Copper [Cu, 29]
Copper, a metal of the group 11 in the periodic table of elements, occurs in the Earth’s crust within the range of 25–75 mg/kg. It is concentrated mainly in mafic igneous rocks, up to 120 mg/kg, whereas in acidic igneous rocks its contents range from 5 to 30 mg/kg. The worldwide average copper content is estimated at 14 mg/kg. However, it highly varies for different countries, within the range between 14 and 110 mg/kg. In most cases, copper is accumulated in the upper few centimeter layer, mainly due to bioaccumulation and anthropogenic sources. The speciation of copper in water controls biochemical processes and its bioavailability. It occurs in forms of various cations, soluble salts such as carbonates and sulfates, and complexes with organic colloids. Concentration of copper in water is in dynamic equilibrium with its contents in surface-bottom sediments. Copper content in bottom sediments is a good indicator on its content in water.