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Metals
    T he Beatles made an enormous splash in Liverpool. But as big as they were, there was one commodity that was much bigger and much more controversial.
    Liverpool is a port city. So ships come and go, carrying coal, timber, grains, steel, crude oil, and endless other commodities. Loaded onto ships leaving Liverpool in the eighteenth century was the most controversial product in English history.
    In their holds were bars of copper—that ordinary reddish metal that makes a pot or pan look so shiny and bright. Copper looks innocent enough. But it was the currency of the British slave trade.
    The ships sailed from Liverpool to West Africa, where copper and brassware were exchanged for slaves who were then carried across the Atlantic to the Americas. There the human cargo was off-loaded, and rum and sugar from slave plantations were carried back to Britain. This triangular trade route from Britainto Africa to the Americas and back was fueled by copper from Liverpool. It was what African slaveholders wanted.
    Copper also kept the ships afloat. Sailing around the North Atlantic, wooden ships worked out well. But as slave ships entered the Caribbean, they encountered a tiny mollusk, called
Teredo navalis,
which feeds on wood. Or, more accurately, these mollusks have a special organ that carries a bacterium that digests cellulose, dissolving the hulls of ships. A few too many mollusks and your ship is on the ocean bottom.
    The answer was to sheathe the hulls in copper. Copper kept the mollusks out, the hulls intact, and the slave ships sailing.
    Many Britons called for an end to the slave trade. But copper merchants protested vigorously. They were not getting rich selling pots and pans in Lancashire. The slave trade was the market they wanted to protect. Finally, in 1807, public sentiment turned, and it became illegal for British subjects to traffic in slaves. In 1833, slavery was abolished in all British colonies.

Metals in the Brain
    Metals always seem to come in the form of double-edged swords. Lead gave us pipes for plumbing, but it has also poisoned countless children. Mercury gave us thermometers and electrical switches, but it also caused birth defects. Metals build bridges and locomotives, and also bullets, prison cells, and hand grenades.
    Metals are a double-edged sword within the human brain, too. In the last chapter, we saw that researchers have found
plaques
and
tangles
within the brains of people with Alzheimer’s disease. If you were to analyze a typical plaque—one of the small deposits that are found among the brain cells—you would discover that much of it consists of
beta-amyloid
protein. But there is something else there, too. Teasing the plaques apart, researchers have found traces of copper. They have found other metals, too, particularly iron and zinc, and perhaps others, as well. 1
    All three of these metals are needed by the body—copper for building enzymes, iron for blood cells, and zinc for nerve transmission, among many other functions. You get them in the foods you eat. But it turns out that if you get too much of any of them, they can damage your brain cells. The difference between a safe amount and a toxic amount is surprisingly small. And that is exactly the problem.
    Iron and copper are unstable. Just pour a little water into a cast-iron pan and let it sit for a bit. The rust you see is oxidation. Copper oxidizes, too, which is why a bright shiny penny soon darkens, sometimes combining with other elements and turning green.
    Pretty colors, yes. What is not so pretty is when these chemical reactions happen inside your body. That’s when iron and copper spark the production of
free radicals—
highly unstable and destructive oxygen molecules that can damage your brain cells and accelerate the aging process. 2 In a nutshell, iron and copper cause free radicals to form, and those free radicals are like torpedoes attacking your cells.
    So, am I saying that memory problems might be caused by