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Environmental
health science distinguishes among chemical, physical, biological, and
social hazards to human health.
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Modern
Western-style development creates many products and wastes, some of
which create hazards to human health.
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Modern
Western-style development changes the environment in ways that are
neither sustainable nor equitable at a global scale.
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In
terms of their behavior in the environment, organic chemicals have
characteristic tendencies.
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Although
they make up only a small proportion of the atmosphere, certain
gases in the Earth’s
atmosphere have important functions.
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Water
circulates through the environment, as shown in Figure 2.3 in the
textbook. Important
parts of the hydrologic cycle take place underground and may be
unfamiliar to
some readers.
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Environmental
chemicals can enter the body, where they may be transformed, transported,
and ultimately removed from the body.
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The
quantitative relationship between the dose of a toxicant and its toxic
effect is usually
presented as a dose–response curve.
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The
chronic rodent bioassay is the cornerstone of toxicity testing in
animals.
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Given
that “the dose makes the poison,” it is important to measure or
estimate exposure
as accurately as possible. Modern science frames the assessment of
exposure in terms
of an exposure pathway.
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Ideally,
exposure is quantified inside the body. However, often this is not
practical, and a
measurement made in the environment is used as proxy.
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As
a practical matter, certain environmental media are most associated
with each of
the three major routes of exposure.
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Modern
science uses various techniques to measure or estimate exposure all
along the exposure
pathway.
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he
units typically used to quantify absorbed dose are milligrams of
toxicant per
kilogram of body weight per day, or mg/(kg 3 day).
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Epidemiologists
use three distinct measures—incidence, prevalence, and mortality
— to quantify a given disease in a population.
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Surveillance
epidemiologists typically use one of two measures to compare rates
of death and disease in different populations: the standardized rate
ratio or the standardized incidence
(or mortality) ratio.
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Several
distinct study designs are used in environmental epidemiology, depending
on the investigator’s purpose and the availability of data.
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Not
every statistical association represents a causal association.
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Community
participation in health research is often valuable.
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Risk
assessment is an applied science used to evaluate the public health
risk of environmental
hazards using information on exposure and toxicity.
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The
conceptual divide between non-cancer and cancer health effects that
appeared in
toxicology is carried through in the risk assessment of chemicals.
Therefore, the four
major steps in risk assessment are parallel, but not the same,
in risk assessment for non-cancer and
cancer effects of chemicals.
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When
the risk assessment approach is applied to a site, the same four steps
are followed, but
they play out differently in this context. This is because most sites
are contaminated by
multiple chemicals and because each contaminated site offers a
different set of opportunities
for exposure (see Table 2.6).
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In
environmental health, risk management consists of actions taken to
control or
reduce environmental health risks.
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Many
risk management actions are not as straightforward as setting a
drinking water
standard.
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The
general public’s perception of risk has been called “hazard plus
outrage.”
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Communication
between epidemiologists and research subjects has expanded well
beyond informed consent.
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The
consensus conference, though rarely used in the United States, is a
sophisticated form
of risk communication.
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The
precautionary principle is an alternative to the mindset of the risk
assessment – risk
management paradigm.
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Implementing
a precautionary approach in the United States would represent a
major shift from the risk assessment–risk management paradigm.
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Using
a structured process, it is possible to tap the collective knowledge
and judgment
of the lay public in the development of scientific knowledge.
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Like
a risk assessment, the health impact assessment is a structured
process to evaluate
public health impacts; unlike risk assessment, it looks forward rather
than backward in
time.
