Bioaerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 317

emissions are generally 50-200 nm in diameter and are the most abundant ambient particles by
number. The association between trafic-related particle exposure and persistent wheezing at 36
months of age can be modiied by exposure to endotoxin, a inding that supports prior toxicological
studies demonstrating a synergistic production of reactive oxygen species after coexposure to diesel
exhaust particles and endotoxin. 331

12.6 ENVIRONMENTAL MEASUREMENT AND ANALYTICAL TECHNIQUES

12.6.1 e xPosure a ssessMent
Assessment of exposure to environmental agents in indoor and outdoor air plays a central role
in epidemiological studies seeking to characterize population risks, screening studies aimed at
identifying individuals at risk, and interventions designed to reduce risk. 77 However, the assess-
ment of bioaerosol exposures presents challenges distinct from those for inorganic aerosols and
chemical agents. Pathogenic microorganisms may be hazardous at extremely low concentrations
while other organisms may become important health hazards only at orders of magnitude higher
concentrations.
Even when air samples are collected to determine bioaerosol concentrations, exposure typically
is estimated from a readily measured surrogate of an active agent, for example, fungal spores,
ergosterol, glucans, or mannitol to represent fungal allergens or toxins, whole pollen grains for plant
allergens, guanine for house dust mite allergens, or CFUs of Gram-negative bacteria for endotoxin.
Certain bacteria and fungi that have been observed in moisture-damaged buildings have been sug-
gested as “indicator species.” 332 Other researchers have used the indoor presence of hydrophilic
(water-loving) fungi as an indicator of water damage and as possible markers of increased risk of
building-related respiratory diseases. 333

12.6.2 b ioaerosol M easureMent
Bioaerosols are collected for a wide variety of purposes, for example, to measure inhalation expo-
sure, characterize indoor and outdoor environments, identify emissions from work activities, and
evaluate the effectiveness of control methods. Table 12.2 lists some commercially available bio-
aerosol instruments. For reviews of bioaerosol samplers and study design, see Cox and Wathes, 334
AIHA, 205,335 ACGIH, 201 Hurst, 336 and Muilenberg. 337

12.6.3 b ioaerosol s aMPlers
Most bioaerosol samplers are based on active collection using a pre-determined air low. Because
active air sampling may not be feasible in population-based studies, some investigators have substi-
tuted breathing-zone, dust sampling platforms for passive, long-term collection of settled dust. 338,339
Another alternative to active air sampling is a specially designed aerosolization chamber that
collects particles from contaminated surfaces released by air currents and vibration, that is, the
Fungal-Spore Source Strength Tester (FSSST) 340 and the Particle-Field and Laboratory Emission
Cell (P-FLEC). 341

12.6.3.1 Inertial Sampling
Impactors operate on the principle of drawing air through a nozzle and forcing the jet to turn
sharply after exiting the inlet. Particles larger than the d 50 cutoff diameter are collected with at least
50% eficiency. Many single- and multiple-jet impactors have been developed to collect bioaero-
sols (single-stage and cascade impactors, Table 12.2). A positive-hole correction may be applied to
the colony counts obtained with multiple-hole agar impactors to account for coincidental impac-
tion at high particle concentrations. 342,343 The impaction stage typically is removable to allow easy