Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
impactor is determined by the flow rate, jet size and shape (e.g., the
distance between the jet and the impaction surface) (Pastuska, 1988;
Lehtimäki & Willeke, 1993). The air flow rate must be calibrated
carefully because correct size selection depends largely on precise
flow rates.
Filters are made either from fibre mats of glass, cellulose or
quartz or from synthetic membranes (e.g., Teflon). The selection of
appropriate filters depends on the pump, filter static pressure,
collection efficiency, extraction and analytical requirements, and the
potential for sampling artefacts. Filter mass is determined by
weighing the filter under controlled temperature and humidity
conditions before and after use following a conditioning period of at
least 24 h at those same conditions. The collected mass can be
extracted and analysed for chemical composition. The extraction and
analysis procedures used depend on the analytes of interest. A recent
summary of methods for extraction and analysis of components of
particulate matter may be found in Koutrakis & Sioutas (1996).
7.2.3 Semivolatile compounds
For airborne contaminants that are present in both the particle
and the vapour phase at typical environmental conditions, it is
necessary to use a combination of sampling methods. The most common
approach consists of an aerosol sampling inlet (with or without size
preselector) followed by a sorbent cartridge or tube. Examples of such
contaminants include airborne PAHs, pesticides, polychlorinated
biphenyls (PCBs), dioxins and furans. Semivolatile sampling systems
are commercially available for personal air monitoring. Extraction and
analysis of these samples are done separately for the particle and
vapour phase and then the results are combined to provide a total
concentration. An introduction to sampling and analysis methods for
VOCs in air may be found in Binkova et al. (1995), Wallace & Hites
(1996), Wallace et al. (1996) and Simonich & Hites (1997).
7.2.4 Reactive gas monitoring
Certain gases present in air may react with chemicals present in
particles. For example, sulfuric acid particles collected on filters
can be neutralized by the ammonia gas present in the sample or air
stream. The preferred sampling approach to avoid this is to use a
denuder to remove the reactive gas before it reaches the downstream
filter. In the case of sulfuric acid monitoring, a citric-acid-coated
denuder is used to remove the ammonia gas. Small denuder systems are
commercially available for personal monitors. Denuder technologies are
described in Lodge (1988) and Koutrakis & Sioutas (1996).
7.3 Water
The sampling and analysis of drinking-water characterizes the
extent to which this carrier medium represents a source of specific
chemical exposure. Contaminated drinking-water supplies contribute to
the human intake of numerous chemical contaminants, including heavy
metals, fertilizers, pesticides, aromatic hydrocarbons and
organohalogens, among others. In some cases, drinking-water may be the
primary source of human exposure. Chemical pollutants in water may
originate from one or more of a myriad of sources, as summarized in
Table 25. In the selection of measurement and sampling methods, it is
important to consider raw water sources, water treatment processes,
and distribution and service systems, all of which can either reduce
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