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Abadin H, Ashizawa A, Stevens YW, et al. Toxicological Profile for Lead. Atlanta (GA): Agency for Toxic Substances and Disease Registry (US); 2007 Aug.

Cover of Toxicological Profile for Lead

Toxicological Profile for Lead.

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4CHEMICAL AND PHYSICAL INFORMATION

4.1. CHEMICAL IDENTITY

Lead is a naturally occurring element and is a member of Group 14 (IVA) of the periodic table. Natural lead is a mixture of four stable isotopes, 208Pb (51–53%), 206Pb (23.5– −27%), 207Pb (20.5–23%), and 204Pb (1.35–1.5%). Lead isotopes are the stable decay product of three naturally radioactive elements: 206Pb from uranium, 207Pb from actinium, and 208Pb from thorium.

Lead is not a particularly abundant element, but its ore deposits are readily accessible and widely distributed throughout the world. Its properties, such as corrosion resistance, density, and low melting point, make it a familiar metal in pipes, solder, weights, and storage batteries. The chemical identities of lead and several of its compounds are given in Table 4-1.

Table 4-1. Chemical Identity of Lead and Compounds.

Table 4-1

Chemical Identity of Lead and Compounds.

4.2. PHYSICAL AND CHEMICAL PROPERTIES

Lead exists in three oxidation states: Pb(0), the metal; Pb(II); and Pb(IV). In the environment, lead primarily exists as Pb(II). Pb(IV) is only formed under extremely oxidizing conditions and inorganic Pb(IV) compounds are not found under ordinary environmental conditions. While organolead(II) compounds are known, organolead chemistry is dominated by the tetravalent (+4) oxidation state. Metallic lead, Pb(0) exists in nature, but its occurrence is rare.

Lead’s extensive use is largely due to its low melting point and excellent corrosion resistance in the environment. When exposed to air and water, films of lead sulfate, lead oxides, and lead carbonates are formed; these films act as a protective barrier that slows or halts corrosion of the underlying metal. Lead is amphoteric, forming plumbous and plumbic salts in acid and plumbites and plumbates in alkali. Lead is positioned slightly above hydrogen in the electromotive series and therefore should theoretically replace hydrogen in acids. However, the potential difference is small and the high hydrogen overvoltage prevents replacement (King and Ramachandran 1995; Sutherland and Milner 1990).

Data on the physical and chemical properties of lead and several of its compounds are given in Table 4-2

Table 4-2. Physical and Chemical Properties of Lead and Compounds.

Table 4-2

Physical and Chemical Properties of Lead and Compounds.

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