Science
Gin trap
Bernard Dixon
Some of the most intriguing detective stories of medical science these days concern not simply technical experimentation in the laboratory, but a broader geographical approach that attempts to relate disease patterns to environmental and social factors. Methuen have now published a textbook, Medical Geography, to mark the fact, edited by Dr Neil McGlashan, a geographer at the University of Tasmania.
Take, for example, the striking variations in the incidence of oesophageal (gullet) cancer in different parts of Africa. Some years ago, Dr A. G. Oettle showed that even south of the Sahara, the distribution of this type of cancer was extremely patchy. In his report he mentioned the possibility.that lead or another metal was responsible.
The first breakthrough came when Dr R. J. W. Burrell plotted the homes of oesophageal cancer victims on a large map of localities where the disease was relatively common. A marked clustering effect was immediately obvious, with the patients' homes scattered around shebeens — stores of illicitly prepared spirits.
Many difficulties attended this and later work in pinpointing precisely the cause of the clustering. One stemmed from the period taken for the cancer to develop. Another was the reluctance of victims in some parts of Africa to seek treatment.
Faced with such problems, Dr McGlashan and a team from the University of Zambia initiated a survey in central Africa designed to gather hard statistics about the relationship of oesophageal cancer to environmental and social factors. During their 8,000-mile journey, a clear correlation began to emerge between the cancer and consumption of the illicit liquor known as kachasu or Malawi gin, and the team collected samples for testing later. At the end of the survey, statistically significant correlation was amply confirmed.
Kachasu is distilled from a beverage of maize, maizecobs, and sugar. The crude equipment used for the job is usually knocked up from old metallic containers, with bicycle frames and discarded exhaust pipes as condensers. Analysis revealed wide variations
in the composition of the spirits, but the better quality preparations contained up to 30 per cent of alcohol. Some samples contained high levels of zinc and copper. Metal contamination could, therefore, account for the cancer. This hypothesis, however, was short-lived. Visits to parts of Zambia where oesophageal cancer was rare showed that local alcoholic drinks were just as contaminated with copper or zinc.
Then came the crucial news. Chemists at the British Manufacturing Industries Research AS sociation at Leatherhead detected small amounts of a cancer-causing substance, DMN, in the earlier Zambian samples. Next, a survey, sponsored by the Medical Research Council, further afield (including Ghana, Eire, Canada, and Yugoslavia) showed that wherever spirits were prepared bY illegal distillation, necessitating secrecy and crude methods, the final product contained DMN. Bat where precisely did it come froin? The,investigators returned to Kenya, where they had found the highest concentrations of DMN iii any of the samples, and tested the separate ingredients used at each stage of the manufacturing process. The result — DMN was absent from all the starting materials but appeared during fermentation, probably as a result, of the activity of 'wild yeast5 which, in dirty conditions, can easily contaminate a fermentation Another piece of the jigsaw came from a visit to the Mazary daran province of Northern Ira° to investigate the high incidence of oesophageal cancer there, PO: ticularly among women. In this devout Muslim area, alcohol could not be responsible for the cancer. But the research team found DMN in grape vinegar (made by fer,, mentation); pickles prepared us1°6 the vinegar; and anarteen, a angture, taken to relieve digestive discomfort during pregnancy.. Finally, there are good tidings from Dr McGlashan's ancillary, research. Commercially prepare,'" spirits are free of DMN. Scotcn whisky, 'exhaustively tested, contains not a trace of the stuff.
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