Civil Engineering Reference
In-Depth Information
Epidemiological studies can be used to determine the safe quantity of mercury
ingestion. The lowest concentration associated with methylmercury toxic symptoms is
0.2
g / g. This corresponds to prolonged continuous exposure of 0.3 mg / 70 kg body
weight / day. Using a margin of safety of 10, the maximum intake from all sources
(air, water, and food) is 0.03 mg / person / day.
EPA has not classified the carcinogenicity of mercury (Group D) because of in-
adequate evidence.
Molybdenum
Sources
Molybdenum does not occur as an element in nature; it is obtained from
molybdenite (MoS
2
) and minor commercial ores, such as wulfenite (PbMoO
4
), or as
a by-product of copper and tungsten mining operations. It is used in metallurgy in
either a metal or salt form. Principal applications include nuclear energy, military use,
electrical products, petroleum industry, glass and ceramics industries, and production
of pigments.
Occurrence
A 1970 survey of finished waters found molybdenum in 30 percent of
the samples, with a mean of 85.9
g / L and a range of 3 to 1,024
g/L.
2
Other surveys
produced mean values of 8.0
g / L in 30 percent of positive samples, ranging in this
group from 1.1 to 52.7
g / L, with some high readings of 1 mg / L.
2
Health Effects
Molybdenum is considered an essential trace element in humans.
There is no apparent bioaccumulation of this element in animal or human tissues.
Molybdenum is readily absorbed by the gastrointestinal tract, with concentration in
the liver, kidneys, and bones. Chronic exposure can result in weight loss, bone ab-
normalities, and male infertility.
EPA has not classified the carcinogenicity of molybdenum (Group D) because of
inadequate evidence.
Nickel
Sources
Nickel is found in many ores, such as sulfides, arsenides, antomonides,
oxides, and silicates. The chief source is chalcopyrite, with other sources including
pyrrhotite, pentlandite, ganierite, niccolite, and millerite. Nickel salts are soluble in
water, as are many of its compounds. Nickel is extensively used in making stainless
steel, Invar, Monel, Inconel, and corrosion-resistant alloys. It is also used in ceramics,
special batteries, electronics, and space applications. Nickel is not commonly found in
nature as a pure metal.
Occurrence
Nickel is common in drinking water. EPA's Community Water Supply
Survey detected nickel in 86 percent of groundwater supplies and 84 percent of surface
supplies tested.
3
In finished water supplies, a mean concentration of nickel was cal-
culated at 34.2
g / L, with a range from 1 to 490
g / L. In another survey, an average
value was 4.8
g / L, with a maximum of 75
g/L.
2
Health Effects
Nickel is an essential element for animals, but nickel nutritional
deficiency has not been recognized in humans. Interpolating animal studies to humans,
a nutritional need for a human would be on the order of 50
g / day. Nickel has low
