industries which specialize in the science,
technology, and processing of metals; these plants produce highly
concentrated and toxic wastes which can contribute to pollution of
ground water and air when not properly disposed.

Noxious substances - injurious, very harmful to living beings.

Overgrazing - the grazing of animals on plant material faster than it
can naturally regrow leading to the permanent loss of plant cover, a
common effect of too many animals grazing limited range land.

Ozone shield - a layer of the atmosphere composed of ozone gas (O3)
that resides approximately 25 miles above the Earth's surface and
absorbs solar ultraviolet radiation that can be harmful to living
organisms.

Poaching - the illegal killing of animals or fish, a great concern with
respect to endangered or threatened species.

Pollution - the contamination of a healthy environment by man-made
waste.

Potable water - water that is drinkable, safe to be consumed.

Salination - the process through which fresh (drinkable) water becomes
salt (undrinkable) water; hence, desalination is the reverse process;
also involves the accumulation of salts in topsoil caused by
evaporation of excessive irrigation water, a process that can
eventually render soil incapable of supporting crops.

Siltation - occurs when water channels and reservoirs become clotted
with silt and mud, a side effect of deforestation and soil erosion.

Slash-and-burn agriculture - a rotating cultivation technique in which
trees are cut down and burned in order to clear land for temporary
agriculture; the land is used until its productivity declines at which
point a new plot is selected and the process repeats; this practice is
sustainable while population levels are low and time is permitted for
regrowth of natural vegetation; conversely, where these conditions do
not exist, the practice can have disastrous consequences for the
environment.

Soil degradation - damage to the land's productive capacity because of
poor agricultural practices such as the excessive use of pesticides or
fertilizers, soil compaction from heavy equipment, or erosion of
topsoil, eventually resulting in reduced ability to produce
agricultural products.

Soil erosion - the removal of soil by the action of water or wind,
compounded by poor agricultural practices, deforestation, overgrazing,
and desertification.

Ultraviolet (UV) radiation - a portion of the electromagnetic energy
emitted by