Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
actinomycetes at 55°C. After incubation the number of colonies is
counted and expressed as CFU/m 3 .
9.5.3.3 Endotoxins
Endotoxins are a group of lipopolysaccharide (LPS) molecules
making up the outer membrane of Gram-negative bacteria. Specific LPS
macromolecules that exist in the cells or as fragments of cell
structures are known to cause fever, malaise, respiratory distress and
a variety of biochemical changes in humans. Endotoxins are ubiquitous
in nature but occur in high concentrations in particular industrial
and agricultural settings. Cotton mills and industrial processes using
recirculating water, waste-water collectors, humidifiers and swine
barns are some locations where endotoxin contamination has been
associated with respiratory disease (Milton, 1995).
Airborne and settled dust samples can be examined for the
presence of endotoxins. The Limulus amoebocyte lysate (LAL) assay is
commonly used to quantify environmental endotoxin (Walters et al.,
1994; Douwes et al., 1995). The assessment of endotoxin exposure
depends strongly on sampling, extraction and storage procedures
(Douwes et al., 1995) and further validation studies are needed to
adopt standard methods for sampling and analysis. Variation in the LAL
reagent from lot to lot and between manufacturers may be a major cause
of variation in results within and between laboratories (Saraf et al.,
1997).
In airborne endotoxin, filter material and type of aerosol (e.g.,
cotton dust, machine oil or saline mist) will affect the binding of
endotoxin to the filter. Walters et al. (1994) showed that
polycarbonate capillary pore membrane filters were optimal. Any
conventional air sampler can be used with filter cassettes. Glass
impingers have been used as alternatives to filters. Fluids and bulk
samples can be collected directly if care is taken to ensure the use
of endotoxin-free glass or plastic ware with low binding affinity.
Samples should be analysed promptly and preferably not frozen.
Endotoxin (LPS) is removed by solubilizing in a buffer solution (after
Milton, 1992). Sonication might be necessary to dislodge particles.
Concentrations, as measured by the Limulus assay, are expressed as
standard endotoxin units (EUs) which are defined as the potency of
0.10 ng of a reference standard endotoxin (EC6, US Pharmacopoeia).
9.6 Pollen
Most people associate pollen with the common experience of hay
fever and seasonal allergic rhinitis. Although only 10% of flowering
plants shed wind-borne pollen, there are locations and times when the
ambient concentrations exceed 1000 pollen grains/m 3 . Pollen grains
generally are spheroidal or somewhat elongated and have a very durable
outer wall. Most airborne pollen is between 10 and 70 µm in diameter.
Larger pollen grains (>200 µm) are more likely to be transported by
insects. Weather conditions such as higher temperature and lower
relative humidity and wind promote pollen emissions (Ogden et al.,
1969; Hart et al., 1994; Burge, 1995). Plant lifecycle stage, daylight
and moisture affect the time and rate of shedding. Flowering of most
plants, trees and grasses is seasonal and therefore cyclic.
Although hay fever in association with plant pollen has been
known for 175 years, the association of natural pollen with airway
reactions and asthma has not been adequately studied. Most pollen
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