Assessment of Some Toxic Metal Concentrations in Selected Ready-to-use Medicinal Plant Roots and Stem Barks in Ibadan, Nigeria

The aim of this study is to assess the concentrations of selected toxic metals (Cr, Ni, Cu, Zn and Cd) in some herbal plants sold in 3 markets within Ibadan, Nigeria. Sampling was done on a daily basis for 7 days in 2012. Blended plant samples were heated at 550ºC for 4 hours and digested using 2M HNO3. The extracts were subjected to Flame Atomic Absorption Spectrometry (FAAS) to determine their toxic metal concentrations. Metal recovery study was used to validate the analytical method. The concentration of Cu ranged from 0.04mg/kg in Olax subscorpioidea to 9.44mg/kg in Adansonia digitalia. For Zn, the concentration was lowest (0.94mg/kg) and highest (35.40mg/kg) in Senna podocarpa and Kigelia Africana respectively. Pb concentration ranged from 1.6mg/kg in Adansonia digitalia to 6.15mg/kg in Sphenocentrum jollyanum. Cr, Cd and Ni levels were below the detection limits [Cr (0.04mg/L), Cd (0.01mg/L) and Ni (0.10mg/L] of the spectrophotometer used. The mean Zn (8.04mg/kg) and Cu (1.80mg/kg) concentrations in the plants were above the World Health Organization (WHO) limits for Cu (0.3-1.0mg/kg) and Zn (0.05-0.5mg/kg) respectively in the plant roots and stem barks. Spearman partial correlation showed variation in selected trace metal (Cu and Zn) concentrations in the plant samples. Recovery study for Zn in Bridelia ferruginea and Adansonia digitalia were (94.85%) and (101.40%) respectively. On the average, the concentrations of toxic metals in the herbal plants studied were within WHO acceptable limits.