Concentration of pollutants in the sediment deposits of dam reservoirs are highly influenced by the sediments different physical and geochemical parameters such as grain size, mineral structure, organic matter content and cation exchange capacity (Sedláček, 2013).

The fine particles such as clay has the ability of binding organic matter and metals due to several reasons.

The clays has a high specific surface area(SSA) which is the the total surface area per unit of mass. The SSA is dependent on the particle size, because it increases as the particles become smaller. Further clay has high cation exchange capacity(CEC) which is the capacity of hold and release cations like Cu2+  and Zn2+.

These cations are held by electrostatic forces due to the negatively charged clay layers.                                       

Clays tends to have a net negative charge as a result of ion substitution like the substitution of silica (Si4+) by aluminum (Al3+) in the mineral structure (Cornell University, 2007).

The substitution is possible due to the spacing between the sheets in the structure of clays.

The clays layered and relatively open structure, high SSA and net negative charge allows absorption of pollutants.

The clay capacity to bind organic matter also important. Heavy metals bind easily to organic matter therefore organic matter also has a net negative charge with an even higher CEC than clay. The organic matter CEC is pH dependent with higher CEC at higher pH values(Cornell University, 2007).

Because of these physical and chemical properties dissolved clay in streams can serve as a vehicle of transporting and spreading contaminants from one area to another.