Lead

Lead, symbol Pb (Latin plumbum, a lead weight), dense, bluish-gray metallic element that was one of the first known metals. The atomic number of lead is 82; the element is in group 14 (or IVa) of the periodic table. Metallic lead is a soft, malleable, ductile metal. When gently heated it can be forced through annular holes or dies. It has low tensile strength and is a poor conductor of electricity. A freshly cut surface has a bright silvery luster, which quickly turns to the dull, bluish-gray color characteristic of the metal. Lead melts at 328° C (662° F), boils at 1740° C (3164° F), and has a specific gravity of 11.34; the atomic weight of lead is 207.20.

Lead is soluble in nitric acid but is little affected by sulfuric or hydrochloric acids at room temperature. In the presence of air, it slowly reacts with water to form lead hydroxide, which is slightly soluble. Lead is toxic when taken internally; although ordinary water usually contains salts that form a coating on pipes, inhibiting the formation of soluble lead hydroxide, pipes used for carrying drinking water should not contain lead.

Lead occurs naturally in eight isotopic forms, of which four are stable and four radioactive. The stable isotopes, lead-206, lead-207, and lead-208, are, respectively, the end products of the uranium, actinium, and thorium series of radioactive decay; lead-204, also stable, has no natural radioactive precursors

Lead is used in enormous quantities in storage batteries and in sheathing electric cables. Large quantities are used in industry for lining pipes, tanks, and X-ray apparatus. Because of its high density and nuclear properties, lead is used extensively as protective shielding for radioactive material. Among numerous alloys containing a high percentage of lead are solder, type metal, and various bearing metals. A considerable amount of lead is consumed in the form of its compounds, particularly in paints and pigments.

Lead taken internally in any of its forms is highly toxic; the effects are usually felt after it has accumulated in the body over a period of time. The symptoms of lead poisoning are anemia, weakness, constipation, colic, palsy, and often a paralysis of the wrists and ankles. Flaking lead-based paints and toys made from lead compounds are considered serious hazards for children. Children are especially at hazard from lead, even at levels once thought safe. Lead can reduce intelligence, delay motor development, impair memory, and cause hearing problems and troubles in balance. In adults, one lead hazard at levels once thought safe is that of increased blood pressure. Present-day treatment of lead poisoning includes the administration of calcium disodium ethylenediaminetetraacidic acid, or EDTA, a chelating agent; lead is removed from the body by displacing the calcium in EDTA and forming a stable complex that is excreted in the urine.