Heavy metal elements are found within our environment like in the water reservoirs, in excess of soil and atmosphere, due to numerous anthropogenic activities. The natural sources of heavy metal contamination are mainly through the interactions of various types of rocks (i.e., igneous, sedimentary and metamorphic) with the surrounding environment. (Siegel, 2002) In rock-forming minerals, the heavy metals are usually found. For example, nickel, cobalt, manganese, zinc, copper, and vanadium have most easily leached due to mineral weathering. In addition to the metals such as scandium, yttrium and other rare earth metal elements have intermediate stability and uranium or hafnium have weathering resistivity. When hot hydrothermal fluids pervade the rocks, all these metals are then concentrated and induces various chemical reactions which causes precipitation of minerals and formation of ores. (Bradl, 2005) Within sedimentary rocks, such kind of deposits are usually found because of their porous structures and high permeability.
An alternate to store heavy metals in soil include its storage as relocated rock fragments, insoluble minerals and organic matter (i.e., the solid phase), as water and air trapped within the soil (i.e., the liquid phase). These two phases (i.e., solid phase and liquid phase) interact with each other with different ions passing through the system. (Alloway, 1995) Different types of rock that the soil originated from, defies the concentration and uniqueness of the heavy metals. Most of the heavy metals are originated in the third layer of the soil. Elements of this layer are dissolved within the upper layer and then these dissolved elements move downwards or sideways to the lower layer, where these elements are deposited. (Drever, 1997) The cationic elements of the heavy metals may get attracted by the third layer due to the high concentration of iron oxyhydroxides and clay. (Bradl, 2005)