Lead
According to the Federal Agency for Toxic Substances and Disease Registry, "The lead
problem in the United States can be expressed in a simple statement: Lead is
potentially toxic wherever it is found, and it is found everywhere."
Lead is a soft, silvery, naturally occurring metal that tarnishes when exposed to air
becoming a dull bluish-gray. The chemical symbol for lead on the periodic table of
elements is Pb, from the Latin word plumbum (waterworks) due to its extensive use
in water pipes since ancient times. Lead is also combined with many other
substances to form numerous compounds. Occupational exposure to lead can occur
in a variety of ways, including, but not limited, to melting and casting pure lead or
lead alloys, soldering, molding, and the removal or abatement of lead and/or
materials or compounds that contain lead.
Since 1910 an estimated 4.2 million tons of lead have been used in white paint alone
in the United States and approximately 3 million tons of lead is estimated to remain
in and around communities with housing built before 1980. Approximately 16 percent
of all homes built prior to 1980 have concentrations of lead in the soil adjacent to the houses that exceed the previous U.S. EPA guideline of 2,000 parts per million. The chance of this occurring is at least four to five times greater if the house has exterior lead-based paint than if it does not.
Lead-based paint is a major source of lead exposure and contamination for children.
Children under the age of 6 years are likely to place various objects and substances
in their mouths. When children in this age group come in contact with chipped or
peeling lead containing paint it is likely they will ingest it.
Another source of lead contamination results from renovation or abatement projects
in which safe work practices were not used or incorrectly used. Lead in all of its various compounds, alloys, and forms is believed to have the widest range of applications of any metal with the possible exception of iron. In addition to
water pipes in old buildings, lead is used in solder for electrical circuit connections, as acid resistant drain piping in laboratories, and as a shielding material for telephone and television cables, in the walls of rooms housing X-ray equipment to prevent radiation from affecting persons in adjoining spaces, and lead in blocks and other forms is used to shield people from work with highly radioactive materials and from electromagnetic fields present in computer monitors and cathode ray tubes.
Lead acetate is often used for the preparation of other lead salts, as a mordant in
cotton dyes, as a coating for metals, as a drier in paints, varnishes, and pigment
inks, and as a colorant in hair dyes. It is also used in anti-fouling paints,
waterproofing, insecticides, and has been used in dilute solutions for the treatment of poison ivy. Lead phosphate is used as a stabilizer in styrene and casein plastics and in small amounts in the manufacture of special types of glass. Lead salts are also used in pigments for oil paints and water colors; for staining glass, crockery, and porcelain; for the production of conductive coatings on glass, pottery, porcelain, and chinaware; as a flux for porcelain painting; in the making of cements and putty; in the manufacture of parchment; in the printing of fabrics, the dyeing of cloth, and the weighting of silks and other fabrics; in analytical chemistry; in bronzing, gold pencils, mosaic gold, printing and photography; for the production of iridescent colors on brass and bronze; for the glazing of earthenware; as a selective oxidizing agent in organic syntheses; in protective coatings for iron and steel; in pencils that can write on glass; and in storage batteries.
A number of highly toxic lead salts have colorful names that may tend to conceal
their true and hazardous nature. These names include: salt of Saturn, chrome
yellow, White Lotion, Naples yellow, Verona Yellow, Turner’s Patent Yellow, chrome
red, Paris red, Persian red, Austrian cinnabar, mineral orange or red, and Saturn
Red.
Thus, it is possible to find lead in many forms, in addition to lead-based paint, in
commercial, medical, educational, art studio, and home environments.
Health Effects of Lead Exposure
Lead serves no known beneficial purpose in the human body. The human body
requires other metals in order to function (e.g., iron, zinc, copper). Many scientists
believe the slightest exposure to lead triggers biochemical changes that may have an
adverse effect on various organs of the body. The National Toxicology Program
(NTP) classifies lead acetate (CAS No. 301-04-2) and lead phosphate (CAS No.
7446-27-7) as materials that are reasonably anticipated to be human carcinogens.
Occupational exposure to lead usually occurs through inhalation, the most common
source of lead exposure, or ingestion. Lead can also be absorbed through the skin.
Lead acetate, often used in hair dyes, can be absorbed 1.5 times as fast as other
lead compounds. When lead is present in the air, it can be inhaled and absorbed
through the lungs and upper respiratory tract. Ingestion and absorption through the
digestive system can occur if lead is present on food, cigarettes, or other lead contaminated items placed in the mouth or on the lips. Lead can be consumed when
acidic fluids, such as wine, are stored for long periods in lead crystal decanters.
Electricians have absorbed lead by chewing on plastic insulation materials that
contained lead-based compounds.
When lead enters the body it is distributed initially to the blood, and eventually to soft
tissues (kidneys, liver, nervous system) and bone. Stored lead is excreted from the
body at a very slow rate. Because of this slow rate, exposed individuals who are
removed from lead contaminated environments due to high blood lead levels may
not achieve normal levels for months, possibly years.
The most commonly used measure of internal lead exposure is the concentration of
lead in the blood, denoted as micrograms of lead per deciliter of whole blood. A
microgram is one millionth of a gram, or about one-tenth the weight of a grain of salt. A deciliter is one-tenth of a liter.
The following systems or organs are adversely affected by lead:
- The Nervous System: the nervous system is composed of two major systems,
the central system, which includes the brain and spinal cord, and the peripheral
system, which comprises the nerves extending from the spinal cord. The central
nervous system is the primary target of lead exposure. Symptoms of lead
exposure are; behavior changes, such as irritability and shortened attention
span, suppression of appetite, sleep disturbance, hyperactivity, hearing
impairment, short-term memory loss, and reductions in intelligence. - Blood: when lead is absorbed into the blood it will attach to the red blood cells. Lead interferes with the production of both hemoglobin and red blood cells
resulting in anemia. - Gastrointestinal Tract: the gastrointestinal tract includes the stomach and the
small and large intestines. Since lead can be ingested the gastrointestinal tract
is one of the first target organs encountered. Symptoms include constipation and
acute pain. - Kidneys: the function of the kidneys is to filter substances out of the bloodstream that are harmful to the body. Chronic exposure to lead eventually interferes with the filtering process by altering the metabolism of the kidney. Kidney damage is irreversible and has been recognized as a disease affecting many persons who have worked with lead.
