Environmental Engineering Reference
In-Depth Information
know whether Duncan suffered permanent damage from the higher
mercury level, but children have suffered losses in IQ at concentrations
of only 5.8 milligrams.
Mercury was not the only contaminant in the lakes and reservoirs
analyzed by the EPA. Polychlorinated biphenyls (PCBs), banned in the
late 1970s but still present in the environment, were present in 17 percent
of the water bodies. PCBs have been linked to cancer and other health
effects.
A ray of hope surfaced in 2009 with the EPA's announcement in its
annual Toxics Release Inventory that water pollution decreased by 5
percent between 2006 and 2007. However, releases of PCBs into the
environment increased by 40 percent due to disposal of supplies manu-
factured before the substances were banned in 1979. Mercury releases,
mostly due to mining, increased by 38 percent. Dioxin releases increased
by 11 percent, and lead releases increased by 1 percent. Releases of all
persistent, bioaccumulative, and toxic chemicals or metals increased by
1 percent. These increases will likely be refl ected in water analyses over
the next few years.
That chemicals in combination can be more deadly than either chemi-
cal alone and in lower concentrations was recently demonstrated in a
study of salmon by federal scientists.
40
Five of the most common pesti-
cides used in California and the Pacifi c Northwest acted in deadly synergy
by suppressing an enzyme that affects the nervous system of salmon.
Some fi sh died immediately. Exposures to a single chemical, however,
did no harm. As expected, harmful effects on the salmon were observed
at lower pesticide levels when chemicals were applied in combinations.
Earlier studies had found that three of the pesticides can be lethal to
salmon and can inhibit their growth by impairing their ability to smell
prey, impair their ability to swim, and make it diffi cult to spawn and
avoid predators.
More than 2,300 chemicals that can cause cancer have been detected
in U.S. drinking water. Although the amounts are usually small and
considered safe by the EPA, the surgeon general has stated, “No level of
exposure to a chemical carcinogen should be considered toxicologically
insignifi cant to humans.”
41
Seventy years ago in the United States, one person in fi fty could expect
to get cancer in his or her lifetime. Today one in three people and one
in two males can expect to get cancer. The risk that a fi fty-year-old white
woman will develop breast cancer soared to 12 percent from 1 percent
in 1975. Studies reveal that 90 percent of breast cancer cases are not
