Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
same assay (Schou et al., 1991). For immunochemical analysis, the dust
sample is extracted (e.g., in a buffered saline solution), and then
stored frozen until analysis.
The ELISA assays for Fel d I and Can f I were found to be highly
reproducible (Chapman et al., 1988; Schou et al., 1992). For the
Bla g I and Bla g II ELISA assays the intra- and interassay
variability were also found to be small (Pollart et al., 1991b).
9.3.4 Typical allergen concentrations
Cat and dog allergens have been reported more often than
allergens from other mammals. Homes with cats have dust levels of Fel
d I exceeding 10 µg/g, whereas homes without cats have typically less
than 1 µg/g. A provisional value of 8 µg/g of dust has been proposed
as indicating significant exposure. Cat antigen has been found in dust
samples collected in theatres, offices, aeroplanes, schools and homes
without a cat. Because of its small particle size, cat antigen can
stick to clothing and be transported to other locations. Dog allergens
have not been as extensively examined for non-residential sites.
Dybendal et al. (1989) has reported that dog allergen was present in
homes and schools where dogs were not kept.
9.4 Fungi
Fungi are a large and diverse class of microorganisms. They live
on organic nutrients and have no chlorophyll or internal organs. The
cells that make up fungal colonies contain complex carbohydrate
macromolecules. Fungi must produce spores or conidia for their
reproduction. Spores are usually 2-20 µm in size and oblong in shape.
In the appropriate setting, spores reproduce new organisms.
The two different approaches to assess the exposure to fungal
particles are air sampling and dust sampling. For completeness, other
approaches to "dust" sampling include lifting spores from a surface
with sticky tape or direct contact with culture agar. The most
commonly used approach is air sampling of culturable (viable) fungal
particles.
9.4.1 Air sampling for fungi
Several techniques have been described for volumetric sampling of
fungi in outdoor and indoor environments. Table 32 presents an
overview of the techniques most commonly used for the sampling of
fungal particles. Detailed information on the different sampling
devices can be found in ACGIH (1995). Some of the techniques give
total counts of all airborne particles, viable and non-viable, whereas
others only give counts of viable fungal particles (e.g., propagules
or colony forming units (CFU)). A few methods are discussed that
provide not only total counts, but also viable counts (e.g., filter
samplers). The sampling efficacy of a bioaerosol sampler is both a
physical and a biological problem. For air sampling of fungal
particles the following physical sampling principles may be
distinguished: impaction on to a solid or semi-solid surface (e.g., a
culture medium or an adhesive), centrifugal impaction, filtration and
liquid impingement.
Impaction on to a culture medium (e.g., for culturable fungi) is
the most widely used technique, particularly in non-industrial indoor
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