The new tapestry of risk assessment

Abstract

Neurotoxicology is entering a new phase in how it views and practices risk assessment. Perhaps more than any of the other disciplines that comprise the science of toxicology, it has been compelled to consider a daunting array of factors other than those directly coupled to chemical and dose, and the age and sex of the subject population. In epidemiological investigations, researchers are increasingly cognizant of the problems introduced by allegedly controlling for variables classified as confounders or covariates. In essence, they reason, the consequence is blurring or even concealing interactions of exposure with modifiers such as the individual's social ecology. Other researchers question the traditional practice of relying on values such as NOAELs when they are abstracted from a biological entity that in reality represents a multiplicity of intertwined systems. Although neurotoxicologists have come to recognize the complexities of assessing risk in all its dimensions, they still face the challenge of communicating this view to the health professions at large.

Figure 1

Rates of return to human capital investment initially setting investment to be equal across all ages (Cunha et al, 2005).

Figure 2

Academic and social benefits at school exit for CPC participants (Cunha et al, 2005).

Figure 3

Multiple Exposures/Multiple Effects Model. (from: Briggs, D. 2003. Making a difference: Indicators to improve children’s environmental health. Prepared for the World Health Organization. Geneva, Switzerland: WHO)

Figure 4

Phenomenology of TILT. Illness appears to develop in two stages: (1) Initiation, i.e., loss of prior, natural tolerance resulting from an acute or chronic exposure (pesticides, solvents, indoor air contaminants, etc.), followed by (2) triggering of symptoms by small quantities of previously tolerated chemicals (traffic exhaust, fragrances), foods, drugs, and food/drug combinations (alcohol, caffeine). The physician sees only the tip of the iceberg—the patient’s symptoms—and formulates a diagnosis based on them (e.g., asthma, chronic fatigue, migraine headaches). Masking hides the relationship between symptoms and triggers. The initial exposure event causing breakdown in tolerance may go unnoticed (©UTHSCSA 1996).

Figure 5

Representative dose-response curves as seen in two contexts: An experimental context (top) and a public health context (bottom). Ordinate represents percent.