described three mechanisms by
which ambient odors might elicit health symptoms: (1) exposure
to odorous compounds elicits a response in the trigeminal nerve
system referred to as an irritation effect (irritation causes the
health symptoms, whereas odor is the exposure marker); (2) at
nonirritant concentrations exposure elicits an innate, learned aversion;
(3) copollutants (such as endotoxin) elicit a health symptom
response. They note that objective bio-markers of health symptoms
are needed, to determine if and when health complaints constitute
health effects. For these reasons, measurements of volatile
compounds, dust (particulates which can absorb and re-volatilize
compounds), odor, and irritation are needed along with measurements
of bioaerosols and endotoxin to discern the contribution
of each and the health effect. An additional factor that complicates
the situation is that odorous compounds, even when individually
present below their irritant threshold concentrations, can when
present in mixtures collectively exceed an irritant threshold concentration
and thus elicit a response in a sensitive receptor