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What Makes Lead Poisonous?


Lead is a heavy metal that is bluish-white when freshly cut, but tarnishes to a dull gray.

Lead is a heavy metal that is bluish-white when freshly cut, but tarnishes to a dull gray upon exposure to air. The pure metal is used for radioactive shielding, among other purposes.

L. Chang, wikipedia.org
Question: What Makes Lead Poisonous?
Most people are aware that lead is a poison. It's also a very useful metal. People have been using lead in their daily lives for a long time. The Romans made pewter dishes and pipes for water from lead. The effects of poisoning from lead leeching into liquids probably contributed to the fall of the Roman Empire. Lead exposure didn't end when lead-based paint and leaded gasoline were phased out. Lead is found in the insulation coating electronics, leaded crystal, storage batteries, to coat the wicks of some candles, to stabilize certain plastics, and in solder. You are exposed to trace amounts of lead every day.
Answer: You know lead is toxic, but do you know what makes it poisonous? In a nutshell, it's toxic mainly because it preferentially replaces other metals (e.g., zinc, calcium and iron) in biochemical reactions. Lead interferes with the proteins that cause certain genes to turn on and off by displacing other metals in the molecules. This changes the shape of the protein molecule such that it can't perform its function. Research is ongoing to identify which molecules bind with lead. Some of the proteins that are known to be affected by lead regulate blood pressure (which can cause development delays in children and high blood pressure in adults), heme production (which can lead to anemia), and sperm production (possibly implicating lead in infertility). Lead displaces calcium in the reactions that transmit electrical impulses in the brain, which is another way of saying it diminishes your ability to think or recall information, or makes you stupid.

Paracelsus' idea that the dose makes the poison doesn't really apply with lead. Many substances are non-toxic or even essential in trace amounts, yet poisonous in quantity. You need iron to transport oxygen in your red blood cells, yet too much iron can kill you. You breathe oxygen, yet again, too much is lethal. Lead isn't like those elements. It's simply poisonous. The main concern is lead exposure with small children, because lead can cause developmental problems, plus kids engage in activities that increase their exposure to the metal (e.g., putting things in their mouths, not washing their hands). There is no minimum safe exposure limit, in part because lead accumulates in the body. There are government regulations regarding 'acceptable' limits for products and pollution, because lead is useful and necessary, but the reality is, any lead is too much lead.

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