Civil Engineering Reference
In-Depth Information
Health Effects
Selenium is an essential dietary element, with most intake coming
from food. The levels found in food reflect local soil conditions.
Some selenium compounds are toxic to humans, with hydrogen selenide being one
of the most irritating and toxic compounds. The poisoning symptoms are similar to
those of arsenic poisoning. In industrial situations, human exposure is through the skin
and lungs as a result of exposure to dust or fumes.
Chronic exposures to selenium, either by ingestion or through inhalation of dust
and fumes, have resulted in depression, nervousness, occasional dermatitis, gastroin-
testinal disturbances, giddiness, and a garlic odor.
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Epidemiological studies have shown
an increase in the incidence of dental caries in children when small amounts of sele-
nium were ingested as part of their diets.
Although selenium can be toxic to humans and animals, it is usually the result of
accidental exposure. Selenium reacts in vivo with other elements, protecting against
heavy metal toxicity from mercury, cadmium, silver, and thallium.
Naturally occurring selenium compounds have not been shown to be carcinogenic
in animals. Selenium may inhibit tumor formation. EPA has not classified the carcin-
ogenicity of selenium (Group D) because of inadequate evidence.
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Silver
Sources
The average concentration of silver in soil is 0.1 ppm, whereas, in the
earth's crust, it is 0.07 to 0.08 ppm. Chloride sulfide, phosphate, and arsenate are
insoluble. Silver nitrate is highly soluble; silver sulfate is moderately soluble.
Occurrence
One survey found silver in 309 out of 677 groundwaters with concen-
trations ranging from 0.1 to 9
g / L, and 50 out of 109 surface waters with silver
concentrations of 0.1 to 4
g/L.
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A survey of potable water in the 100 largest cities in the United States found a
mean silver concentration of 0.23
g / L, with a low of 0 and maximum of 7.0
g/L.
Another survey of drinking water produced a mean of 2.2, minimum of 0.3, and a
maximum of 5
g / L, with a frequency of detection of 6.1 percent.
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Health Effects
Silver is a nonessential element, providing no beneficial effects from
its ingestion in trace amounts. Acute toxicity can result from large single doses, and
can be fatal. Poisoning victims experience pulmonary edema after exhibiting anorexia
and anemia.
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Chronic toxicity takes the form of an unsightly blue-gray discoloration of the skin,
mucous membranes, and eyes, which is called argyrosis or argyria. Apparently, besides
the cosmetic changes, there are no physiologic effects. Ingestion of trace amounts of
silver or silver salts results in its accumulation in the body, particularly the skin and
eyes. There is some evidence that changes to the kidneys, liver, and spleen can occur.
Silver shows no evidence of carcinogenicity or mutagenicity.
Sodium
Sources
Sodium is the sixth most abundant element on earth and is found in nature
only in combined forms. Sodium compounds are used in paper, glass, soap, textile,
petroleum, chemical, and metal industries. The most common compounds are:
