Heavy metals are naturally occurrent in soils but may be
enhanced due to anthropogenic activities, such as mining, where
waste products can be highly concentrated in metallic elements. In
addition, processing and refinement of metals has caused wide-
spread environmental pollution with traces of various metals such
as lead (Pb), copper (Cu), cadmium (Cd) and zinc (Zn). High concentrations of heavy metals in soils
may cause long term risks to ecosystem associated with the transfer
of metals from the soil or sediment to the environment. For
example the risks associated with leaching (causing contamination of surface or groundwater) or absorption by living organisms such
as plants or humans are difficult to remove because heavy metals
persist in the environment.