Environmental Engineering Reference
In-Depth Information
is vitamin B
12
or cyanocobalamin. Vitamin B
12
is essential for good health
in animals and humans.
Nickel is a very hard metal that occurs naturally in soils and volcanic
dust. Nickel is used in combination with other metals to form alloys used
for coins, jewelry, and stainless steel. Nickel compounds are used for elec-
troplating, to color ceramics, and in battery production [30]. Nickel is
released into the atmosphere by windblown dust, volcanoes, combustion
of fuel oil, municipal incineration, and industries involved in nickel rei n-
ing, steel production, and other nickel alloy production. Background levels
of nickel in soils vary widely depending on local geology and anthropo-
genic inputs, but concentrations typically range between 4 and 80 ppm.
Concentrations of nickel in household dust can be high and therefore pose
an increased risk to young children.
11.3
Toxicity to Human Health and Ecosystems
It becomes a matter of alarm when metals accumulate in a locality in con-
centrations approaching or exceeding those that can harm organisms,
including human beings. Some heavy metals are essential for biological
systems in small amounts, but if ingested in larger amounts can disrupt
physiological processes. Heavy metals, such as Cd, Hg, Pb, and Sn, may
serve no particular biological function and can be toxic at relatively low
concentrations. Heavy metals tend to bioaccumulate in the food chain, and
their toxicity to organisms ranges from chronic to acute and from sublethal
to deadly.
At high exposure levels, lead causes encephalopathy, cognitive impair-
ment, behavioral disturbances, kidney damage, anemia and toxicity to
the reproductive system. In its hexavalent form, chromium is widely rec-
ognized to exert toxic ef ects on biological systems. Human exposure to
Cr(VI) compounds is associated with a higher frequency of respiratory
cancers [40]. Cadmium is associated with nephrotoxic ef ects, particularly
at high exposure levels; long-term exposure may cause bone damage as
well. High concentrations of mercury can lead to neurobehavioral disor-
ders and developmental disabilities including dyslexia, attention dei cit
hyperactivity disorder, and intellectual retardation. Excessive copper con-
centrations can lead to weakness, lethargy and anorexia, as well as damage
to the gastrointestinal tract.
Arsenic occurrence in the environment, its toxicity, health hazards, and
the techniques used for speciation analysis are well known and have been
reviewed [14, 41]. Long-term drinking water exposure causes skin, lung,
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