Environmental Engineering Reference
In-Depth Information
tanks. A spokesman for Maryland's health department warned that
people should not let cuts or open wounds contact the water.
Other Dead Zones
Pesticides and artifi cial fertilizers are used in massive amounts on Amer-
ica's farms, and most of it washes off the farms, into local streams, and
eventually into the Mississippi River. In addition to making about half
the streams and rivers in the watershed unsafe for drinking, swimming,
or recreational contact, the pollution has created a dead zone in the
nearshore Gulf of Mexico near the mouth of the river. It covers about
8,000 square miles, the size of Massachusetts, and has been growing
since measurements began in 1985.
The hypoxia—very low levels of dissolved oxygen—is caused mainly
by excess nitrogen from fertilizer used on crops, with corn using the
most. The dissolved nitrogen fl ows into the Gulf and spurs the growth
of excess algae. The algae cause an oversupply of organic matter that
decays on the Gulf fl oor, depleting the water of oxygen. There are no
fi sh, shrimp, or crabs in the dead zone and little marine life of any kind.
Fish that survive in areas with slightly higher levels of oxygen have
reproductive problems.
Numerous dead zones can be found around the coastline of the United
States and at 405 locations worldwide. In most cases, the cause is the
same: runoff of artifi cial fertilizer into nearshore waters.
A piece of hopeful news arrived in 2007 when North America's fi rst
full-scale commercial water treatment facility capable of removing phos-
phorous began operating in Edmonton, Canada. It is also possible to
remove nitrogen but the process is not yet widespread.
Endocrine Disrupters
Among the many well-publicized concerns about specifi c pollutants such
as lead and mercury in water is a group of chemicals that affect our
sexual characteristics.
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Apprehension is growing among scientists that
the cause of these maladies may be a class of chemicals called endocrine
disrupters, widely used in agriculture, industry, and consumer products.
Some also enter the water supply when estrogens in human urine pass
through sewer systems and then through water treatment plants.
These chemicals interfere with the endocrine system in our bodies, a
system that regulates many functions such as growth, development and
maturation, and the way various organs operate.
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There are 966 known
or suspected endocrine-disrupting chemicals in existence, and often they
