Civil Engineering Reference
In-Depth Information
Mercury
Sources
Mercury, one of the least abundant elements in the earth's crust, has three
oxidation states:
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Elemental mercury
•
Mercurous compounds
•
Mercuric compounds
•
Mercury may be detected in at least 30 ores, and occurs in water primarily as an
inorganic salt, and as organic mercury in sediments. A major natural source of mercury
is the degassing of the earth's crust, which releases an estimated 25,000 to 150,000
tons of mercury per year.
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Anthropogenic sources include burning of fossil fuels, metal
refining operations, chloralkali plants, sewage discharges, and past uses of mercury-
containing pesticides.
Occurrence
Mercury detected in potable water is predominantly in the form of
inorganic mercury. Maximum concentrations reported by EPA are:
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Groundwater
30 percent above 0.5
g / L from 106 supplies sampled
Surface water
14 percent above 2.0
g/L
Surface water
32 percent surface water with 0.5
g / L from 31
supplies sampled and 16 percent above 2
g/L
Health Effects
The comparative toxicity of different forms of mercury is related to
their ability to be absorbed by humans. Inorganic mercury is poorly absorbed into the
adult GI tract, does not readily penetrate cells, and is not as toxic as methyl mercury.
However, the absorption of inorganic mercury can be much higher in infants and young
children.
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The principal target organ of inorganic mercury is the kidneys, with neu-
rologic and renal disturbances.
Organic forms, such as methyl mercury, are readily absorbed and easily enter the
central nervous system, causing death or mental and motor dysfunctions. The fact that
certain microorganisms can convert inorganic and organic forms of mercury to the
very toxic methyl or dimethyl form makes any form of mercury potentially dangerous
in the environment.
Mercury intoxication can be acute or chronic. Acute intoxication usually is the
result of self-inflicted or accidental exposure. Acute poisoning results in pharyngitis,
gastroenteritis, vomiting, and bloody diarrhea initially, followed by such systemic ef-
fects as anuria with uremia, stomatitis, ulcerative-hemorrhage colitis, nephritis, hepa-
titis, and circulatory collapse. The inhalation of mercury vapor or dusts leads to the
typical symptoms of mercury poison with lesions of the mucous membranes.
Chronic mercury poisoning results from exposure to small amounts of mercury over
extended periods of time. Typically, chronic poisoning by inorganic mercurials is the
result of accidents or environmental contamination. Workers who are continually ex-
posed to inorganic mercury are susceptible to chronic mercurialism. Chronic alkyl
mercury poisoning, known as Minamata disease, is insidious because the onset of
mercurialism can take weeks or even years. This type of poisoning is characterized
by major neurological symptoms that lead to permanent damage or death.
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