40 AIR POLLUTANT EFFECTS
which leads to lung cancer. The radioactivity attributable to
radon in the air is measured in picocuries per liter, which
correspond to two atoms decaying per liter per minute. The
concentration of the decay products is measured in “working
level units,” where 1 working level unit^ of decay products is
released from approximately 200 pCi/l of radon.
The only certain method of determining the presence of
radon is by testing, which should be performed whenever a
dwelling is brought or sold. The EPA has prepared the “Home
Buyer’s and Seller’s Guide to Radon,”^ which provides informa-
tion about what can be done to protect against this problem.BIOLOGICAL CONTAMINANTSThe New York Academy of Medicine issued a resolution in
1983 (Health Aspects of Indoor Air, New York Academy of
Medicine [1981] 57, No.10) expressing its concern about the
damage to health caused by the inhalation of biologic agents
that points out that “by far the most important substances in
indoor air that affect human health are infectious agents, pri-
marily viruses and bacteria in the form of aerosols or as part
of droplets or particles. These cause more than 60,000 deaths
and 250 million disabling illnesses in the United States each
year.”^ In addition to viruses and bacteria, the indoor air can be
contaminated with pollens, fungal sores, algae, amoebas, acti-
nomycetales, arthropod fragments, and droppings and dander
from humans and animals. The airborne transfer of disease can
involve pathogenic, toxicogenic, or allergenic agents via short-
range direct person-to-person transfer or long-range dispersion
throughout rooms sharing a common ventilation system. An
important preventive strategy is to isolate other rooms from
contamination by the air from rooms containing sources of
microbial pollution.
Secondary sources of biological contamination can be
established indoors by viable organisms that find friendly
environments and sources of nourishment in soils, plants,
and stagnant water. Pathogens, toxins, and allergens can be
brought indoors through air intakes and shoes, clothing, or
tools. The human body—mainly from the nose and mouth
but also from other parts of the body—is a primary source of
biological air contaminants and of nourishment for the growth
of microorganisms. For example, it has been reported that the
body sheds skin scales at a rate, dependent upon activity level,
that averages 7 million scales per minute with an average of
four bacteria per scale. Dust mites, dermatophagoides, feed
on these scales and in turn produce fecal pellets in the respi-
rable size range that can strongly affect sensitive individuals.
Almost all surfaces containing organic material such as
cloth fabrics, paper, wood, leather, adhesive ceiling tiles,
paint, soaps, and greases under proper conditions can sustain
the growth of fungi, bacteria, acarids, and other microbes.
Locations indoors where water can stagnate or cause con-
tinuous dampness of surfaces—for example, chilled-water
air-conditioning systems, refrigerator drip pans, bathrooms,
flooded basements, hot tubs, and saunas—are possible
sources of biological pollutants.Aerosol formation originating from water reservoirs is
an important mechanism for airborne transmission of dis-
ease. The “jet-drop” phenomenon that occurs in washbasins,
bathtubs, toilet bowls, and urinals can generate aerosolized
microorganisms, as can the high-speed water-cooled drills
used by dentists. Humidifiers that generate steam by other
than thermal means can be dangerous sources of microor-
ganisms that have grown inside the reservoirs; therefore, they
should be sterilized before use and will always form droplets
containing the minerals in the water being used. Filters in
ventilating systems, if not properly cleaned and maintained,
can also become significant sources of infectious diseases.
Some organisms are not able to survive for long periods
outside a host and thus require rapid person-to-person transfer
to cause serious problems, but others can remain viable for
long periods and thus carry the diseases that are recognized as
transmittable through air. The following are some of the major
diseases that are classified as human airborne infections.Tuberculosis Diphtheria
Rheumatic fever Meningococcus menin-
Scarlet fever gitis
German measles Psittacosis
Smallpox Measles
Chicken pox Whooping cough
Hemolytic streptococci Poliomyelitis
Pneumococcus pneumonia Systemic mycosis
Mycoplasma pneumonia Mumps
Influenza The common coldCertain lesser-known diseases have been brought into
focus by investigators of illnesses attributed to indoor air
pollution. Some of these have been associated with con-
taminated water reservoirs in humidifiers, chilled-water
air-conditioning systems, and other adjuncts to indoor ven-
tilation and climatization.
The most notable infection is Legionnaires’ disease,
which has caused a number of epidemics, including the one
at the Legionnaires Convention in Philadelphia in 1977,
which resulted in 182 cases, 25 of which were fatal. The
infection is caused by a not-uncommon soil bacterium,
Legionella pneumophilia, which survives very well in water
and can thus contaminate cooling towers, air conditioners,
and other potential sources of aerosols. Drinking water in a
hospital has also been implicated in the transmission of this
infection. Since its discovery, studies have claimed that 10
to 15% of pneumonia cases in hospitals are attributable to
legionella.
A milder, self-limiting disease with flulike symptoms
called Pontiac fever is also attributed to legionella.
Tuberculosis is caused by a virulent microorganism,
mycobacterium tuberculosis, which can survive for long
periods is encapsulated form and has been shown to be read-
ily transmitted through ventilation systems. The gradual dis-
appearance of this disease has been reversed in areas where
AIDS is prevalent, therefore, its importance as a public-
health problem is increasing.C001_003_r03.indd 40 11/22/2005 11:06:07 AM