Fascinating chemicals – arsenic

This week’s fascinating chemical is arsenic (but we’re neglecting old lace for the time being – boom-tish!).

In what would most likely be the most obvious statement of the day, arsenic is a poison.  Because it was so frequently used by would-be rulers to murder their rivals in medieval times, it has been called both the Poison of Kings and the King of Poisons.  The use of arsenic for murder became much less effective, however, after a British chemist named James Marsh developed a test in 1836 that could accurately detect the presence and quantity of arsenic in a tissue sample.  In fact, this was actually the first documented use of forensic toxicology in a criminal case!

Historically, arsenic has also many other, non-murderous uses, including cosmetics, in Emerald Green pigment and as a food colouring for sweets in the 1800’s.  The toxicity of arsenic was one of the reasons that it was used in flypaper and rat baits and also for treating wood, until we came up with synthetic pesticides in more recent times.  Naturally, its toxicity towards humans meant that the use of arsenic has been almost completely banned.  However, a particular arsenic compound called roxarsone is still being used in chickens to prevent disease! I doubt that the levels are anything to worry about but it was a bit of a surprise.

The way that arsenic causes its lethal effects is highly complicated, but essentially it disrupts the internal energy systems of the cell, causing the cells to eventually die off.  Some of the symptoms of arsenic poisoning include headaches, nausea, diarrhoea, vomiting, painful convulsions and cramps, dehydration and weakness.  One reason why arsenic was considered to be such an effective poison is because several of these symptoms would also occur in someone suffering from cholera, so until the Marsh test was developed arsenic poisoning could more or less go undetected.  A more characteristic symptom that can point to chronic arsenic poisoning is the presence of horizontal white lines on the fingernail called Mees’ lines.

So a fascinating poison with a long history – keep the suggestions coming!

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