General principles of exposure assessments

Exposure is defined as the contact (at visible external boundaries) of an individual with a pollutant for specific durations of time (IPCS, 2004a). For exposure to occur, an individual must be present and must come in contact with a contaminated medium. Exposure usually results in absorbed dose when chemicals enter the body. Exposure is described in terms of the intensity, frequency, and 

Children s exposure to environmental contaminants is a complex process that can occur as a result of release of pollutants from many sources that can reach the child through a number of different routes and pathways (Cohen Hubal et al., 2000b). Aggregate 

Cumulative risk assessments evaluate the health risk for aggregate exposures accumulated over time and for multiple contaminants or stressors. In some contexts (e.g. USEPA pesticide risk assessments), cumulative refers specifically to combined exposures to chemicals that share a common mechanism of toxicity (see http // www.epa.gov/oppsrrdl/cumulative/). Populations may be defined by their location relative to sources, their activities and customs, and their susceptibility to exposures. In this context, populations can include different ethnic groups, different communities, or different age groups. Cumulative risk is a very important concept in understanding environmental health risks to children in different settings, particularly in underdeveloped countries where children may be facing multiple stressors. 

Route of exposure is defined as the portal of entry to the body. Pathway is defined as the course that the contaminant takes from its source to the exposure medium, and then to the portal of entry. For a given source, exposure media and exposure routes can define the pathways. Depending upon the life stage of the child, exposure media can include amniotic fluid, breast milk, air, water, soil/dust/ sediments, food, and objects/surfaces. Exposure routes include transplacental transfer, inhalation, ingestion, dermal absorption, and indirect (non-dietary) ingestion. 

Exposure media will also change with life stage. For example, the fetus will be exposed via amniotic fluid, the infant to breast milk, the teething child to many objects (both intended and unintended) 

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The exposure assessment characterizes the pathways, magnitude, frequency, and duration of human exposures from various sources. Chapter 5 provides an overview of these components and addresses the principles of exposure assessment in children. General principles of exposure assessment have been reviewed in a number of publications (USEPA, 1992a, 2005a IPCS, 1999a, 2000 Needham et al., 2005). This chapter will focus on the considerations that are important when applying the exposure data to a children s health risk assessment (see Box 2). 

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