outbreaks of disease substantially impair the ability of epidemiologists to obtain unbiased information on past exposure. Experts who are privy to the discovery process may acquire useful information, but this information may not be available in the peer-reviewed literature on which most scientists rely. In response to these pressures, the legal arena is fundamentally shifting its use of the definitions of causation applied to epidemiologic study and to environmental issues broadly conceived. The recent proliferation of mass exposure cases, such as the Agent Orange litigation, and the class action lawsuits and courtmaster reviews on asbestos, the Dalkon Shield, and DDT contamination, are forcing a fundamental reassessment not only of traditional causation standards, but of the underlying concept of causation (Schuck, 1991). Where case law previously resisted reliance on probabilistic and statistical information, such as that generated by epidemiologic studies, recent decisions have accepted this line of evidence.

The Committee on Environmental Epidemiology recognizes that, whether in law or science, the inference of causation must be understood as a process that involves judgment and interpretation. Because the basic mechanisms of most modern chronic diseases are not well understood, analysts are forced to interpret observational data to find clues about etiology. Despite the immense public interest in the effect of hazardous wastes on public health, rather few empirical data are available. Nevertheless, public health policy requires that decisions be made despite the incomplete evidence, with the aim of protecting public health in the future.

HISTORICAL CONTEXT OF THE STUDY

Lethal episodes of severe air pollution, such as those in Donora, Pennsylvania in 1948; London in 1952; and the Meuse Valley in 1930, raised public consciousness about environmental epidemiology. The London episode led directly to the British Clean Air Act in the 1950s. The environmental decade of the 1970s included the passage of a host of laws intended to address, prevent, or control such major environmental pollution problems in the United States. Subsequently, incidents at Love Canal; Michigan feed contamination with the fire retardant chemical polybrominated biphenyls (PBBs); the James River; the Hudson River pollution with the pesticide kepone; Times Beach, Missouri; Bhopal, India; and most recently burning Kuwaiti oilfields and oil spills have provided the global village with vivid images of devastating pollution.

In response to concerns spawned by several of these earlier episodes, Congress passed laws that included requirements for scientific



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