Abstract
The use of medicinal plants for the treatment of diseases including cancer in Africa is gaining recognition and wide acceptability. However, some of these plants may bio-accumulate trace metals including heavy metals in their tissues, resulting in potential safety hazards. A greenhouse study was set up to investigate the presence and levels of trace metals in five anticancer medicinal plants (Withania somnifera, Artemisia afra, Catharanthus roseus, Centella asiatica and Taraxacum officinale) harvested from soil treated with sewage sludge, poultry droppings, cow dung, biosolid and NPK as soil nutrient boosters. ICP-MS was used to determine the trace metal contents in the different parts of the plants upon harvest. The root of Centella asiatica harvested from soil treated with cow dung recorded the highest concentration of Mn (2739 ± 26.91 mg/kg) while the least Mn concentration (47.64 ± 0.63 mg/kg) was recorded in the stem of W. somnifera harvested from soil treated with cow dung. The leaves of A. afra harvested from sewage sludge treatment recorded the lowest concentration of U (0.06 ± 0.03 mg/kg). The values of other trace metals in the different plant parts ranged from 2.01-66.00 mg/kg for Pb, 11.16-499.51 mg/kg for Cu, 7.64-538.36 mg/kg for Cr, 60.15-953.11 mg/kg for Zn, 0.82-123.76 mg/kg for Co, and 17.79-499.51 mg/kg for Ni. The overall concentration of trace metals in the five plants across all the treatments and the control was above the permissible limit set by the World Health Organization (WHO) for safe human consumption. The bioaccumulation factor (BAF) for Zn, Cr and Pb was above 1 in the five plants across all the treatments and the control which showed that the plants are hyper-accumulators for Zn, Cr and Pb.