Changes in Children's Exposure as a Function of Age and the Relevance of Age Definitions for Exposure and Health Risk Assessment

Kimberly M. Thompson, ScD

Disclosures
In This Article

Abstract and Introduction

Objective: The objective of this study was to review and synthesize the existing exposure information available to support the characterization and estimation of children's environmental health risks as a function of age.
Method: This includes a review of the existing peer-reviewed literature and reports from the US Environmental Protection Agency (EPA) up through January 1, 2003 for information about exposure data for American children with a focus on identifying the age categories used and data gaps that limit our ability to estimate children's risks from exposure to environmental hazards.
Results: On the basis of this synthesis, several key data gaps emerge that suggest some areas in which exposure assessors may want to focus attention, including current breast milk consumption by infants and breastfeeding information for children over age 1 year; children's food-handling practices and how these lead to exposure (eg, by eating with dirty hands or by eating food that has dropped onto a contaminated surface); fish-intake rates for young children and for children whose families include sport fishers or whose families rely on self-caught fish for sustenance; incidental and intentional soil intake by children; soil adherence for dermal exposure; relationships between various microactivities, macroactivities, and microenvironments where children spend time; and a correlation between exposure factors and growth (ie, how children's exposure behaviors change over time). In contrast, relatively good exposure information exists for characterizing children's growth and water ingestion, and at least some exposure information exists for the wide ranges of exposures of regulatory interest.
Conclusion: Given the currently available data, exposure assessors can estimate children's potential health risks from a number of different types of exposure, but longitudinal data are needed to reduce the significant uncertainties that arise from reliance on currently available data, and a number of dose-response challenges remain.

During the past decade, improving the lives of children has emerged as a priority on the National Agenda.[1] In the public and environmental health areas, this priority emerged prominently in President Clinton's Executive Order 13045, which required federal agencies to ensure that their "policies, programs, activities, and standards address disproportionate risks to children that result from environmental health risks or safety risks." Congress also established children's health as a priority in changes to statutory requirements in the 1996 Food Quality Protection Act (FQPA) and the Safe Drinking Water Act. For example, FQPA created a demand for estimating aggregate exposure (ie, the amount of exposure from multiple pathways for the same substance) and cumulative risk (ie, the risk from all substances that act with the same mechanism of toxicity over all of the multiple pathways in which they may act).

The focus on children's health raises many challenges for exposure and risk analysts. Childhood represents distinct phases of human life, and children possess unique characteristics that distinguish them from adults. From birth to adulthood, their physiology and behavior constantly change, making them a "moving target" for exposure and risk assessment. This leads to a number of key questions:

  • How should the age-related changes in children's behavior and physiology be considered when assessing children's exposure to environmental contaminants?

  • What is the most appropriate way to categorize the available data into age groups when assessing children's exposure?

  • Given the rapid change in modern society, how representative are data from previous studies for today's children?

  • What is the most appropriate way to estimate childhood exposure given the limitations in currently available exposure information?

  • What further research is needed to provide the data necessary for estimating children's exposure and what short-term and longer-term data could provide the missing information?

With current discussions about the possibility of a National Children's Study, a proposed multimillion dollar longitudinal study that may provide information about approximately 100,000 American children potentially followed for 21 years,[2] risk analysts must ask important questions about what data would be the most valuable for researchers to obtain given the inevitability of difficult choices related to sample collection and survey design in the context of limited resources (eg, financial, technological, and research subject willingness to participate if the study presents too large a burden). This article synthesizes the most current and relevant information available regarding children's anatomic and behavioral changes and how these affect assessments of exposure. This article provides the important context for discussions about the value of obtaining additional exposure-factor information for children.

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