38 AIR POLLUTANT EFFECTS
probability of cancer (i.e., the maximum individual risk
from the inhalation of cadmium) is2.3 10 ^3 0.3 0.69 10 ^3and the aggregate risk is1000/70 14.3Risk assessment has become increasingly important but also
more complex as the basis for the management of exposures.
The EPA issues guidelines for assessing the risks of carcin-
ogens, mutagens, developmental toxicants, and chemical
mixtures together with guidelines for estimating exposures.
The Integrated Risk Information System (IRIS) is an elec-
tronic database maintained by EPA that contains information
on the human health effects that can result from exposure to
hazardous pollutants. The EPA provides telephone, fax, and
e-mail contacts for obtaining information about hazardous
pollutants.DIOXINThe term “dioxin” refers to a group of compounds that cause
similar adverse health effects. They belong to three classes
of chemicals: chlorinated dibenzo-p-dioxins (CDDs), chlo-
rinated dibenzofurans (CDFs), and polychlorinated biphe-
nyls (PCBs). Studies to date indicate that the compound
2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) is the more
toxic substance. CDDs and CDFs are not created on pur-
pose but result as by-products of certain activities; PCBs
were produced for use in transformers and other purposes,
but their use has now been prohibited. Combustion of cer-
tain materials, chlorine bleaching of pulp and paper, and
certain chemical manufacturing processes all may create
small amounts of dioxins.
Dioxins are characterized as likely human carcinogens,
with the compound TCDD considered a human carcinogen
on the basis of available human and animal data. The cancer
risk to the population from exposures to dioxins is estimated
to be 1 in 1000, with the likelihood that the risk may be much
lower. Adverse health effects have been associated with per-
sonnel exposed to Agent Orange in Vietnam because of its
dioxin content. Based upon available data, there is no clear
indication that the general population is suffering health dis-
eases from exposure to dioxins.INDOOR AIRIndoor air quality became important to those responsible for
protection against adverse health effects caused by the inhala-
tion of pollutants when it was realized that most individuals
spend 90% of their time indoors and that indoor air quality is
deteriorated by a large variety of sources. Four organizations—
the American Lung Association, EPA, Consumer ProductSafety Commission, and American Medical Association—
prepared a document titled Indoor Air Pollution in 1989 that
presents a summary of information for health professionals
about the causes and effects of indoor air pollution. Figure 4
from this document provides an overview of the effects of air
pollutants and their causes.
From a practical standpoint, the most important factor in
the control of indoor air pollution is the quality of the ven-
tilation of occupied space. The reduction of energy costs by
cutting down on forced ventilation can lead to “sick build-
ing syndrome,” the term applied to outbreaks of complaints
as a result of poorly ventilated indoor spaces. The National
Institute for Occupational Safety and Health has investigated
many cases of indoor air-quality health hazards and has pub-
lished guidelines for such investigations.
In certain cases, air-quality standards are met outdoors
but not indoors. For example, an investigator who measured
indoor versus outdoor levels of suspended particulate matter
found that he spent 84% of his time indoors, and that 82.3%
of his exposure was attributable to indoor air. The aver-
age indoor levels of nitrogen dioxide of 95 homes in rural
Wisconsin was higher than the outdoor level, sometimes
exceeding the ambient air-quality standard.SECONDHAND SMOKEThe mixture of combustion products from the burning end
of tobacco products and the smoke exhaled by smokers is
referred to as “environmental tobacco smoke” or “second-
hand smoke.” It contains more than 4,000 chemicals, more
than 50 of which are cancer-causing agents. It is associated
with an increase in lung cancer and coronary heart disease and
is particularly dangerous to the not yet fully developed lungs
of young children, increasing their risk for sudden infant death
syndrome, asthma, bronchitis, and pneumonia. An estimated
3,000 lung-cancer deaths and 35,000 coronary-heart-disease
deaths occur annually among adult nonsmokers in the United
States as a result of exposure to secondhand smoke. In chil-
dren it is estimated that 8,000 to 26,000 new asthma cases and
15,000 to 300,000 new cases of bronchitis and pneumonia for
those less than 18 months are the result of inhaling second-
hand smoke.INDOOR RADON LEVELSNext to cigarette smoking, the inhalation of radon gas and the
products of its radioactive disintegration are considered the
most significant cause of lung cancer. The EPA has estimated
that 20,000 of the lung-cancer deaths expected annually can
be ascribed to radon, and the surgeon general has attributed
85% of lung-cancer deaths to smoking.
Radon-222, an odorless, colorless radioactive gas, is one
of the products in the chain of decay of elements starting
with uranium-238 in the soil, which after radon goes on to
produce polonium isotopes 218 and 214. Their alpha-particle
emissions dissipate their energy while destroying lung tissue,C001_003_r03.indd 38 11/22/2005 11:06:06 AM