Introduction

Lead is a soft, blue-gray metal, usually found as lead compounds, combined with other elements. Much of its presence in the environment stems from

• Its historic use in paint and gasoline in the United States,
• Recycling operations,
• Ongoing or historic mining/smelting,
• Commercial operations, and
• Lead contaminated consumer products.

Forms of lead

Elemental lead.

The chemical symbol for lead is Pb (from the Latin name plumbum). Lead has an atomic number of 82 and an atomic weight of 207.2. It is a bluish-grey metal that tarnishes easily in air to a dark grey. The density of lead is 11.34 g/cm3. It has a low melting point of 327.46 °C or 621.43 °F. Naturally occurring lead ores comprise 0.002% (15g/t) of the earth's crust.

Inorganic lead.

This is the form of lead found in higher lead content paint, soil, dust and various consumer products. The color varies, depending on the chemical form, and the most common forms are white lead (a lead carbonate compound), yellow lead (lead chromate, lead monoxide) or red lead (lead tetraoxide). Lead acetate has a sweetish taste.

Organic lead.

Tetraethyl and tetramethyl lead is the form of lead used in leaded gasoline to increase octane rating. The combustion of organic lead when it is added to gasoline as a fuel additive results in the release of lead into the atmosphere. However, their use was phased out in the United States starting in the early 1970's, and banned for use in gasoline for motor vehicles beginning January 1, 1996.

Organic forms of lead are extremely dangerous, as they are absorbed through the skin and are highly toxic to the brain and central nervous system, much more so than inorganic lead.

Exposure to organic lead is generally limited to an occupational context [EPA 1996]. Potential exposures to organic lead should be taken very seriously. The symptoms and treatment are different from those of inorganic lead.

The main focus of this course is on inorganic lead toxicity.

Properties

Lead is a

• Very soft,
• Dense, and
• Ductile (moldable) metal.

Lead is very stable and resistant to corrosion, although acidic water may leach lead out of

• Pipes,
• Fittings, and
• Solder (metal joints).

Lead is a poor conductor of electricity and an effective shield against radiation.

Because of these properties, and because it is relatively easy to mine and recycle, lead has been used for many purposes for thousands of years. Ancient Romans used lead for plumbing, among other uses. In modern times, lead was added to paint and gasoline to improve performance. In the United States, lead was phased out of gasoline starting in the late 1970's, and banned for use in gasoline for motor vehicles beginning January 1, 1996, due to health concerns. Current uses of lead are discussed further in the next section.

Lead accumulation in the body is the result of anthropogenic (human) use, which has concentrated lead throughout the environment. Because lead is spread so widely throughout the environment, it can be found in everyone's body today. The main exposure route is oral, especially in small children, as they have hand-to-mouth behaviors that increase their risks. The respiratory route allows exposure to lead-containing dust, especially in occupational settings and during home renovations. Some authors suggest that because environmental lead accumulation and levels found today, which can result in adverse health effects, many people are exposed to levels of lead that are "orders of magnitude" greater than that of pre-industrial levels [Jusko et al. 2008; Flegal and Smith 1995; Budd et al. 1998].

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