1980, p. 3). This prompted Philip Handler, then president of the National Academy of Sciences, to comment in his letter transmitting the report to the Environmental Protection Agency, "It is not unusual for scientists to disagree . . . (and) . . . the sparser and less reliable the data base, the more opportunity for disagreement. . . . This report has been delayed . . . to permit time . . . to display all of the valid opinions rather than distribute a report that might create the false impression of a clear consensus where none exists" (National Research Council, 1980, p. iii). This forthright admission that science can say little about low-level insults is admirable. It represents an improvement over the unjustified assertion in the BEIR-II report of 1972 that 170 millirems per year over 30 years, if imposed on the entire U.S. population, would cause between 3,000 and 15,000 cancer deaths per year (National Research Council, 1972). I do not quarrel with the estimated upper limitâwhich amounts to 1 cancer per 2,500 man-rems; however, I regard the lower limit's being different from zero as unjustified and as having caused great harm. The proper statement should have been, at 170 millirems per year, we estimate that the upper limit for the number of cancers would be 15,000 per year; and the lower limit might be zero. Since the appearance of the BEIR reports, two other developments have added to the burden of those who must judge the carcinogenic hazard of low- level insults: (1) natural carcinogens and (2) ambiguous carcinogens.