Environmental Engineering Reference
In-Depth Information
that produce endotoxins. Endotoxins vary with species, with a greater vari-
ation in the structure of the polysaccharide and less with the lipid.
Endotoxin levels in air and other media are determined by bioassay
techniques using
(horseshoe crab) amebocyte lysate (LAL), which
clots or increases in turbidity on exposure to endotoxin. Endotoxin expo-
sures have been reported to be high in airborne dusts associated with cotton
processing and hog and poultry confinement operations. High concentra-
tions have also been reported for metal-cutting fluid mists, wastewater
treatment mists, and mists associated with the processing of fiberglass insu-
lation. Highest concentrations in these occupational environments range
from 100 to 16,000 endotoxin units per cubic meter (EU/m
Limulus
). Outdoor
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endotoxin levels are reported to be <2 EU/m
. Endotoxin levels ranging
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from 100 to 408 EU/m
have been reported in problem office buildings in
the Netherlands. Though the source is unknown, it is suspected that ele-
vated endotoxin levels are associated with cool-mist humidifiers used to
climate-control mechanically ventilated buildings in European countries.
Though modular and central humidifiers are used by millions of homeown-
ers and residential tenants, cool-mist humidifiers are not used in mechan-
ically ventilated buildings in North America. Exposure to high endotoxin
levels is reported to be the probable cause of humidifier fever, an illness
syndrome somewhat similar to hypersensitivity pneumonitis (but without
progressive lung damage). Outbreaks of humidifier fever are commonly
reported in northern European countries.
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2.
Microbial VOCs
A variety of microbial volatile organic compounds (MVOCs) are produced
during bacterial growth. They are associated with the sour smell of wash
waters; the septic odor of sewage; the smell of human wastes and other
dungs; the putrid odors of animal and plant decay; the earthy odor of soil,
human body odor; etc. Volatile emissions from bacterial growth may include
inorganic gases such as methane, hydrogen sulfide, and ammonia from
anaerobic decomposition; amines such as cadaverine associated with the
decay of animal flesh; and a variety of alcohols and ketones. Geosmin, an
MVOC associated with some fungi, is the major odoriferous MVOC pro-
duced by the “higher bacteria,” the actinomycetes. It is responsible for the
characteristic odor of soil.
3.
Indoor exposures
Relatively few studies have been conducted to assess airborne bacterial levels
in indoor spaces and to identify major genera and species present. Most
assessments of airborne bacterial concentrations have been conducted using
culturable/viable sampling procedures. Typically, concentrations vary from
several hundred to several thousand colony-forming units per cubic meter
(CFU/m
). Under building closure conditions, humans themselves appear
to be the major source of airborne bacteria. Gram-positive cocci such as
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