Evaluation of Potentially Toxic Metal Contamination of Local Medicinal Plants and Extracts Sold in Ibadan, Nigeria

BACKGROUND. Extracts from medicinal plants have been widely used in the treatment of public health ailments, however, medicinal plants may be grown in polluted soil/water environments. Many of these plants are harvested and processed by local and illiterate natural healers and other vendors in an unhygienic manner. This results in the possibility of contamination with potentially toxic metals from the environment. OBJECTIVES. This study evaluated the concentrations of lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu) and zinc (Zn) in 25 samples of different medicinal plants procured from stores in open markets in Ibadan, Nigeria. METHODS. After procurement, the samples were air dried, pulverized and dry ashed. All ashes were dissolved with dilute acid solutions, filtered and the filtrates were stored for metal analysis. Samples with elevated metal concentrations were extracted with water and alcohol solutions to mimic the medicinal extracts obtained from these plants. Metal concentrations were analysed in all extracts and filtrates using atomic absorption spectrophotometry. RESULTS. Metal concentrations (mg/kg dry weight) in all samples ranged as follows: Cu, 0.04 - 9.44; Zn, 0.36 – 35.4 and Pb, below detection limits (BDL) – 6.15. The concentrations of Cd, Cr and Ni in all samples were BDL. The concentrations of all metals in the samples were within accepted limits set for medicinal plants according to international regulatory bodies. All ethanol extracts and 1 out of 4 water extracts contained Pb. CONCLUSIONS. Medicinal plants could pose chronic metal toxicity effects from continual bioaccumulation along the food chain. Furthermore, extraction of active ingredients with water was deemed to be safer than the use of alcohol extracts. Continuous monitoring of these medicinal plant materials is needed.