Environmental Engineering Reference
In-Depth Information
from each other and represent no difference in risk. For many homeowners,
the difference is one of life and death or the difference between mitigating
and not mitigating. For real estate transactions, it may be the difference
between a deal maker or a deal breaker or the cost of installing a radon
control system.
The risks of radon exposure in residences are real. Cancer risks are sig-
nificantly greater than the 1 per 10
6
risk of cancer used by USEPA to regulate
a number of cancer-causing substances. The risks are, however, different, in
that radon is a naturally occurring substance and thus a risk attributable to
nature. The risk is imperceptible to most humans and is long term. Thus it
appears to cause less alarm than other cancer-causing substances.
III. Lead
Lead is a heavy metal which occurs naturally in soil, water, and to a more
limited degree, ambient air (as mineral particles). It is found in the earth's
crust in a number of different minerals. Metallic lead, characteristically blu-
ish-gray in color, is extracted from relatively rich mineral ores such as galena
(PbS), cerussite (PbCO
3
), and angelsite (PbSO
4
). In addition to its elemental
form, it has two oxidation states, Pb(II) and Pb(IV).
Because of its relatively low melting point (327°C), malleability, and
other desirable properties, lead is, and has been, the most widely used (based
on mass) nonferrous metal. Humans have used it for over 8 millennia. As a
result of the smelting of metal ores, combustion of lead-amended gasoline,
and other uses, lead contamination of the environment is ubiquitous. Lead
levels above background concentrations can be found in soil, drinking water,
rivers and streams, plants, and polar ice. Indeed, ice core concentrations can
be used to track the historical use of lead by humans.
In the past century, lead has been used as a pigment in paints; to man-
ufacture storage batteries; and in the production of solders, munitions, plas-
tics, and a variety of products. Until relatively recently, organic lead com-
pounds (tetramethyl and tetraethyl lead) were widely used in North America
to boost the octane rating of gasoline and serve as a scavenger for free
radicals (antiknock agent).
Lead use has varied over the century. Because of health and environ-
mental concerns, its use as a pigment in paint, gasoline fuel additive, and
in soldering compounds has declined greatly, particularly in North America.
Its use in storage battery production has, on the other hand, increased
significantly.
Because of its widespread use, humans have been, and continue to be,
exposed to lead concentrations well above background levels. Notable his-
torical exposures have occurred from acidic liquids stored in lead containers
(Roman and medieval times), inhalation of lead dusts from primary and
secondary lead smelters, ingestion of food from lead-soldered cans, leaching
from plumbing materials, inhalation of airborne lead dusts associated with
