Toxic Treasure

By Voynick, Steve | The World and I, November 1999 | Go to article overview
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Toxic Treasure

Voynick, Steve, The World and I

Versatile but potentially poisonous in the blood, lead is a metal whose use for industrial purposes is surging even as we have restricted its use in paints, pipes, gasoline, bird shot, and tin can solders.

During the first half of this century, industrialized nations put huge amounts of lead and lead compounds into everything from paint and gasoline to food cans, water pipes, and ceramic glazes. Then, after discovering that lead poisoning was affecting millions of people, those same nations have spent the second half of the century trying to get the lead out.

And they have been remarkably successful. U.S. Environmental Protection Agency (EPA) administrator Carol Browner calls the effort to reduce lead poisoningin the country "a great American success story of environmental and public health protection." Health and Human Services (HHS) Secretary Donna Shalala considers it "a public health achievement of the first importance."

Yet lead is still a major public health threat. Although we have dramatically reduced the lead-poisoning rate, both the EPA and HHS continue to cite it as the most serious environmental health hazard facing our children. Their data show that far more children are affected by lead poisoning than radon, pesticides, and asbestos combined. Children on Medicaid, in particular, have a much higher risk of lead poisoning because they tend to live in older housing where they are exposed to peeling lead-based paint or to other discontinued uses of lead.

Paradoxically, even though the metal's potential toxicity is well publicized, we use more lead today than ever before in a broad array of products that affect many aspects of our daily lives. Toxic or not, lead seems to be a metal we can't do without.

A metal from antiquity

Along with gold and copper [see "A Metal for All Ages," The World & I, November 1998, p. 182], lead was among the first metals utilized by man. Although it lacks the beauty of gold and the hardness and strength of copper, lead has many other desirable attributes. Soft, dense, and malleable, lead is relatively abundant, eminently workable, largely impervious to corrosion, and easily smelted from its ores. Lead was too soft to be a useful component of tools and weapons, so few ancient lead artifacts exist.

Lead is found occasionally as a native metal, but it occurs most often as lead sulfide (PbS), which is the mineral galena. In ancient times, the heat from wildfires sometimes converted rich outcrops of galena in the presence of organic debris first to an oxide then to metallic lead- -a natural smelting process that early metallurgists replicated in simple furnaces.

Knowledge gained from working with lead sped the development of metallurgy and metal-working methods. Taking advantage of its low melting point of 662 * F (328 * C)--only one-third that of copper or gold--early metalworkers poured molten lead into thin layers that hardened to form sheets used as roofing, floor tiles, and, when rolled into cylinders, pipe sections. The world's first solder, molten lead quickly sealed lead pipe seams and joined pipe sections together into long, leakproof water pipelines. Roman metalworkers fabricated thousands of miles of lead pipe to build elaborate residential plumbing and regional water supply systems. Romans also used lead to make food containers and table utensils, and as a bearing metal for shafts and axles of grinding and wagon wheels--the precursor of the modern practice of using soft metals to reduce the friction of bearings. Fittingly, the chemical symbol for lead, Pb, and the English words plumbing and plumber, all stem from plumbum, the Latin word for lead.

The use of lead raised the Roman standard of living but also provided history's first great lesson about the metal's toxicity. Some medical researchers believe that the lead content of many Roman bones indicates blood-lead levels as high as 75 micrograms per deciliter--three times higher than levels today considered toxic for adults.

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