Consideration of Infants and Children in Risk Assessment
Age-related physiological and behavioral differences can also affect the degree of exposure to environmental chemicals. The following sections discuss age-related toxicodynamic and toxicokinetic differences and approaches by the United States Environmental Protection Agency (USEPA) and California EPA’s (Cal/EPA) Office of Environmental Health Hazard Assessment (OEHHA) to address infants and children in risk assessment. 4.1.1 Toxicodynamics: Changing Targets of Toxicity
Development involves a complex series of events that change the structure and function of developing organs. For example, Rice and Barone  describe critical stages of development in the central nervous system (CNS) during fetal development and childhood involving rapid cell proliferation, migration, and differentiation. These developmental processes must be exquisitely coordinated both in time and space for complete brain development. Chemical-induced disruption to any of these processes may be irreversible and result in adverse structural or functional neurological deficits in the developing child. Coordinated developmental processes occur in every organ and organ system. Exposure to chemicals that disrupt developmental processes can potentially disrupt the structure and function of any organ system. Since development continues into young adulthood, exposures during childhood should be viewed as having potential to cause developmental toxicity. For example, structural maturation of the CNS continues through adolescence, involving both cell proliferation and synaptic pruning (loss of selected neurons) . Disruption of these processes could lead to functional alterations in higher level functions of the brain. Similarly, the peripubertal period presents windows of susceptibility for the reproductive organs and mammary glands, which are experiencing rapid growth and concomitant rapid cell proliferation and differentiation.