Oral acute toxicity study of selected botanical pesticide plants used by subsistence farmers around the Lake Victoria Basin

Abstract

A survey carried out around the Lake Victoria region showed evidence that people around this region use plant extracts, parts and powders to protect stored food commodities from insect pests. The widely used plants were identified and selected for biosafety assessments namely: Ocimum gratissimum, Tithonia diversifolia, Eucalyptus saligna, Eucalyptus globulus and Cupressus lusitanica. Wistar mice were acclimatized and divided into groups of six. Each mice group was administered with one extract at different concentrations. The extracts were administered orally and the animals were observed for 24 h. A control group was kept which received only the carrier substance orally. The LD50 values were determined by the use of the graphical method and regression analysis. Oral acute toxicity studies established the LD50 values for essential oils of O. gratissimum, E. saligna and C. lusitanica as 4.570, 2.290, and 3.311 mg/kg, respectively. For ethanol extracts, LD50 values were 12.882, 12.302, 14.996 and 11.481 mg/kg for O. gratissimum, E. globulus, C. lusitanica and T. diversifolia, respectively. For the aqueous extracts, the LD50 of T. diversifolia was found to be 12.302 mg/kg. For E. globulus and C. lusitanica, their aqueous LD50s were beyond 15.000 mg/kg. The oral acute toxicity tests showed weak toxicities for all the plant extracts investigated in the study. The low toxicity levels exhibited by these extracts may be the reason why these plant products have been used by local communities for long without adverse effects. Chronic studies should be carried out to assess whether these extracts have serious effects on experimental animals exposed to them at small doses for a long period of time.

Key words: Oral acute toxicity, biopesticide, plant extracts, Lake Victoria Basin.