Cassava's nasty after-taste

The importance of cassava in many people s diets can not be underestimated, nor should the effects of the sometimes fatally high levels of cyanide in cassava. One example is Konzo, a permanent paralytic condition of the legs which mainly affects children and young women in central and eastern Africa. In periods of drought, cyanide levels in cassava are higher than usual, and in periods of crisis and war, the variety of diets decreases and people rely more heavily on cassava because requires less inputs and attention. Konzo is also endemic in some areas. In West Africa the condition TAN (tropical ataxic neuropathy) is more common. It is a sensory disease, leading to difficulties in walking, numbness, deafness and blindness. There is no cure for Konzo but it can be avoided by reducing cyanide intake from cassava. One way is to partially substitute cassava with other crops in the diet. Improved processing is another: traditional methods such as sun drying and heap fermentation leave a lot of cyanide in the cassava flour. Introducing varieties with low cyanide contents is another possible solution; and all these methods can be combined. How can you measure cyanide levels in cassava plants and products and thiocyanate levels in urine (see Spore 88) and thus predict Konzo? At the Australian National University Dr J Bradbury has developed simple measuring kits, available free of charge on request. Many African cassava varieties are bitter and high in cyanide levels; this trait is also useful, in that it deters vermin. In the Pacific, where sweet varieties are grown, there is no cyanide problem. [caption to illustration] Excessive cynanide in cassava can cause localised paralysis. It can be avoided, not cured, but therapy helps, as in Nampula province, Mozambique. J H Bradbury, School of Botany and Zoology ANU, Canberra, ACT 0020, Australia Fax: +61 2 61 25 55 73 Email: Howard.Bradbury@anu.edu.au Website: www.anu.edu.au/BoZo/CCDN/