Children are more susceptible than adults to chemical exposures, and their exposure varies, depending on their physical location, breathing zones, oxygen consumption, types and amount of food and water consumed, and normal behavioral development. Specific exposures over time depend on developmental stage and the mechanism by which the agent produces its effect (EPA exposure guidelines, 2003). Estimates of chemical exposure are often retrospective, because it is difficult and costly to monitor exposures as they occur. Even if the total duration or dose of exposure is the same for two children, different patterns and timing of exposure may result in different health effects. For example, ingestion of nitrates in well water may reduce hemoglobin to methemoglobin, which is incapable of transporting oxygen (Lukens, 1987). However, if the nitrates are ingested at a slow enough rate for enzymes to change methemoglobin back to hemoglobin, no deleterious health effects occur. This is an example of a threshold effect; the health effect will not occur until the dose from the exposure reaches a particular level in the body.
Physical location. The newborn is usually held by or near the mother, or spends extended periods in a single environment (e.g., a crib), rather than several different environments. Infants and toddlers who are frequently placed on the floor, carpet, grass, or a blanket are exposed to chemicals associated with these surfaces, such as formaldehyde and volatile organic chemicals from synthetic carpet (Bernstein, 1984), pesticide residues from flea bombs (Fenske et al., 1990), dust mites, pet dander, and detergent residues. Preambulatory children also may experience sustained exposure to noxious agents because they cannot remove themselves from their environment. For example, the premobile infant must be protected from sunburn by the caregiver (Lowe et al., 2002).
Breathing zones. The breathing zone for a child, which varies based on height and mobility, is typically much lower than that of an adult. Chemicals that are heavier than air, such as methyl mercury, large particulates (Leaderer, 1990), and radon (Blot et al., 1990) accumulate in lower breathing zones. The presence of mercury in latex house paint in a child’s breathing zone results in acrodynia, a hypersensitivity reaction to mercury, also known as pink disease, and prompted legislation mandating the removal of mercury from house paint (Centers for Disease Control and Prevention, 1990b).
ral toxins as Pfiesteria toxins, organic chemicals including pesticides, PCBs, trichloroethylene, and chlorination by-products, such inorganic ions as nitrates, and such radionuclides as radon. Systems affected by these contaminants include the central nervous system, the gastrointestinal system, and the hematological system. Many of these chemicals are also carcinogens. Children have been found to be at higher relative risk of gastrointestinal illness from contaminated water (Wade et al., 2003). In addition, children are both more highly exposed and more susceptible to the contaminants found in water. For example, lead in drinking