Contaminant release represents the point at which a pollutant escapes from its source into the open environment.  Release can occur from both natural and anthropogenic sources, and in the latter case either deliberately or accidentally.  Release can also occur into different environmental media (e.g. the atmosphere, surface or subsurface water, soil, biota), and via a range of different mechanisms.  How releases occur, and into which medium, depends to a large extent on the sources concerned, as the figure to the right indicates.