From Stars To Stalagmites: How Everything Connects by Braterman Paul S

Author:Braterman, Paul S.
Language: eng
Format: epub
ISBN: 9789814324984
Publisher: World Scientific Publishing Company
Published: 2012-05-10T16:00:00+00:00

The Poisonous Metals; Arsenic, Mercury, Lead

We have already met arsenic as an essential but accidental component of early bronze. It commonly occurs combined with sulphur, and sometimes another metal. Heating these in air converts the sulphur to sulphur dioxide and the arsenic to its own oxide, which is easily reduced by charcoal or other sources of carbon. The main source is the mineral arsenopyrite, FeAsS. This when heated decomposes to give the iron sulphide FeS, while the arsenic is given off as a vapour, which condenses in the chimney of the reaction vessel. The alchemists knew that blending arsenic with copper gave a white alloy, resembling silver, a noble metal and perhaps, in their minds, already on the way to being converted to gold.

Arsenic28 forms alloys with many metals, and small amounts are added to brass plumbers’ fittings to increase their chemical inertness, and to harden the lead plates in car batteries. It was formerly used in solder, leading to poisoning by moonshine which leached it out of joints in the still. The compound gallium arsenide is a semiconductor with uses in electronics, and the more common silicon-based electronics rely on the controlled addition of arsenic to generate electron-rich conducting pathways.

White arsenic, As2O3, was used in 18th century wig powder (where it must have been very effective against embarrassing personal vermin) and in the next century Victorian women used it in makeup, and even ate it (in small amounts!) to produce a pallid complexion. It was well known as a poison, useful for ants, rats and mice, unwanted spouses, and even royalty. Nero is said to have used it to get rid of his more popular younger brother Britannicus, and Cardinal Ferdinando de’ Medici almost certainly29 used arsenic to get rid of his own inconvenient brother, Francesco, Duke of Tuscany. The much-married Lucrezia Borgia (daughter of Pope Alexander VI) was also accused of arsenic poisoning, among other lurid crimes, but this information comes from politically biased sources and may just be Renaissance tabloid gossip. Be that as it may, family use declined after 1840, when the newly developed Marsh test30 was successfully used to prove that Mme LaFarge had indeed poisoned her husband. Suggestions that Napoleon was deliberately poisoned with arsenic do not stand up to examination. He will have been exposed to arsenic from the Paris Green (copper arsenoacetate) pigment then widely used for wallpaper, but the large and highly variable amounts present in hair samples seem to have come from the subsequent use of arsenic-containing preservatives.31 Chronic arsenic poisoning by contaminated groundwater is, however, a serious problem in many parts of the world, in particular Bangladesh.32

One group of arsenic compounds, arsenates, shows a chemistry very similar to that of phosphates, and phosphates play an essential role in life, not least in providing the backbone linkages of DNA and RNA. Arsenic is poisonous because it gets caught up in the same metabolic cycles as phosphorus, but the arsenic-containing molecules react with water and fall apart before they can do their job.

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