I. Introduction

The sciences of epidemiology1 and toxicology2 are devoted to understanding the hazardous properties (the toxicity) of chemical substances. Moreover, epidemiological and toxicological studies provide information on how the seriousness and rate of occurrence of the hazard in a population (its risk) change as exposure to a particular chemical changes. To evaluate whether individuals or populations exposed to a chemical are at risk of harm,3 or have actually been harmed, the information that arises from epidemiological and toxicological studies is needed, as is the information on the exposures incurred by those individuals or populations.

Epidemiologists and toxicologists can tell us, for example, how the magnitude of risk of benzene-induced leukemia changes as exposure to benzene changes. Thus, if there is a need to understand the magnitude of the leukemia risk in populations residing near a petroleum refinery, it becomes necessary to understand the magnitude of the exposure of those populations to benzene. Likewise, if an individual with leukemia claims that benzene exposure was the cause, it becomes necessary to evaluate the history of that individual’s exposure to benzene.4

Understanding exposure is essential to understanding whether the toxic properties of chemicals have been or will be expressed. Thus, claims of toxic tort or product liability generally require expert testimony not only in medicine and in the sciences of epidemiology and toxicology, but also testimony concerning the nature and magnitude of the exposures incurred by those alleging harm. Similarly, litigation involving the regulation of chemicals said to pose excessive risks to health also requires litigants to present evidence regarding exposure. The need to understand exposure is a central topic in the reference guides in this publication on epidemiology and toxicology. This reference guide provides a view of how the magnitude of exposure comes to be understood.5

1. See Michael D. Green et al., Reference Guide on Epidemiology, in this manual.

2. See Bernard D. Goldstein & Mary Sue Henifin, Reference Guide on Toxicology, in this manual.

3. See, e.g., Rhodes v. E.I. du Pont de Nemours & Co., 253 F.R.D. 365 (S.D. W. Va. 2008) (suit for medical monitoring costs because exposure to perfluoroctanoic acid in drinking water allegedly caused an increased risk of developing certain diseases in the future); In re Welding Fume Prods. Liab. Litig., 245 F.R.D. 279 (N.D. Ohio 2007) (exposure to manganese fumes allegedly increased the risk of later developing brain damage).

4. See, e.g., Lambert v. B.P. Products North America, Inc., 2006 WL 924988 (S.D. Ill. 2006), 2006 U.S. Dist. LEXIS 16756 (plaintiff diagnosed with chronic lymphocytic leukemia was exposed to jet fuel allegedly containing excessive levels of benzene).

5. This chapter focuses on measuring exposure to toxic substances as a specific developing area of scientific investigation. This topic is distinct from the legal concept of “exposure,” which is an element of a claim in toxic tort litigation. The legal concept of exposure relies on the evolving scientific understanding of the manner and extent to which individuals come into contact with toxic substances. However, the legal concept also reflects substantive legal principles and interpretations that vary across jurisdictions. Compare Parker v. Mobil Oil Corp., 793 N.Y.S.2d 434 (2005) (requiring findings of specific levels of exposure to benzene by plaintiff who claimed that his leukemia was the result of his

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