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"Toxic substances have the capacity to disrupt the development of all of the body's organ systems. The nature and severity of that disruption depend upon the type of substance, the level and duration of exposure, and most important, on the timing during the developmental process...
"It is generally assumed that the adverse impact of toxic substances on the developing architecture of the brain is an all-or-none phenomenon. In fact, neurotoxins can produce a range of outcomes, from mild to severe impairment, which often lead to confusing conclusions about the linkage between exposure to a specific substance and its consequences...
"It is generally assumed that the determination of a dangerous level of exposure to a potentially neurotoxic substance is a straightforward scientific question. In fact, this can present a complicated challenge because the developing brain of a young child is typically more susceptible to damage than the mature brain of an adult, and the immature nervous system of an embryo or fetus is even more vulnerable to toxic exposures than is that of an infant. Therefore, there is no credible way to determine a safe level of exposure to a potentially toxic substance without explicit research that differentiates its impact on adults from the greater likelihood of its adverse influences on the developing brain during pregnancy and early childhood...
"The importance of determining which substances are safe and specifying thresholds of exposure for those that are dangerous is not yet incorporated into public policy. These tasks are complicated by the fact that policy initiatives in this area are driven largely by popular beliefs, which are influenced primarily by advocacy groups and media reports that often are not updated as new science becomes available...
"The establishment of safe levels of exposure to toxic substances should be based on scientific data that recognizes the critical link between vulnerability and age. In view of the well-established scientific fact that embryonic, fetal, and early childhood brain development is considerably more susceptible to damage from toxic substances than the mature brain of an adult, the establishment of thresholds for toxic exposures should focus primarily on the best data available for the youngest children."
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