Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Few published data are available on the validity of the
measurement of culturable fungi in settled dust as estimate of
exposure. The results, both quantitatively and qualitatively, depend
on the method of inoculation of the dust and on the culture medium
used (Verhoeff et al., 1994a). The reproducibility of duplicate
analyses in terms of CFU/g dust is acceptable, but in terms of species
isolated only moderate. However, as is the case for air sampling, a
single dust sample is a poor estimate of exposure to fungi over time
(Verhoeff et al., 1994a).
9.4.3 Available methods of analysis for fungi in air
Air samples obtained with sampling devices collecting total
fungal particles can be analysed by direct examination to obtain total
counts of fungal particles. Samples collected on culture media have to
be incubated to obtain counts of viable fungal particles. Dust can be
plated either directly on to a culture medium or suspended and diluted
prior to plating. Total counts of fungal particles in dust can also be
obtained by partitioning into an aqueous two-phase system followed by
epifluorescence microscopy (Strom et al., 1987).
Samples are incubated for at least 4 days; up to 7 days is the
typical time needed for spores to generate identifiable colonies. The
temperature at which samples are incubated affects the recovery of
culturable fungi. Since most environmental fungi grow well between
20°C and 30°C, the incubation temperature is generally 25°C (EC,
1993).
Sporulating colonies are identified by colour and texture, by the
naked eye or microscopically. Non-sporulating spores might be
transferred to different agar and exposed to different lighting in an
attempt to colonize them. Fungal genera are sometimes reported and
provide important insight into sources and possible health effects.
Common outdoor fungi are Cladosporium, Alternaria, Botrytis and
Epicoccum. Penicillium, Aspergillus and Stachybotrys can be found
in higher concentrations indoors. It is difficult to generalize and
there is considerable variability over time so it is important to
simultaneously collect outdoor samples. Fig. 28 shows the distribution
of viable mould spores collected inside and outside homes in Australia
(Garrett, 1996). Outdoor viable spore counts decrease in the winter
and so do the indoor levels for homes without substantial sources of
sporulating fungi.
http://www.inchem.org/documents/ehc/ehc/ehc214.htm
Page 162 of 284
6/1/2007