Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
characterizing and reducing exposures to non-smokers, in particular,
infants and young children. Epidemiological studies conducted over the
last 15 years indicate that ambient particulate matter is adversely
affecting human health at levels well below many of the established
standards. Exposure assessment along with toxicology and epidemiology
will be needed to answer many of the remaining unresolved issues about
ambient and indoor suspended particles.
Other studies summarized show how exposure assessment is
supportive of epidemiology and risk management. The reader should
recognize that Chapter 12 is not comprehensive but is intended to help
educate the research community and others about the application, use
and limitations of exposure assessment methodologies.
1. DEFINING EXPOSURE
1.1 Introduction
People are exposed to a variety of potentially harmful agents in
the air they breathe, the liquids they drink, the food they eat, the
surfaces they touch and the products they use. An important aspect of
public health protection is the prevention or reduction of exposures
to environmental agents that contribute, either directly or
indirectly, to increased rates of premature death, disease, discomfort
or disability. It is usually not possible, however, to measure the
effectiveness of mitigation strategies directly in terms of prevented
disease, reduced premature death, or avoided dysfunction. Instead,
measurement or estimation of actual human exposure, coupled with
appropriate assumptions about associated health effects or safety
limits (e.g., acceptable daily intake, tolerable daily intake), is the
standard method used for determining whether intervention is necessary
to protect and promote public health, which forms of intervention will
be most effective in meeting public health goals, and whether past
intervention efforts have been successful (Ott & Roberts, 1998).
The purpose of this chapter is to define the concept of exposure,
and the direct and indirect method of exposure assessment. A brief
discussion of exposure in the environmental health paradigm and its
relationship to dose is presented.
1.2 Defining exposure
Exposure is defined as contact over time and space between a
person and one or more biological, chemical or physical agents (US
NRC, 1991a). Exposure assessment is to identify and define the
exposures that occur, or are anticipated to occur, in human
populations (IPCS, 1993). This can be a complex endeavour requiring
analysis of many different aspects of the contact between people and
hazardous substances (see Table 1). Although exposure is a
well-established concept familiar to all environmental health
scientists, its meaning often varies depending on the context of the
discussion. It is important however, that exposure and related terms
be defined precisely. In the following sections, we describe and
define important exposure-related terms used in this document. The
definitions are consistent with the US EPA's Exposure Assessment
Guidelines and related WHO publications (WHO, 1987, 1996a; US EPA,
1992a; IPCS, 1994). It is important to recognize, however, that
terminology and definitions vary among organizations and nations.
Thus, the reader is advised to concentrate on the concepts, rather
than the specific terms, as they represent the crux of exposure
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