Geoscience Reference
In-Depth Information
Contamination of lead in groundwater originates from the dissolution of lead
from soil and the earth's crust. Lead particulate from the combustion of leaded
gasoline and ore smelting can contaminate local surface water by surface runoff.
Lead itself is only of minor content in the earth's crust. A wide distribution of lead
in sedimentary rock and soils has been reported, with an average lead content of
10 mg/kg (10 ppm) in topsoil, and a range of 7-12.5 ppm in sedimentary rock
(EPA
1992
). In soils, lead generally is present in the form of carbonates and
hydroxide complexes. Strong absorption by soil and complexation by humus can
further limit lead concentrations in surface waters and groundwater.
Lead poisoning is an environmental and public health hazard of global pro-
portions. Children and adults in virtually every region of the world are being
exposed to unsafe levels of lead in the environment. In fact, children are exposed
to lead from different sources, such as paint, gasoline, and solder, and through
different pathways such as air, food, water, dust, and soil. Poisoning can occur
from a single, high-level exposure or the cumulative effect of repeated high- or
low-level exposures.
The adverse health effects of lead are indicated by blood levels, which cause
changes in blood pressure at 10 lg/dL, to severe retardation and even death at very
high blood levels of 100 lg/dL. For example, lead interferes with synthesis of red
blood cells and causes anemia, kidney damage, impaired reproduction function,
interference with vitamin D metabolism, and delayed neurological and physical
development. For adult men, high blood lead can cause elevated blood pressure,
hypertension, strokes, and heart attack. Pregnant women exposed to lead are at risk
of complications in their pregnancies, shorter gestational period, and damage to
the fetus.
3.5.5 Nickel
Nickel is a silver-white, lustrous, hard, malleable, ductile, ferromagnetic metal that
is relatively resistant to corrosion and is a fair conductor of heat and electricity.
Nickel is a ubiquitous trace metal that occurs in soil, water, air, and in the bio-
sphere. The average content in the earth's crust is about 0.008 %. Nickel ore
deposits are accumulations of nickel sulfide minerals (mostly pentlandite) and
laterites. Nickel exists in five major forms: elemental nickel and its alloys; inor-
ganic, water-soluble compounds (e.g., nickel chloride, nickel sulfate, and nickel
nitrate); inorganic, water-insoluble compounds (e.g., nickel carbonate, nickel
sulfide, and nickel oxide); organic, water-insoluble compounds; and nickel car-
bonyl Ni(CO)
4
.
Nickel is used mostly for the production of stainless steel and other nickel
alloys with high-corrosion and temperature resistance. Nickel alloys and nickel
platings are used in vehicles, processing machinery, armaments, tools, electrical
equipment, household appliances, and coins. Nickel compounds also are used as
catalysts, pigments, and in batteries.
