Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Immunochemical assays for fungal allergens are available for only
a few fungi, primarily because fungal allergens are poorly
characterized and purified. Alternative indicators of exposure to
fungi, to be measured in (airborne) dust, may also be considered. For
example, one can assess the levels of cell wall components such as
ß-1,3-glucan (Rylander et al., 1992), or ergosterol, a membrane
steroid (Horner et al., 1994), or extracellular polysaccharides (EPS)
(Kamphuis et al., 1991). Immunochemical assays (ELISA) are presently
being developed to measure these components in (airborne) dust.
However, in one study by Miller et al. (1988), ergosterol in house
dust correlated with CFU/m 3 in the air and Saraf et al. (1997) have
shown ergosterolin in house dust correlated with fungal CFU/g in the
dust samples. In addition, Abramson et al. (1996) showed an
association between ergosterol and atopy in adults.
9.4.3.1 Total counts of viable and non-viable fungal particles
Total counts of fungal particles can be obtained by counting with
a light microscope. If more detail is required, the samples can also
be viewed with a scanning electron microscope (SEM) or a direct
epifluorescence microscope. These techniques cannot be recommended as
giving a good assessment of the composition of air spora because only
fungi with distinctive spores can be identified. It is often difficult
to identify the fungal spores to species or even genus. As indicated
above, filter methods may be used not only to give total counts (e.g.,
by direct epifluorescence microscopy), but also to obtain counts of
viable fungal particles by plating washings from the filter.
Furthermore, filter samples may be analysed for mycotoxins, EPS and
glucans or tested for toxicity. The same applies for samples of
settled dust.
9.4.4 General considerations for fungi
Since fungi vary so widely it is difficult to generalize about
the presence of fungi in outdoor and indoor air. In temperate
climates, outdoor spore counts are highest during and just following
the growing season. Tropical climates show less variation by season.
Garrett's (1996) doctoral thesis provides a useful comparison of
viable mould spores from studies conducted in different climates.
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