Determination Of Essential Trace Elements In Selected Medicinal Plants And Their Aqueous Extracts

ABSTRACT

It is becoming increasingly evident that trace elements such as chromium (Cr), manganese (Mn), zinc (Zn), vanadium (V) and iron (Fe) are therapeutically useful as they play vital role in immune boosting. It is therefore possible that effectiveness of certain medicinal plants may be due to either interaction of the metals with organic molecules or these trace elements alone are effective in improving or boosting immunity. There has been an increased use of medicinal plants due to high cost of drugs, drug resistance and increased awareness that medicinal plants contain valuable compounds. Great emphasis has been on organic compounds in these plants yet trace elements also play a vital role in the effectiveness of drugs. Hence there is need to determine the levels of these elements in medicinal plants and their aqueous extract. This work reports the determination of the levels of chromium, manganese, zinc, vanadium and iron in some selected medicinal plants and their aqueous extract used in Kenya. The medicinal plants were identified by a plant taxonomist. Sample of Markhamia platycalyx were collected randomly from Kakamega forest while Erythrina abyssinica, Prunus africana, Croton machrostachyus and Euphorbia candelabrum were collected from Nyeri. For each plant, samples were collected from three different regions separated by at least 10 km. A total of 105 samples were collected for each plant. Digestion was done using a mixture of acids and the level of these trace elements in digested sample and aqueous extract determined using atomic absorption spectrometry (AAS) and differential pulse anodic stripping voltammetry (DPASV). Dixon’s Q-test was used for the elimination of outlying data. Correlation analysis was done for levels of trace elements in plants and their aqueous extract. Erythrina abyssinica was found to be especially rich in trace elements with vanadium concentration being lowest (0.79 μg/g) while iron concentration being highest (452 μg/g). Markhamia platycalyx contained the lowest levels of trace elements ranging from 2.5 μg/g chromium to 87.4 μg/g iron. This could probably explain why Markhamia platycalyx with low levels of trace elements is used to treat the least number of diseases compared to other herbs analysed in this study. There was high level of iron (65 μg/g to 452 μg/g) in the five medicinal plants analysed while vanadium showed the lowest level (≤ 0.79 μg/g). Chromium was in the range of 1.9 μg/g to 5.6 μg/g, zinc 10.5 μg/g to 158.7 μg/g while manganese levels ranged from 13.2 μg/g to 219.2 μg/g. Vanadium was not detected in any of the aqueous extract. Chromium in the aqueous extract was in the range of 1.8 μg/g to 4.3 μg/g though not detected in Prunus africana and Croton macrostachyus. Manganese concentration in the aqueous extract ranged from 4.3 μg/g to 45.6 μg/g while that of iron 17.7μg/g to 224.5 μg/g. High levels of trace elements were detected in aqueous extract obtained from Erythrina abyssinica and Croton machrostachyus. The extract from these two plants are used to treat diseases which are as a result of deficiency or malnutrition. Extracts from Erythrina abyssimica, Croton macrostachyus and Euphorbia candelabnum can act as supplement for people with deficiency in these trace elements. The results obtained by atomic absorption spectrometry (AAS) and Differential pulse anodic stripping voltammetry (DPASV) showed no significance difference.