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Question: What makes lead toxic?
There has been a lot of concern lately about the presence of lead-based paint on toys imported from China, which makes your question particularly relevant. Before discussing the negative effects of lead, I want to emphasize that lead is not always "bad." If you have ever had an x-ray image taken of a part of your body, you were probably covered with a heavy vest of plastic-coated lead to help protect the rest of your body from damage. Lead is also commonly used in car batteries, where it is also enclosed in plastic to prevent direct contact. It is not simply a matter of lead always being something we should fear and avoid but rather knowing how lead can be harmful and making sure to limit that risk.
Lead is an element (a substance made of only one kind of atom) that has been known and used by humans for at least 6000 years. The ancient Romans, for instance, drank out of lead cups and used lead pipes for plumbing. The term "plumber" actually comes from the Latin word for lead, plumbum. This is also why lead is abbreviated on the Periodic Table of the Elements as "Pb" even though the English word "lead" has neither a "p" nor a "b" in it.
The toxic nature of lead has also been know for some time, with records of illnesses suspected to be caused by lead poisoning dating back to 250 BC. Lead has been linked to many different types of health problems, with particularly harmful effects on the brain and nervous system. In order for it to be dangerous, lead has to get into your body in a way that it can be absorbed. For this reason, the plastic-coated lead vests that are used for patients during X-rays and lead-based car batteries are not much cause for concern as long as these are used and disposed of properly. The lead-based paint in children's toys poses a major risk, however, since young children often put toys in their mouths. To make matters worse, the lead compounds (substances made from two or more different atoms) in the paint often have a sweet taste that the children enjoy, which means they will continue to put the toys in their mouths and expose themselves to even more lead.
There is no known need for lead in the human body. The reason that lead is toxic is that its ions (atoms that have an electric charge) interfere with normal body function by taking the place of necessary metal ions (like calcium, iron, and zinc) in proteins. The proteins cannot function correctly when lead is present and this can result in, among other issues, problems thinking clearly or learning new information. Although patients may improve to some extent with treatment, certain effects of lead poisoning appear to be irreversible. This potential for permanent damage is why there is so much concern about lead poisoning in young children, where the brain is still developing, and why it is so important that we, as both individuals and global citizens, understand how to limit everyone's exposure to lead.
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