Environmental Engineering Reference
In-Depth Information
spores and structures. Such differences are typically the case when studies
are conducted in the winter and under closed building conditions. There is
only limited intrusion of outdoor airborne mold into indoor spaces when a
building is under closure conditions. Mold taxa commonly reported in out-
door air samples include the phylloplane fungi (grown on the surface of
leaves):
Cladosporium, Alternaria, Epicoccum,
and
Aureobasidium
;
Dresclera
,
Fusarium
, and a number of species of basidiomycetes; and plant pathogens
such as
Botrytis, Helminthosporium
, and
Ustilago
. Less commonly the mold
taxa
are reported. Dozens of mold types are
present in samples collected outdoors; however, individual samples tend to
be dominated by a relatively few taxa, with
Aspergillus
and
Penicillium
Cladosporium
and basidiomycetes
being most abundant.
Outdoor mold concentrations as determined by culturable/viable sam-
pling methods vary from nondetectable (under cold, snow-covered condi-
tions) to tens of thousands of colony-forming units/cubic meter (CFU/m
).
High concentrations are reported during the autumn when decomposing
plant material is abundant and grain harvesting is taking place. Under mod-
erate weather conditions, outdoor culturable/viable mold concentrations are
typically in the range of hundreds to thousands of CFUs/m
3
. With the
exception of the winter season, outdoor mold levels are almost always higher
than those measured indoors under closure conditions.
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B.
Indoor prevalence
Indoor mold taxa and their concentrations are also quite variable. This is
due to factors such as the intrusion of outdoor mold spora, the presence or
absence of sources of mold infestation, the nature of mold infestation and
its location, and building type. In the latter case, residential buildings typi-
cally have both higher concentrations and a greater range of taxa present
than mechanically ventilated buildings. While few differences in both mold
taxa present and airborne concentrations are seen between indoor and out-
door samples when significant intrusion of outdoor mold spora occurs,
significant differences between indoor and outdoor samples may be
observed under closure conditions.
Mold taxa commonly reported and found in the highest concentrations
indoors are, in declining order:
Cladosporium, Penicillium,
and
Aspergillus.
Less commonly reported and in fewer numbers are the taxa:
Alternaria,
Fusarium, Epicoccum,
Mucor, Rhizopus, Aureobasidium,
Chaetomium, Acremonium, Monilia, Pithomyces, Paecilomyces, Trichoderma, Scop-
ulariopsus,
yeasts, basidiomycetes,
and rarely,
Stachybotrys
. Abundance, however, varies with the
nature and degree of infestation.
Highest airborne mold concentrations are reported in buildings where
significant mold infestation has occurred, most notably houses that have
experienced severe flood damage. Mold concentrations in flood-damaged
houses may be in the tens of thousands of CFUs/m
. In buildings experi-
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