Simon Cotton takes a look at those compounds that find themselves in the news or relate to our everyday lives

What's this about a child dying after swallowing a bracelet? 

Jarnell Brown, a four-year old American boy, died on 22 February 2006, some days after swallowing a bracelet that was a free gift with a pair of trainers. 

According to the Minnesota state epidemiologist, the bracelet contained lead and when stuck in his stomach the bracelet slowly dissolved in the stomach acid. So Brown died of lead poisoning. Brown reportedly had a blood lead content three times the 'emergency' levels. The 'acute emergency' level is 0.7 μg ml-1, compared with a 'normal' level of less than 0.1 μg ml-1.  

How toxic is lead? 

A child playing

Source: istockphoto

Lead has been mined in Spain since about 1000 BC. The ancient Romans' advanced plumbing was constructed from lead. Unfortunately, the lead pipes slowly dissolved in soft water and the dissolved lead was one source of lead poisoning. Romans would boil old wine or even grape juice in leaden vessels, the resulting concentrated sapa or defrutum tasted sweet. The compound lead ethanoate causes the sweetness, and this used to be known as 'sugar of lead'. Honey would have been so much safer. Lead was used in cosmetics, too.

And lead paint?

Lead-based paints were widely used before the mid-20th century. 'White lead' containing lead carbonate and lead hydroxide was especially popular. Old buildings painted in lead paint are possible sources of lead poisoning, especially when they are being 'restored' - dust formed when the paint is removed can be inhaled, which can be particularly harmful to children. Even today, lead paint can be found on toys imported into the UK, and a child sucking them is in danger.  

Why is lead not put in petrol now? 

Thomas Midgley discovered that tetraethyl lead, [Pb(CH2 CH3)4], prevented knocking in car engines, which allowed the use of high-octane fuels and produced more power from engines. Tetraethyl lead was used worldwide in petrol from the 1920s. Its withdrawal began in the 1970s after it was discovered that tetraethyl lead was toxic, affecting children in particular. For example, it was found that children living near motorways had lower IQs than those living in unpolluted areas. 

Have any famous people been killed by lead poisoning? 

Ludwig van Beethoven is perhaps the most famous victim. Samples of his hair were analysed in 2000 and found to contain levels of lead 100 times above present-day values, though it is not known where the lead came from.  

In 2005 analysis done by scientists at the Argonne National Laboratory US, of fragments of Beethoven's skull detected high levels of lead, which must have been present for many years of his life (unlike lead in his hair, which could have been taken up not long before his death). British chemist John Emsley has suggested that lead, which would enhance the symptoms of porphyria, was a factor in the madness of King George III. 

How does lead poison you? 

Lead interferes with the enzyme δ-aminolaevulinate dehydratase (ALAD), a zinc-binding protein which is important in the biosynthesis of haem by bringing together two 5-aminolaevulinic acid (ALA) molecules to create the pyrrole porphobilinogen. Lead affects the kidneys and the nervous system; it also affects the brain, causing delayed or even reversed development, as well as permanent learning disabilities, and of course death.