Aside from some special circumstances involving radionuclides from military
production facilities, the greatest concern with respect to these materials in water arises
from natural geological sources. Specifically, the alpha particle emitter radium-226,^226 Ra,
half-life 1620 years, is a particular concern in drinking water. A number of municipal
water supplies contaminated with this radionuclide by leaching into groundwater from
rock formations underground have been shut down because of the hazard presented.
Immediately following World War II, aboveground testing of nuclear weapons
was a significant source of environmental pollution of radionuclides. Nuclear bombs
typically detonated on towers in remote regions of New Mexico, Nevada, and Russia
would generate large quantities of uranium fission products and would produce more
radionuclides by the absorption of neutrons from the bomb by dirt and sand. A large
mass of radioactive dust and debris would be entrained in a rapidly ascending column of
hot gases and dispersed throughout the world. “Fallout” from these tests got onto land,
causing particular concern about strontium-90 falling on pastureland and getting into
cow’s milk. Radionuclides were also scavenged from the atmosphere by rainfall, which
could get into water supplies. The radioactive products of most concern from these tests
were of elements that the body recognizes as material to be incorporated into tissue.
These were strontium-90 (^90 Sr), half-life 28 years, which is in the same chemical group as
calcium and is incorporated into bone; cesium-137, (^137 Cs), an alkali metal that the body
handles much like sodium and potassium ions; and iodine-131 (^131 I), half-life 8 days,
that is attracted to the thyroid and can impair its function and even cause thyroid cancer.
The banning of above-ground nuclear weapons testing has largely stopped release of
these elements to the environment. The last and largest such release was the catastrophic
explosion and fire at the Soviet power reactor at Chernobyl in 1986 (see Section 6.9).
Fortunately, radionuclides are easily and sensitively detected in water. The most
common such contaminant, radium-226, is readily removed by water softening processes
that involve treatment of water with lime.
All nations seem to be abiding well with international treaties forbidding aboveground
testing of nuclear weapons, so that should not be a source of radionuclide contamination.
We can hope that there will not be any hostile exchanges of nuclear weapons in the future.
Improperly disposed radionuclides remain a threat to some water supplies. One example
is a reported plume of radioactive groundwater flowing from the Hanford atomic energy
installation to the Columbia River in Washington State.
7.17. Water Treatment
Municipal Water
Water requires varying degrees of treatment before it is used for households or
for industrial applications. Furthermore, wastewater from sewage or from industrial
applications normally must be treated before it is released. Some of the basic treatment
processes are similar, regardless of the intended use or mode of disposal of the water.
They are discussed briefly here for municipal water, and some of the specialized treatment
processes applied to wastewater are summarized at the end of the chapter.
Chap. 7. Water, The Ultimate Green Solvent 185