Lead
Lead is a metal element denoted by the atomic number 82. Its atomic symbol, Pb, comes from the Latin word plumbum. It is a very soft, highly malleable metal with a bluish-white sheen that tarnishes rapidly to a dull gray. It has an atomic weight of 207.2, a melting point of 621.43°F (327.46°C), and a boiling point of 3180.2°F (1749°C). Lead is primarily found in galena and is often mixed with copper and zinc.
Lead has been in use as a metal since very early times. Lead artifacts from 3800 b.c. still exist. Its softness and relatively low melting point made it an easy metal for ancient technology to work. The Egyptians may have learned to use it as early as 5000 b.c. Among other uses, the Egyptians used a lead oxide, called red lead, as a cosmetic pigment. The Romans used lead for pipes. Alchemists believed lead was the oldest metal in existence and thought it was associated with the planet Saturn.
Modern uses for lead include plumbing as well as ammunition (bullets) and storage battery plates. Radiation shields are made of lead, since it is able to absorb gamma ray. When alloyed with tin, lead can be used as solder. It resists corrosion and is used in numerous industrial capacities. It is used in a substance called tetraethyl, an antiknocking agent added to gasoline, as a base for paints and as an ingredient in insecticides. Lead oxides are used to produce lenses with high refractive indices. Due to environmental concerns, scientists have generally tried to reduce the use of lead.
Lead, for all of its uses, can be dangerous. Over time, it may accumulate in the bodies of humans and animals. The result of both long-term accumulation and a short-term large dosage is the same. Known as plumbism, or lead poisoning, its moderate effects can include lethargy and muscle weakness. Ultimately, it can lead to permanent paralysis and brain damage. The dangers of lead have been known for centuries. Physicians in the Roman Empire correctly diagnosed plumbism as resulting from drinking water carried in pipes of pure lead or eating from dishes which contained lead. Their recommendations included using baked clay for water systems and substituting other materials in dishes; however, their advice was often ignored.
In more recent times as well, the poisonous effects of lead were recognized as an industrial hazard years before anything was done about it. A leader in combating overexposure to lead in factory work was the American toxicologist Alice Hamilton (1869-1970). During the early 1910s, she did extensive research on workers who had been exposed to lead in their occupations. Much of her work had to be done in the back rooms of taverns and barber shops since the workers feared the loss of their jobs for cooperating. Europe, with its socialized industries, had already taken measures to protect its workers from industrial poisoning. However, American industrialists were generally unwilling to invest money in safety precautions. Gradually, Alice Hamilton was able to use her research to convince the employers to make the necessary changes.
The problems with lead did not go away with Hamilton's work. The accumulations of automobile pollutants in the atmosphere contained traces of lead. For years, petroleum companies had added a lead compound to their gasolines in order to make car engines run more smoothly. During the 1960s, an effort was begun to rid gasolines of their lead additives. Over a thirty-year period, leaded gasolines have been nearly phased out as new automobiles capable of using lead-free gasoline have replaced the old ones that could not. Traces of lead are often found in tap water, coming from old lead pipes and soldered joints containing lead.
Lead poisoning is still a major problem with small children, especially in poorer households. Old pipes and old lead-based paint in inexpensive housing are the main reasons. As leaded paint peels from walls for lack of maintenance, children may pick it and put it in their mouths. The lead in the paint remains in the child's body and can lead to physical lethargy and mental retardation.
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