Environmental Engineering Reference
In-Depth Information
and is referred to as inorganic arsenic. Arsenic combined with carbon and hydrogen is
organic arsenic. The organic forms are usually less toxic than the inorganic forms. For
example, some lobsters contain sufi cient arsenic to be lethal, except that the particular
form is non-toxic. Large doses of inorganic arsenic can cause death. It is a notorious poison
and has also been implicated as a cause of some skin and lung cancers (TRI 2007).
Cadmium
Cadmium was discovered in 1817 by the German chemist Friedrich Strohmeyer, as a
by-product of the zinc rei ning process. The chemist noticed that some samples of zinc
carbonate (calamine) changed colour when heated. Pure calamine, however, did not.
Strohmeyer surmised there must be an impurity present and eventually isolated it by heat-
ing and reducing the zinc carbonate. What he isolated was cadmium metal. Strohmeyer
coined the name cadmium, derived from the Latin word
cadmia
which means
calamine
.
Cadmium metal is produced as a by-product from the extraction, smelting and rei n-
ing of the nonferrous metals zinc, lead and copper, and industrial applications for this by-
product were developed in the late nineteenth and early twentieth Centuries. Cadmium
has a wide variety of unique properties and cadmium metal and cadmium compounds are
used as pigments (cadmium-sulphide based pigments appear prominently in the paintings
of Vincent Van Gogh), stabilizers, coatings, speciality alloys, electronic compounds, but,
most of all (more than 80% of its use), in rechargeable nickel-cadmium batteries.
Cadmium is recognized to produce toxic effects on humans. Cadmium tends to accu-
mulate in the kidneys, leading to kidney dysfunction as identii ed by the increased secre-
tion of proteins in urine. Intake of cadmium is generally through the diet, in particular
vegetables, corn products and i sh. Smokers are also at risk from cadmium in tobacco.
Under normal conditions, however, adverse human health effects have not been encoun-
tered from general population exposure to cadmium.
Cadmium metal is produced as a
by-product from the extraction,
smelting and refi ning of the
nonferrous metals zinc, lead and
copper.
Cadmium tends to accumulate
in the kidneys, leading to kidney
dysfunction as identifi ed by the
increased secretion of proteins
in urine.
Chromium
Chromium was discovered at the end of the eighteenth century. The name
chromium
is derived from the Greek word
chroma
which means
colour
, since chromium reacts
with certain other materials to determine their colours. For example, the green colour
of emerald is caused by the presence of very small amounts of chromium in the crystal.
Chromium, in the form of Cr (III), is an essential trace element for humans and animals.
Its most common harmful effect on humans is chromium allergy caused by exposure to
large amounts of chromium (especially Cr (VI) compounds) in the working environment.
Chromium compounds are also assumed to be carcinogenic (RTI 2007). Environmentally,
Cr (VI) compounds are generally considered to be toxic.
Chromium is a hard, steel-grey metal that is highly resistant to oxidation, even at high
temperatures. Chromium is used in three basic industries: metallurgical, chemical and
refractory (heat-resistant applications). It is the sixth most abundant element in the Earth's
crust, where it is combined with iron and oxygen in the form of chromite ore. Russia,
South Africa, Albania and Zimbabwe together account for 75% of world chromite pro-
duction. Chromite ore has not been mined in the United States since 1961; by 1985 the
United States was completely dependent on importation for its primary chromium supply.
Chromium is released to air primarily by combustion processes and metallurgical indus-
tries. Leaching from topsoil and rocks is the most important natural source of chromium
Environmentally, Cr (VI)
compounds are generally
considered to be toxic.
Chromium is released to
air primarily by combustion
processes and metallurgical
industries.
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