Effect of GarriI processing effluents [waste water] on the cyanide level of some root tubers commonly consumed in the South East of Nigeria

Abstract

Root tubers are the important staple food crops in the tropics, Nigeria inclusive. In the South East of Nigeria, the major staple root tuber crops include Dioscorea rotundata, (White yam) Dioscorea alata, (Water yam) Xanthosoma sagittifolium, (Red Cocoyam) Colocasia esculenta, (White Cocoyam) Ipomea batatas (Sweet potato) and Dioscorea dumetorum (Domestic yam). Due to inadequacies in supply, these tubers are always in high demand by consumers. To make up for the high demand, peasant farmers cultivate these tubers in any available space around homes. Around most homes in the villages are garri (cassava flour) processing factories, with the effluents (waste water) allowed to flow into adjoining farmlands without any form of treatment. It has been reported that cassava tubers and their effluents contain high concentrations of cyanide, thus the cyanide in the effluent may be adsorbed by the soil onto which it is disposed. Plants that are grown on soil of low potassium content and high nitrogen content have been reported to have high hydrocyanic acid concentration in their tubers. Numerous studies have described environmental exposure of humans to cyanide in African populations. Little is known about exposure to cyanide toxins from processed or unprocessed root tubers commonly consumed in Africa; and data on the food concentration of cyanide which is a potential poison and systemic toxicant is scanty. This study determined the concentrations of cyanide in some root tubers grown in a cassava processing plant effluent [waste water] contaminated farm land and commonly consumed in South East of Nigeria. Dioscorea rotundata had 10.13±1.9mgHCN/kg, while Dioscorea alata had 9.12±0.93mgHCN/kg. Xanthosoma sagittifolium and Colocasia esculenta were found to have values of 15.19±1.69mgHCN/kg and 11.81±1.19mgHCN/kg, respectively. Ipomea batatas [red cultivar] had cyanide level of 8.44±1.20 mgHCN/kg, while the white cultivar had 8.44±1.20mgHCN/kg. Dioscorea dumetorum [domestic] showed cyanide level of 35.44±1.69mgHCN/kg. These values are significantly [p<0.05] higher compared to values from the control site for the same cultivars, 9.65±1.36mgHCN/kg, 8.45±1.60mgHCN/kg, 14.77±1.33mgHCN/kg and 10.89±1.55 mgHCN/kg, respectively while I. batatas and D. dumetorum had 7.26±1.34mgHCN/kg, 32.76±0.05mgHCN/kg, respectively. The difference in cyanide content between cultivars from the assumed contaminated site and control site could be as a result of environmental factors, like temperature, humidity, altitude and possibly the cassava effluent [waste water]. This preliminary study highlights the need to study the toxicological implications of chronic low–level exposure to cyanide from African root tubers as a result of poor waste disposal methods.

Keywords: Tubers, cyanide, toxicity, soil, contamination

African Journal of Food, Agriculture, Nutrition and Development, Volume 12 No. 6