Definition: Sediment is an environmental substance comprised of any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bedor bottom of a body of water or other liquid.
Definition: Mucus is a bodily fluid consisting of a slippery secretion of the lining of the mucous membranes in the body. It is a viscous colloid containing antiseptic enzymes (such as lysozyme) and immunoglobulins. Mucus is produced by goblet cells in the mucous membranes that cover the surfaces of the membranes. It is made up of mucins and inorganic salts suspended in water.
Definition: Gravel is an environmental material which is composed of pieces of rock that are at least two millimeters (2mm) in its largest dimension and no more than 75 millimeters.