Academic journal article Defense Counsel Journal

Role of Toxicology in Toxic Tort Litigation: Establishing Causation

Academic journal article Defense Counsel Journal

Role of Toxicology in Toxic Tort Litigation: Establishing Causation

Article excerpt

TOXICOLOGISTS research the nature of any adverse health effects produced by a chemical and assess the probability of occurrence of these adverse effects. In applying their science to toxic torts, toxicologists establish the known effects of the chemical in human beings and determine whether the alleged dose experienced by plaintiffs was sufficient to have caused any of their alleged diseases. Called "causation analysis," this process utilizes a specific methodology to establish to a scientific degree of certainty whether plaintiffs' claims are valid.

Possibly the first effort to formalize this objective methodology occurred more than a century ago with the development of the Henle-Koch postulates for establishing the causes of infectious diseases. Sir Bradford Hill later defined a similar methodology for determining whether a particular chemical found in the workplace should be considered a human carcinogen. Now there are at least 10 criteria proposed as the basis of the scientific method for determining whether a chemical in fact does cause a specific disease in human beings.(1)

These criteria include:

1. The strength of the human association,

2. The consistency of the human association,

3. The specificity of the human association,

4. Temporal relationships,

5. Dose-response relationships,

6. Biological plausibility,

7. Experimental evidence in animals,

8. Structure activity analogy,

9. Confounding disease or risk factors, and

10. The coherence and weight of the evidence.

Regulatory agencies are recognizing the importance of adhering to an established scientific methodology to determine risks. In its 1992 draft guidelines for carcinogen risk assessment, the Environmental Protection Agency cites seven criteria(2) adapted from Rothman(3) as those it recognizes as the scientific method that should be used to determine whether a chemical is a human carcinogen. These are:

1. Temporal relationship.

This is the single absolute requirement. It does not prove causality itself, but it must be present if causality is to be considered. The disease must occur within a biologically reasonable time frame after the initial exposure. The initial period of exposure to the agent is the accepted starting point in most epidemiologic studies.

2. Consistency.

Associations are observed in several independent studies of a similar exposure in different populations. This criterion also applies if the association occurs consistently for different subgroups in the same study.

3. Magnitude of the association. A causal

relationship is more credible when the risk estimate is large and precise (narrow confidence intervals).

4. Biological gradient. The risk ratio is

correlated positively with increasing exposure or dose. A strong dose-response relationship across several categories of exposure, latency and duration is supportive, although not conclusive, for causality, given that confounding is unlikely to be correlated with exposure. The absence of a dose-response relationship, however, should not be construed by itself as a lack of a causal relationship.

5. Specificity of the association. The

likelihood of a causal interpretation is increased if a single exposure produces a unique effect (one or more cancers also found in other studies) or if a given effect has a unique exposure.

6. Biological plausibility. The association

makes sense in terms of biological knowledge. Information from animal toxicology, pharmacokinetics, structure-activity relationship analysis and short-term studies of the agent's influence on events in the carcinogenic process are considered.

7. Coherence. The cause and effect

interpretation is in logical agreement with what is known about the natural history and biology of the disease--that is, the entire body of knowledge about the agent. …

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