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What
is Hydrogen Sulfide?
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A
colorless, flammable poisonous gas, H2S, having a characteristic
rotten-egg odor and used as an antiseptic, a bleach,
and a reagent.
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What
is Chlorine?
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Chlorine
is a greenish-yellow, poisonous gas with a disagreeable, suffocating
odor. Chlorine is soluble in water; chlorine water has strong
oxidizing properties. Chlorine is used in water purification,
and as a disinfectant and antiseptic. Chlorinated hydrocarbons
(e.g., DDT) are long-lasting pesticides and have become troublesome
environmental pollutants. Many poison gases contain chlorine.
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What
is Lead?
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Lead
is silver-blue, dense, relatively soft, and malleable, with
low tensile strength. Lead compounds (all poisonous) include
tetraethyl lead (a gasoline antiknock additive now used mainly
in developing countries) and oxides used in mordants and pigments.
Continued exposure to lead—through inhalation of fumes
or sprays and ingestion of food containing lead —can
result in a cumulative chronic disease called lead poisoning.
It was once a serious occupational hazard, but protective equipment
and other precautionary measures have reduced its incidence.
Lead poisoning remains a serious problem in children, who are
more susceptible to it. Causes may include ingestion of paint
chips from peeling walls or pipes or inhalation of contaminated
dust during home renovation.
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What
is Cadmium?
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Cadmium
is a silver-white, lustrous, malleable, ductile metal. Its major
use is as an electroplated coating on iron and steel to prevent
corrosion; it is also used in nickel-cadmium batteries.
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What
is Radon?
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Radon
is a gaseous radioactive element, discovered by Ernest Rutherford
in 1899. A colorless, chemically unreactive inert gas, it is
the densest gas known. Highly radioactive (emitting alpha rays),
it is used chiefly in the treatment of cancer by radiotherapy.
In homes and other buildings in some areas of the U.S.,
radon produced by the radioactive decay of uranium-238 present
in soil and rock can reach levels regarded as dangerous,
but the seriousness of the problem is unclear.
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What
is Mercury?
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Mercury
or quicksilver is a metallic element, known to the ancient Chinese,
Hindus, and Egyptians. Silver-white and mirrorlike, it is the
only common metal existing as a liquid at ordinary temperatures.
Mercury is used in barometers, thermometers, electric switches,
mercury-vapor lamps, and certain batteries; a mercury alloy,
called an amalgam, is employed in dentistry. Mercury
compounds have been used as insecticides, in rat poisons, and
as disinfectants. Not easily discharged from the body, the metal
is a cumulative poison; its ingestion in more than trace amounts
in contaminated food or its absorption by the skin or mucous
membranes results in mercury poisoning, which can cause skin
disorders, hemorrhage, liver and kidney damage, and gastrointestinal
disturbances. Workers in many industries have been
affected, and mercury pollution of rivers, lakes, and oceans,
usually through the discharge of industrial wastes, has become
a serious environmental problem. Most mercury pesticides have
been withdrawn from the U.S. market, and in 1972 more than 90
nations approved an international ban on the dumping of mercury
in the ocean, where the metal has tended to work its way into
the food cycle of aquatic life and to reach dangerous levels
in certain food fish.
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What
is Asbestos?
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Asbestos
is a common name for any of a group of fibrous silicate minerals
resistant to acid and fire. Asbestos usually occurs as veins
in rocks and seems to be a product of metamorphism. Chrysotile
asbestos (H4Mg3Si2O9), a form of serpentine, the most important
commercial asbestos, has curly fibers. Amphibole, the other
main type, has needlelike fibers. Asbestos is produced chiefly
in Canada; asbestos products include brake and clutch linings,
water pipe, and roofing materials. Studies have shown
that amphibole asbestos particles in the air can cause lung
cancer and the lung disease asbestosis, and many former and
all new uses of asbestos in the U.S. have been banned.
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What
is Phenol?
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A
caustic, poisonous, white crystalline compound, C6H5OH, derived
from benzene and used in resins, plastics, and pharmaceuticals
and in dilute form as a disinfectant and antiseptic. Also called
carbolic acid.
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What
is Benzene?
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Benzene
is a (C6H6), colorless, flammable toxic liquid with a strong
odor. A hydrocarbon, benzene is the parent substance of the
aromatic compounds. It consists of an unusually stable hexagonal
ring of six carbon atoms, each of which is bonded to a hydrogen
atom. Derivative compounds include phenol and aniline. Obtained
from coal tar and petroleum, benzene and its derivatives are
used in making dyes, drugs, and plastics. Benzene has
been identified as a carcinogen.
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What
is a Hydrocarbon?
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A
hydrocarbon is any organic compound composed solely of carbon
and hydrogen. Hydrocarbons include aliphatic compounds, in which
the carbon atoms form a chain, and aromatic compounds, in which
the carbon atoms form stable rings. The aliphatic group is divided
into alkanes (e.g., methane and propane), alkenes, and alkynes
(e.g., acetylene), depending on whether the molecules of the
compounds contain, respectively, only single bonds, one or more
carbon-carbon double bonds, or one or more carbon-carbon triple
bonds. Petroleum distillation yields useful fractions that are
hydrocarbon mixtures, e.g., natural gas, gasoline, kerosene,
home heating oil, lubricating oils, paraffin, and asphalt. Coal
tar is also a source of hydrocarbons. Hydrocarbon derivatives
contain additional elements, e.g., oxygen, and include alcohols,
aldehydes, ketones, carboxylic acids, and halocarbons.
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What
is a Aromatic Compound?
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An
aromatic compound is any of a large class of organic compounds
including benzene and compounds that resemble benzene in chemical
properties. Aromatic compounds contain unusually stable ring
structures, often made up of six carbon atoms arranged hexagonally.
Some of the compounds, however, have rings with more or fewer
atoms, not necessarily all carbon. Furan, for example, has a
ring with four atoms of carbon and one of oxygen. Also, two
or more rings can be fused, as in naphthalene. The characteristic
properties of the class, notably the stability of the compounds,
derive from the fact that aromatic rings permit the sharing
of some electrons by all the atoms of the ring, which increases
the strength of the bonds.
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What
is a Carcinogen?
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A
carcinogen is any agent that causes cancer in animal tissue.
Ubiquitous indoors and out, in the workplace and at home, carcinogens
can be inorganic, such as asbestos and arsenic, or organic,
such as certain molds and viruses. Others include various types
of radiation, such as ultraviolet and X rays. Carcinogens
can be inhaled (radon and tobacco smoke), ingested
(nitrites), or absorbed through the skin (DDT and other
pesticides). Using a procedure called the Ames test, potential
carcinogens can be tested for their propensity to damage DNA
and cause mutations. It has been predicted that 30%
of Americans will die of cancer caused in part by environmental
carcinogens before they reach the age of 74.
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What
is DDT?
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DDT
is a colorless contact insecticide, C14H9Cl5, toxic
to human beings and animals when swallowed or absorbed through
the skin. It has been banned in the United States for most uses
since 1972.
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All definitions are from The Microsoft Bookshelf,
1996-1997 Edition.
Biology
| Chemistry | Medicine
| La Natural
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