Association colloids suspended in solution . Colloids are of interest to the environmental chemist for several reasons. Both organic and inorganic substances are transported as colloids. Although most pesticides and herbicides are not water soluble, they do aggregate with humic and fulvic acids, natural breakdown products of cellulose. Humic and fulvic acids form hydrophilic colloids in water, transporting pesticides and herbicides in the process.
Clays are the most common hydrophobic colloids in natural waters.
Clay is a generic term used to describe a class of secondary minerals produced from the weathering of aluminum silicate rocks. The composition and structure of clays give them the properties that result in colloidal behavior in water. Clays are flat sheets of alternating layers of silicon oxides and aluminum oxides, held together by ionic attraction for cations sandwiched between the sheets. Figure 5, shown below, is an example of kaolinite clay, illustrating the alternating sheets of silicon oxides and aluminum oxides. An example of kaolinite clay.