Medium (Pl. Media)
Medium (Pl. Media) : (a) Any one of the basic categories of material surrounding or contacting an organism (e.g., outdoor air. indoor air, water, soil, sediments) through which chemicals or pollutants can move and reach the organism. [USEPA, 1992a: Dermal Exposure Assessment]; (b) The environmental substance (e.g, air, water, soil) originally contaminated. [USEPA, 1999: Superfund Risk Assessment Glossary]