Heath Risk Science - Use of risk assessment for exposure
guidelines
Many goods and services on which the public relies either use or
produce chemical substances. Under certain conditions, exposure to
some of these substances could be harmful to human health.
In order to assess the risks posed to human health by chemical substances,
scientists examine the types of health effects that a particular
substance may cause and the likelihood and
manner in which people could be exposed. Simply identifying a hazard
does not imply that there are risks to the population; rather, characterization
of risks requires that the relationship between
different levels of exposure and the possible occurrence of adverse
health effects is understood.
Characterizing exposure also permits understanding of by what routes,
and the extent to which, the public is exposed to chemical substances
(for example, through air, food, drinking water or household products).
Characterizing both the potential hazards to human health as well
as human exposure, also enables identification of potential vulnerable subpopulations (eg.,
young children or infants) that might be either more highly exposed
or more susceptible to the effects of certain chemical substances.
To characterize risk, estimated exposure of the population (or subgroups)
is compared to the levels of a substance that may cause harmful effects. This
information is often derived from epidemiological studies of human
populations exposed in the past or toxicological studies in experimental
animals. Direct comparisons between levels which induce effects and
estimated exposure result in Margins of Exposure (MOE).
Alternatively, exposure is compared to a Tolerable or
Acceptable Daily Intake which is the level to which
it is believed that the public may be exposed daily without adverse
effect.
In interpreting Margins of Exposure or developing Tolerable or Acceptable
Daily Intakes, potential variations between animals and humans and
within the human population (e.g., susceptible populations) are taken
into account. For tolerable daily intakes for example, levels which
induce adverse effects are divided by uncertainty factors which
protect for these differences between animals and humans and within
the human population (e.g., for susceptible populations).
Guidelines or standards for chemicals in
various media such as drinking water and air and products to which
the public is exposed are often developed on the basis of these tolerable
or acceptable daily intakes. Media are then monitored to ensure
that levels do not exceed these values and where they do, risk
management action taken to reduce levels.
Estimates and margins of exposure and tolerable or acceptable daily
intakes are generally based on a thorough review of the scientific
literature involving input from highly qualified specialists through
a formal process of engagement. Since there are sometimes gaps in
knowledge, the relative uncertainty of and degree of confidence in
the underlying databases on exposure and effects are characterized
to provide information relevant to decision making on additional
research and the management of risk.
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