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SRA
Risk Science & Law Specialty Group |
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| 1999-2000
Online Casebook (Second Edition)
In re Hanford Nuclear Reservation Litigation Can a simple statistical risk threshold be applied as a legal standard to establish general causation? Should animal evidence of chemical carcinogenicity be admitted to determine general causation in the face of abundant human (epidemiological) evidence? Can the evidence of actual exposure, dose and risk from toxic chemicals used to determine individual causation be so complex that a jury could be misled into a wrong judgment? Approximately 3,000 plaintiffs in this consolidated litigation alleged either current or future toxic injury (E.D. Wash. August 21, 1998; unreported but opinion available at www.hanford. gov/docs/ruling). Claims included thyroid, gastrointestinal (GI) and other cancers, as well as thyroid disease, as a result of exposure to radioactive Iodine-131 and Plutonium-239, and also to nonradioactive emissions from the Hanford Nuclear Reservation in Washington State. Threshold for a finding of general causation. In this 762-page order granting partial summary judgment to the defendants—the federal government and its contractors, the court resolved the general causation phase of the litigation by adopting a minimum risk ratio of 2.0. That is to say: § Causation could be inferred where an exposed population carries at least twice the risk of a specified disease compared to an unexposed population. § The strict "doubling of risk" threshold could serve as the legal standard for testing the sufficiency of evidence pertaining to radiation exposure and for determining which claims should be heard by a jury. Reliability of extrapolations from animal evidence. Plaintiffs' claims of GI cancer from exposure to hexavalent chromium (Cr-VI) in drinking water from the Columbia River were handled differently. The court first considered whether it is scientifically proper for a plaintiff's expert to extrapolate from animal data to reach an opinion that Cr-VI is capable of causing GI cancer in humans. In the face of abundant and relevant epidemiological data, it appeared that dismissal of animal data could be justified by the court. However, where there is no relevant epidemiological evidence, as in this case, the court left open the possibility that scientifically reliable animal data might be adequate to support a finding that a chemical is capable of causing human disease. In the current case, however, the specific animal data for Cr-VI was found not to be reliable. Misleading a jury with overly complex numerical evidence. Referring to the U.S. Supreme Court's Daubert decision and the trial court's role of gatekeeper, this court observed The complexity of evidence in this case, indeed the mere appearance of complexity and the manipulation of numbers in some instances, could easily inspire the most astute jury to reach an erroneous conclusion that exposure to Hanford emissions was a cause in fact of an individual's disease. The court also excluded, under this standard, the dose reconstruction reports of several of the plaintiffs' experts. The issue of misleading complexity, in particular, may prove influential in shaping future decisions on admissibility of convoluted statistical arguments. [Contributed by Susan Rieth and John Applegate/Edited by Wayne Roth-Nelson] |
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