Bioaerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 308

exposure in early life may protect against allergy development and new onset asthma (Section
12.2.4), and it has even been suggested that endotoxin may reverse pre-existing atopic sensitization
and related diseases. 9 Thus, the role of nonoccupational endotoxin exposure in allergy and asthma
development is currently unclear.
12.3.2.2 Fungal Spores and Hyphal Fragments
Human challenge studies of school personnel with BRI have shown no observed effect levels
(NOEL) of 4 × 10 3 and 8 × 10 3 spores/m 3 for Trichoderma harzianum and Penicillium chrysoge-
num , respectively. 195 For Alternaria alternata and Penicillium species, lowest observed effect levels
(LOEL) for airway obstruction in patients with mild allergic asthma were found to be 1 × 10 4 and
2 × 10 4 spores/m 3 , respectively (the applied doses were calculated to equal an 8 h exposure). 196 In
various worker populations (e.g., wood workers, waste handlers, and farmers), a variety of respira-
tory effects such as symptoms, lung function changes, and increased inlammatory airway markers
have been observed at concentrations >10 5 spores/m 3 . Experimental studies have further shown that
the inlammatory effects do not depend on fungal (actinomycete) viability, 197 although there may be
differences in fungal allergenicity. 198
For indoor air quality assessments, concentrations measured in test environments are typi-
cally compared to baseline data from reference areas or to data reported in the literature. 199 The
extremes (∼95th percentiles) of Finnish data distributions of indoor, culturable bacteria and fungi
(5000 CFU/m 3 and 500 CFU/m 3 , respectively) have been recommended as indicators of the presence
of abnormal indoor sources or insuficient ventilation (but not health risk) in urban and suburban
residences in a subarctic climate. 164 The Finnish National Guidelines of Indoor Air Quality incor-
porated these values for the interpretation of bioaerosol sampling results. 200 However, the general
consensus is that it is not possible to set health-based, numeric concentration limits for bacteria or
fungi in indoor and occupational environments. 79,201-207
In addition to spores, fungi also release even smaller fragments. 208 These are derived from bro-
ken or fractured spores and hyphae and can be categorized into submicrometer particles (<1 μm) or
larger fungal fragments (>1 μm). Like spores, hyphal fragments are known to contain allergens 209
and mycotoxins. 210 Therefore, both spores and fungal fragments may play a role in mold-related
adverse health effects, and indoor exposures to fungal fragments may be at least as important as
fungal spores (Section 12.4.1.3).
12.3.2.3 Fungal (1 → 3)- β - d -Glucans
(1 → 3)-β-d-glucans are nonallergenic water-insoluble structural cell wall components of most
fungi, some bacteria, most higher plants, and many lower plants. They consist of glucose polymers
with variable molecular weight and degree of branching. Methods to analyze (1 → 3)-β-d-glucans
in environmental samples have not been standardized; therefore, measurements are not comparable
across studies making dose estimations dificult.
Elevated levels of (1 → 3)-β-d-glucans have been demonstrated in buildings with mold problems
and several occupational settings including sawmills, the paper industry, waste handling and recy-
cling, and farming. 211 In Sweden and Switzerland, glucan concentrations in airborne dust vigorously
generated from settled dust from buildings with fungal problems ranged from ∼10 to >100 ng/m 3
using a Limulus Amebocyte Lysate (LAL) assay (Section 12.6.4.3). 212 Air concentrations in build-
ings with no obvious fungal problems were close to 1 ng/m 3 . In the Netherlands and Germany, mean
(1 → 3)-β-d-glucans concentrations in house dust determined with a speciic enzyme immunoassay
(Section 12.6.4.4) were highly comparable, with concentrations of ∼1-2 mg/g dust and 0.5-1 mg/m 2 ,
respectively. 213-217
One study suggested that glucan exposure was associated with an increased risk of atopy, similar
to that observed in some animal studies, but this inding was not conirmed in a smaller study, 211 and
some studies even have shown a protective effect on respiratory health outcomes. 12,118 The evidence
with regard to the potential effects of glucan on airway inlammation is mixed. In vitro studies have