Arsenic in the air

So what was the toxic vapour given off by wallpaper decorated with a green arsenic pigment? The Victorian chemists knew of one deadly arsenic gas and that was arsine in which three hydrogen atoms were bonded to the element (AsH3), and that they could make this by treating a solution of arsenic trioxide with zinc and sulphuric acid. The German chemist A. F. Gehlen (1775-1815) discovered how dangerous arsine could be when he made some in 1815. Within an hour of sniffing the gas he became ill, displaying symptoms of vomiting and shivering. He took to his bed but became more and more ill and died nine days later. This gas had first been made in 1775 by Scheele but he had avoided breathing it and so chemists had been unaware of its toxicity until Gehlen's accident.

Industrial accidents have been caused by the release of arsine when metal alloys containing arsenic have been treated with acid. The gas can be given off from zinc dross, and in Yugoslavia in 1978 a gang of eight men who were handling this while it was raining were overcome by it. The rain reacted with the dross to release arsine which affected them, and the men had to be rushed to hospital where one of them died. Arsine gas has a special affinity for the haemoglobin of red blood cells and this is what makes it so dangerous. It could even be formed inside lead accumulators, the electrodes of which were made of lead plates alloyed with a little arsenic to strengthen them, and these were used inside the storage batteries of British submarines in World War I. The batteries were sealed units but on board one submarine there was an escape of arsine gas and the crew of 30 men were all exposed to the same concentration of this dangerous gas for the same length of time. Yet they did not all react in the same manner and it was this that made the incident interesting from a medical point of view. One man was not affected in any way. Seven men suffered anaemia and jaundice and were hospitalized, while the rest showed symptoms of anoxemia (abnormally low levels of oxygen in the blood), although not to the extent that they required hospital treatment.

However, arsine was not the gas given off by Victorian wallpaper. Chemists at the time knew there was no possible way in which it could be generated because to do so it would require a chemical reaction between arsenite ions in the dyes and a strong reducing agent. But chemists did know of other arsenic compounds that were quite volatile, and potentially dangerous on this account, such as cacodyl. Dr Frazer was nearly right.

In May 1891 an Italian chemist, Bartolomeo Gosio (1865-1944) started a year-long research project with the intention of proving that arsenic dyes could be a health hazard because they gave off a poisonous gas. Gosio's research was motivated by a problem that had been worrying the Italian authorities for many years: the large number of young children who were sickening and dying of inexplicable causes. They too were aware that doctors were sure that arsenical pigments were to blame and decided something must be done. Gosio's technique was to grow various micro-organisms on a mixture of mashed potato containing a little arsenic trioxide and he simply placed samples in damp cellars where indeed colonies of bacteria and fungi quickly grew on them and produced a garlic odour. Some research was also done by adding Scheele's green and emerald green to the culture medium and then growing the common bread mould on it and again the same smell developed. When he took some of the mould from a piece of rotten paper Gosio noted that the intensity of arsenical gas was such as to be dangerous, and indeed a rat exposed to the vapour quickly died, and a small mouse put in a vessel with the fungus expired within a minute.

Others were also experimenting with microorganisms and arsenical materials and with contradictory results. In 1893 Charles R. Sanger of the Washington University of St Louis, in the USA, did a study of 20 cases in which the poisoning was attributed to wallpaper and showed that indeed this was the cause: the wallpapers all containing arsenic, with the ranges being from 15 to 600 mg/m2. Sanger even noted that the less arsenic in the paper, the more severe was the poisoning and suggested that when the level of arsenic was very high it was too toxic for the moulds to grow. While Sanger in the USA was able to confirm Gosio's findings in 1893, the German biologist Otto Emmerling could not and in 1897 he published a paper saying that he found no arsenical gas given off with his cultures. This was not really a contradiction of Gosio's findings because he had used different microorganisms which were unable to make methyl arsenic and release it into the air.

No one really doubted that Gosio had discovered the reason why there was so much ill health among those living in houses whose walls were decorated with arsenical paints and wallpapers. His findings were such that the sickness associated with breathing the air in such rooms began to be called Gosio's disease. Now it was possible for doctors not only to diagnose the condition but also to treat those affected by removing them from the cause and advising that the room be treated rather than the patient. Nevertheless it took many years before Gosio's disease disappeared. Microbes found damp wallpaper a fertile place to grow. In those days fresh wall plaster was sealed with gelatine (known as size) prior to being painted or wallpapered and the latter was generally stuck on the wall with a flour-based paste. This combination of proteins and carbohydrates made an ideal nutrient for the microbes, especially when it was damp. As the microbes grew they needed to remove the arsenic from their environment and this they did by converting it to the compound trimethylarsine.

As late as 1932 two children in a house in the Forest of Dean on the English-Welsh border died of Gosio's disease. It was only then that an English chemist Frederick Challenger (1887-1983), who was professor of organic chemistry at the University of Leeds and who researched the biological methylation of arsenic, correctly identified trimethylarsine as the cause. This compound had first been made in 1854 when it was shown to be a colourless, oily liquid with a boiling point of 52°C. Improbably as it appeared at the time, we now know that there are enzymes capable of replacing the three oxygen atoms attached to the arsenic in Scheele's green with three methyl groups.

Although trimethylarsine had been identified as the deadly vapour in the 1930s, it was not until 1971 that it was finally revealed how microorganisms could add methyl groups to arsenic. Many microbes can perform this little trick, including two kinds of wood-rotting fungi that can grow on wood treated with arsenical preservatives, although 63 other wood-rotting fungi were unable to do so. Natural gas also contains traces of trimethylarsine, a fact only discovered when technicians working on a gas pipeline in California in 1989 discovered an inlet pipe choked with a deposit which turned out to be pure arsenic. Further research showed that natural gas could contain as much as 1 ^g of arsenic per litre and that this was mainly as trimethylarsine.

There was a strange case of arsenic poisoning in the US Embassy in Rome in the 1950s when Clare Boothe Luce, the US Ambassador to Italy, had to resign because of her illness. It was obvious that she had been poisoned, but by whom? Was it by agents of the USSR? This was at a time when the Italian Communist Party was particularly powerful. So serious might have been the repercussion that the CIA sent a team to Rome to investigate. Eventually the source of arsenic was traced. Booth Luce slept in a room that had not previously been a bedroom and which had a decorated ceiling that contained a lot of arsenic pigments. Was this yet another example of Gosio's disease? In fact it wasn't. On the floor above was a washing machine that made the floor vibrate; this caused the room to become loaded with arsenic-laden dust and it was this which she breathed in and which caused the unpleasant symptoms.

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