Effect of Cassava Processing Effluents on Antioxidant Enzyme Activities in Allium cepa   L.

The underlying principle of the biomarker approach is to analyse the physiological and/or biochemical response of an organism exposed to an environmental pollutant. Onion bulbs were exposed directly in 0%, 0.2%, 0.4%, 0.8% 1%, 2%, 3%, 4% and 5% concentrations (v/v) to each effluent of three popular Nigerian cassava meals: garri, lafun and akpu for 96 hours. The root growth of the onion bulb and superoxide dismutase (SOD), and catalase (CAT), activities were measured. At 96 h, the root tips showed concentration-dependent growth retardation in all the effluents with EC₅₀ values of 1.5%, 2.5% and 3.5% for garri, lafun and akpu effluents respectively while total phytotoxic effects was induced at higher effluent concentration. The physico-chemical analyses showed that the effluents were highly acidic and contained significant (p<0.05) amounts of cyanide and heavy metals compared to the control. The effluents induced increased malondialdehyde (MDA) levels and accelerated SOD activity at low concentrations but decreased after attaining maximum activity in garri effluent at 1%. Catalase was inconsistent; however, a drastic decrease in activity was recorded at the same effluent concentration. Lafun and akpu induced similar increases in antioxidant enzymic activity up till 2% effluent concentration after which steep decline set in.

Keywords
Processed cassava effluents; Cyanide; Onion bulbs; Allium cepa; Antioxidative enzymes