Profile of Heavy Metals in Selected Medicinal Plants Used for the Treatment of Diabetes, Malaria and Pneumonia in Kisii Region, Southwest Kenya

Abstract

2 Abstract: Medicinal herbs are sources of chemical substances that have different biological activities including those useful in the treatment of human and animal diseases. Amongst the indigenous herbs used as phytomedicines for the treatment of diabetes, malaria and pneumonia in Kisii region, Southwest Kenya are Carissa spinarum, Urtica dioica, Warburgia ugandensis, Senna didymobotrya, Physalis Peruvian, Bidens pilosa, Leonotis nepetifolia and Toddalia asiatica. A study was carried out on these herbs in the year 2011 to 2012. The objective was to determine the essential and non-essential heavy metals present in the herbs and their levels. Leaf samples of these plants were obtained from Kisii region, washed, air-dried and milled. The samples were digested by wet digestion method and analysed by atomic absorption spectrometry. The essential and non-essential heavy metals in the plant extracts were quantified. As a guideline, FAO/WHO defined the permissible limits (ppm) of the various heavy metals in the consumed medicinal herbs for different countries as: chromium (2), manganese (44.6 to 339), iron (261 to 1239), cobalt (0.14 to 0.48), nickel (1.63), copper (20 to 150), zinc (27.4), cadmium (0.3), mercury (0.1) and lead (10). Results obtained in the present study showed that extracts of the medicinal herbs investigated contain heavy metals namely iron, chromium, copper, zinc, cobalt, manganese and nickel that are considered essential elements; and lead, cadmium and mercury which are non- essential. The concentration (ppm) of heavy metals in the plant extracts was found to be as follows: chromium (0.567 to 2.035), manganese (3.254 to 17.33), iron (0.967 to 6.067), cobalt (0.967 to 6.067), nickel (0.589 to 1.60), copper (0.305 to 1.44), zinc (0.989 to 1.833), cadmium (0.035 to 0.206), mercury (0.0024 to 0.00838) and lead (0.25 to 0.407). From the comparison of the results with the defined permissible limits, it was concluded that the levels of heavy metals present in the herbs fall in the permissible range for consumed medicinal herbs as defined for different countries.