A DEVELOPMENTAL APPROACH TO PEDIATRIC ENVIRONMENTAL HEALTH

As Kenneth Olden, PhD, Director of the National Institute of Environmental Health Sciences, has stated, "A little kid goes from a single cell to a laughing sociable, intelligent, friendly human being over a course of two years: that's dramatic" (personal communication, 1995). The primary task of infancy and childhood is growth and development. The elegance and delicacy of the development of a human from conception through adolescence affords particular windows of vulnerability to environmental hazards. If this development is hampered, the likelihood of a healthy adulthood is decreased dramatically. Many different kinds of insults have the potential to damage these natural processes, potentially leading to lifetime harm. It is often impossible to repair damages that occur in childhood. It is not just the degree and route of exposure to an environmental toxicant but also the timing of the exposure that affects the response. For instance, at a given dose, intrauterine exposure to lead or polychlorinated biphenyls (PCBs) seems to be more damaging than later life exposure. 18 Also, the type of defect resulting is highly dependent on the timing of the exposure. And yet, what is not known about the effects and potential effects of exposures still far outweighs what is known. This lack applies in regard to nervous, reproductive, immune, and other crucial systems and the state of knowledge for carcinogenic, endocrine, and other health effects. Children are different from adults in many ways. Because biochemical systems still are developing in the fetus and the child, their ability to detoxify and excrete toxins differs from adults. This difference is sometimes to their advantage, but more frequently children do not have the same capacity to excrete toxins as do adults, and thus they are more vulnerable to them. Moreover, organs in children are undergoing growth and differentiation. Both of these processes may be affected by xenobiotics. The result of exposure to xenobiotics may be different in children than in adults in the degree of severity of effect and the nature of the effect. Behavioral differences between adults and children and between children of different ages mean that opportunities for exposure to environmental toxicants also differ. Exposure differences are a result of locations where children spend time, the activities in which they indulge, their patterns of diet and respiration, their level of personal hygiene, and their patterns of exploration of the world around them. All of these are rooted primarily in their developmental stage and the consequences of their associated behaviors. Thus, in identifying how children may be exposed to a chemical or other environmental toxicant and the level of exposure, it becomes inadequate simply to extrapolate from adult exposure because children are not "little adults." This article provides a framework for the study of children's environmental health by examining how children's exposure and susceptibility to environmental toxicants vary with their developmental stage. It explores common sources of exposure to toxicants and considers routes of exposure, metabolism, sensitive target tissues, and health effects at several points in development (i.e., preconception, fetus, newborn, infant and toddler, preschool and school age, and adolescence) to consider aspects of children's environmental health longitudinally.