Geoscience Reference
In-Depth Information
9.1.7.3. Health Effects
222
Rn, a gas, is not itself harmful, but its progeny,
218
Po
and
214
Pb, which enter the lungs directly or on the sur-
faces of aerosol particles, are believed to be highly
carcinogenic (Polpong and Bovornkitti, 1998). Any
activity increasing the inhalation of aerosol particles
enhances the risk of inhaling radon progeny; thus, the
combination of radon and cigarette smoking increases
lung cancer risks above the normal risks associated with
smoking (Hampson et al., 1998). Whereas several stud-
ies argue that a link exists between high radon levels and
enhanced cancer rates (Henshaw et al., 1990; Lagarde
et al., 1997), other studies argue that no such link exists
(Etherington et al., 1996). Nevertheless, radon progeny
were the second largest cause of lung cancer in the
United States after smoking in 2007, causing about
21,000 lung cancer deaths (U.S. EPA, 2009c). Of these,
about 18,000 occurred in smokers and 3,000 in non-
smokers, indicating that radon exacerbates the health
effects of smoking.
Figure 9.3.
First evidence of radioactivity, along with
Becquerel's notes. Edgar Fahs Smith Collection,
University of Pennsylvania Library.
particles that are inhaled (Cohen, 1998). In the lungs
or in ambient air,
214
Pb decays to bismuth-214 (
214
Bi),
which decays to polonium-214 (
214
Po).
214
Po decays
almost immediately to lead-210 (
210
Pb), which has a
lifetime of 22 years and usually settles to the ground if it
has not been inhaled. It decays to bismuth-210 (
210
Bi),
then to polonium-210 (
210
Po), and then to the stable
isotope, lead-206 (
206
Pb), which does not decay further.
9.1.8. Volatile Organic Compounds
Vo latile organic compounds
(VOCs) are organic
compounds that have relatively low boiling points
(50
◦
C-260
◦
C). Because of the their low boiling points,
VOCs often evaporate from materials containing them.
Sources of VOCs indoors include adhesives, solvents,
building materials, combustion appliances, paints, var-
nishes, tobacco smoke, room deodorizers, cooking, car-
pets, furniture, and draperies. More than 350 VOCs
with mixing ratios greater than 1 ppbv have been
measured in indoor air (Brooks et al., 1991). Carpets
alone emit at least 99 different VOCs (Sollinger et
al., 1994). Some common VOCs in indoor air include
propane, butane, pentane, hexane, n-decane, benzene,
toluene, xylene, styrene, acetone, methylethylketone,
and limonene, among many others. VOC mixing ratios
indoors can easily exceed those outdoors by a fac-
tor of 5 (Wallace, 1991). Many VOCs are hazardous.
The health effects of some VOCs were described in
Table 3.15.
9.1.7.2. Concentrations
Outdoor radon concentrations are generally low and
do not pose a human health risk. However, because
of the lack of ventilation in many houses, indoor con-
centrations can become thousands of times larger than
outdoor concentrations (Wanner, 1993). Indoor concen-
trations depend on the abundance of radon in soil and
the porosity of floors. Nero et al. (1986) found mean
indoor concentrations of
222
Rn in 552 homes as 56 Bq
(becquerels) m
−
3
,where a
Becquerel unit
is the num-
ber of disintegrations of atomic nuclei per second to
another isotope or element. A variety of other stud-
ies found indoor concentrations of 46 to 116 Bq m
−
3
(Jones, 1999). Marcinowski et al. (1994) estimated that
about 6 percent of U.S. homes contained radon concen-
trations in excess of U.S. EPA levels considered safe
(148 Bq m
−
3
). Radon levels in homes can be reduced
by installing check valves in drains, sealing basement
walls and floors, and installing fans in crawl spaces to
speed mixing of outside air with radon-laden air under
the house.
9.1.9. Allergens
Allergens
are particles such as pollens, foods, or
microorganisms that cause an allergy, which is an
abnormally high sensitivity to a substance. Symp-
toms of an allergy include sneezing, itching, and skin
rashes. Indoor sources of allergens are dust mites, cats,
dogs, rodents, cockroaches, and fungi. Pollens originate
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