Heavy metal bioaccumulation in selected medicinal plants collected from Khetri copper mines and comparison with those collected from fertile soil in Haridwar, India

Heavy metal distribution in medicinal plants is gaining importance not only as an alternative medicine, but also for possible concern due to effects of metal toxicity. The present study has been focused on emphasizing the heavy metal status and bioaccumulation factors of V, Mn, Fe, Co, Cu, Zn, Se (essential metals) and Cr, Ni, Cd, As and Pb (potentially toxic metals) in medicinal plants grown under two different environmental conditions e.g., near to Khetri copper mine and those in fertile soils of Haridwar, both in India, using Instrumental Neutron Activation Analysis (relative method) and Atomic Absorption Spectrometry. The copper levels in the medicinal plants from Khetri were found to be 3-4 folds higher (31.6-76.5 mg kg-1) than those from Haridwar samples (7.40-15.3 mg kg-1), which is correlated with very high copper levels (763 mg kg-1) in Khetri soil. Among various heavy metals, Cr (2.60-5.92 mg kg-1), Cd (1.47-2.97 mg kg-1) and Pb (3.97-6.63 mg kg-1) are also higher in concentration in the medicinal plants from Khetri. The essential metals like Mn (36.4-69.3 mg kg-1), Fe (192-601 mg kg-1), Zn (24.9-49.9 mg kg-1) and Se (0.13-0.91 mg kg-1) and potentially toxic metals like Ni (3.09-9.01 mg kg-1) and As (0.41-2.09 mg kg-1) did not show much variations in concentration in the medicinal plants from both Khetri and Haridwar. The medicinal plants from Khetri, e.g., Ocimum sanctum, Cassia fistula, Withania somnifera and Azadirachta Indica were found rich in Ca and Mg contents while Aloe barbadensis showed moderately high Ca and Mg. Higher levels of Ca-Mg were found to correlate with Zn (except Azadirachta Indica). The bioaccumulation factors (BAFS) of the heavy metals were estimated to understand the soil-to-plant transfer pattern of the heavy metals. Significantly lower BAF values of Cu and Cr were found in the medicinal plants from Khetri, indicating majority fraction of these metals are precipitated and were immobilized species unsuitable for plant uptake. Overall, Withania somnifera (Ashwagandha) showed very high metal bioaccumulation.