Heavy Metal Concentrations in Some Common Medicinal Plants from Different Geographical Locations in Douala, Cameroon

Abstract

This study was aimed at investigating and comparing the levels of five heavy metals; Pb, Cd, Cr, Zn, and Cu in both leaves, shoot and root samples of six common medicinal plants: Aloe vera, Ageratum conyzoides, Cleome ciliata, Cymbopogon citratus, Eremomastax speciosa, and Justicia secunda collected from refuse dumps, roadsides and residential areas in Douala. The plant samples collected were divided into different parts. Concentrations of heavy metals were determined using Atomic Absorption Spectrometry. Results revealed that the selected medicinal plants accumulate heavy metals at different concentrations. Heavy metals repartition decreased in the trend roots>shoots>leaves. There was a significant difference (p<0.0001) in the content of metals between plants from different collection points. Samples collected from refuse dumps showed significantly higher concentrations (p<0.0001) of heavy metals followed by roadsides, then residential areas. Comparison of results with defined permissible limits led to the conclusion that the levels of all five heavy metals were beyond the permissible limits in the majority of medicinal plants analyzed. Only Ageratum conyzoides was below the permissible limit for Cu. High heavy metal concentrations in plants indicate high level of contamination and this raises consumers' health risk concerns.