Cyanide levels in raw sweet cassava varieties and people’s perception on cyanide poisoning in Kagera and Morogoro regions of Tanzania

Abstract

Cassava (Manihot esculenta Crantz), an edible crop that is renowned out of its growth advantages over other crops, carries cyanide which is potentially poisonous to humans. The threat is intensified by human habit of consuming raw cassava tubers whose toxicological status is not established. Cases and indicators of cyanide poisoning due to cassava consumption are evident in Tanzania, particularly in Kagera and Morogoro regions. This study was launched to quantify cyanide in tubers of sweet cassava varieties grown in Kagera and Morogoro regions and thereafter to assess if it is safe for humans to consume raw tubers of sweet cassava varieties grown in the study area. Another objective was to assess whether the habit of consuming raw cassava tubers was out of people’s lack of awareness about cyanide and its poisoning effects or negligence. The study employed cross-sectional research design to collect participants’ responses on cyanide and its associated poisoning effects and to determine cyanide levels in sweet cassava tubers by using alkaline titration method. Sixty six tubers of 12 sweet cassava varieties from the study area were analyzed and 386 participants were involved in the study. The study findings showed that cyanide levels in the raw sweet cassava tubers were above the internationally accepted level in human consumables (10 mg/kg) and thus unfit for human consumption in their raw state. Some sweet varieties were found to be wrongly classified as sweet because their cyanide content was above 50 mg/kg. The inconsistency of cyanide levels in tubers of similar variety showed that a variety can exist in both sweet and bitter forms depending on environmental factors, making the categorization of varieties into sweet and bitter varieties misleading. Furthermore, the habit of consuming raw cassava tubers was found to be mostly cultivated by people’s lack of awareness with regard to the presence of cyanide in cassava tubers (86%) and on cyanide poisoning effects (81%) respectively. It was also found out that the slippery tissue and the inner tissue of the cassava parenchyma differ significantly in cyanide content so that the habit of scratching off the slippery tissue contributes to reduction of cyanide in cassava tubers. This research work recommends that the public should be sensitized on the issue of cyanide in cassava, the poisoning effects it has to human health as well as ways of identifying and dealing with the poison contained in cassava tubers prior to human consumption. Apart from inventing simple, inexpensive and efficient cyanide quantifying devices, genetically modified cassava varieties need be produced and disseminated in which the gene for cyanide expression is either masked or removed as an attempt to protect people against cyanide poisoning.