Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
others should be well thought out before the commencement of a settled
dust sampling effort.
8.5 Summary
Human contact with soil and settled dust can be an important
source of exposure to chemical contaminants, especially for children.
Although many sampling methods have been developed, no single approach
has been demonstrated to be superior to the others. As a consequence,
it is difficult to compare results from studies that utilize different
sampling methods. Important factors to consider when selecting a
sampling method include collection efficiency, differences in human
activity patterns, physical variability of soil and dust levels over
space and time, surface and substrate sampled, timing of sample
collection and analytical methods used to measure toxicants in the
laboratory.
9. MEASURING BIOLOGICAL HUMAN EXPOSURE AGENTS IN AIR AND DUST
9.1 Introduction
Microbiological organisms have long played an important role in
human ecology. Fungi are critical to the production of cheese and the
fermentation of beer, and in some cases are a direct source of
nourishment. In the first half of the 20th century, Penicillium
chrysogenum colonies were discovered to inhibit growth of other
organisms. Today pharmaceutical companies, among others, are exploring
fungal enzymes for a variety of reasons including new drugs,
non-chemical pesticides, biodegradation of waste and possible
catalysis of chemical reactions.
However, natural does not mean benign. Human exposures to
microorganisms have resulted in allergic, toxic and infectious
disease. As humans have modified the environment through cultivation,
landscaping and building structures, ecological balances have been
disturbed. The distribution of moisture and nutrients has been altered
to a point where it is quite common to encounter reservoirs of fungi,
bacteria and algae, and infestations of mites and cockroaches.
Through airborne dispersion, ingestion or direct contact, humans
confront components of microorganisms continuously. We may be affected
through an immune reaction requiring sensitization. Predisposed
individuals may not experience a reaction for some time after they
have been exposed. Once an individual is sensitized, a reaction such
as an asthmatic attack might be delayed hours following the exposure
event. However, there are many infectious diseases induced by fungi
and bacteria that require no period of sensitization before illness
develops. There is yet another route whereby microorganisms can evoke
irritation and health effects: some metabolites from moulds are
carcinogenic (e.g., aflatoxin B) or immunosuppressors; some cause
dermatoxic effects; others cause annoyance and irritation by the VOCs
they release.
Table 31 provides basic categories for the microorganisms of
primary interest and some possible sources. Assessing exposures to
microorganisms is very different in some aspects from assessing
exposures to physical or chemical agents. For virtually all
microorganisms, exposure-response or dose-response information is
currently limited. Nevertheless, exposures to allergens, fungal
spores, Legionella, and tuberculosis, among many others, are being
http://www.inchem.org/documents/ehc/ehc/ehc214.htm
Page 149 of 284
6/1/2007