Risk assessment: the insidious nature of neurotoxicity and the aging brain.

Neurotoxicology is a fertile source of ambiguities. They complicate the conventional risk assessment process, whose current procedures and models were designed to accommodate a unitary endpoint and mechanism. All of these ambiguities are multiplied by their interaction with aging because many manifestations of neurotoxicity, such as impaired sensory acuity, mimic the natural course of aging. With aging as a model, modifications of the risk assessment paradigm have been designed. These modifications take the form of adaptations able to accommodate the unique properties of neurotoxicity. Properties such as progressive declines in function, the late impact of prenatal damage, multiple endpoints, variations in exposure pattern, reversibility, and population shifts in performance are explicitly recognized by these adaptations.