Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
requirements for operating theatres or isolation rooms of infectious
patients are designed to dilute potential contaminants and pathogens.
On a larger scale, substitution of cleaner fuels (e.g., reformulated
or unleaded gasoline, cleaner coal, low-sulfur oil, natural gas)
radiation of food or ozonation of drinking-water are examples of risk
mitigation interventions based on the assumption that contaminant
reductions experienced in the environmental media will result in a
corresponding reduction in actual exposures and hence risk. It is
essential, then, to understand the efficacy of mitigation strategies
with respect to their effect on human exposures.
The combined use of total exposure assessment for air,
receptor-source modelling and economic principles can assist
environmental policy and regulation in developing risk mitigation
strategies. The hybridization of these well-developed models can be
used to assist in the identification of priority sources to target
regulatory programmes, and in the development of cost-effective
strategies for air pollution control to bring about the greatest and
earliest reduction in pollutant exposures.
Epidemiological information about the health effects of
relatively low levels of air pollutants now raises controversial
policy issues for risk management. On the one hand, the economic
consequences of these health effects may be substantial; on the other
hand, for some pollutants, control measures may become very expensive.
For pollutants such as VOCs, for example, exposure monitoring rather
than ambient air monitoring may lead to more rapid and cost-effective
risk reduction policies.
Developed countries have experimented with regulatory reforms
that include emission trading. Basically, the concept calls for
emission reduction at one source to be credited to the emission levels
at another source. These trading schemes are based on the assumption
that equal mass emission reduction of a pollutant would result in
equal health or ecological benefits. Thinking in terms of total
exposure assessment reorients the relative importance of sources and
their impacts on different populations. Accordingly, control options
for reducing exposures can be broadened (Smith, 1995).
2.5 Human exposure information in status and trend analysis
Evaluating the current status of exposures and doses in the
context of historical trends is an important tool for both risk
assessment and risk management. In many cases it requires collecting
exposure data over a relatively long period of time (e.g., 5-20
years). This can only be done through an exposure assessment study and
often when the contaminant has a long residence time in the
environment or biological tissue. If concentrations of a contaminant
exhibit high variability in environmental media, the study may require
relatively large sample sizes, the use of probability samples and/or
extensive follow-up to observe trends. Data on status and trends can
be invaluable for identifying new or emerging problems, recognizing
the relative importance of emission sources and exposure pathways,
assessing the effectiveness of pollution controls, distinguishing
opportunities for epidemiological research and predicting future
changes in exposures and effects (Goldman et al., 1992; Sexton et al.,
1992).
Exposure studies may be conducted to document the status and
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