Accumulation of Heavy Metals in Selected Medicinal Plants

Heavy metals (HMs) are natural components of the Earth's crust and are usually present in all environmental matrices. However, the concentration of several HMs has increased several fold in some ecosystems as a result of anthropogenic activities. Heavy environmental metal contamination has continued to gain global attention, mainly because of the toxicological risks posed by such metals to human health (Ayodeji and Olorunsola 2011). Although metallic elements are often essential for living organisms, they become toxic when present at high concentrations (Elekes et al. 2010). The rapid increase in human population, coupled with haphazard industrialization and technological advancement, has caused many serious environmental problems around the world; among the causes of such problems is the production and release of toxic metals. In the past few decades, the concentration of heavy metals in soil and surface waters has increased (Nriagu and Pacyna 1988; Larison et al. 2000) and now constitutes a potential threat to terrestrial and aquatic biota (Ives and Cardinale 2004; Nasim and Dhir 2010) and to humans by entering the food chain (Hsu et al. 2006; Meena et al. 2008). Because of the widespread presence of heavy metals in the environment, their residues also reach and are assimilated into medicinal plants. © 2011 Springer Science+Business Media, LLC.