CHALCOGENS are elements belonging to periodic table group 16 and includes the elements oxygen, sulfur, selenium and tellurium, radioactive polonium and synthetic ununhexium.
Among these six elements, oxygen and sulfur are non-metals, while selenium, tellerium and polonium are metalloid semi-conductors. These elements, their bio-geological cycles and interactions with metals, still have many un-revealed scientific curiosities and technological potentials. Despite their appealing fundamental and practical importance, biogenic group 16 compounds have so far been less intensively investigated. However, over the past two decades, the finer aspects of the biogeochemical cycles of these chalcogens, particularly selenium, have begun to emerge. The chalcogen cycle also forms the basis of several environmental technologies to treat pollution. These include the biodegradation of organics driven by chalcogen bioconversion, nutrient removal processes based on chalcogen redox processes and the formation of thermodynamically stable chalcogen stocks.