Sulfur hexafluoride (SF₆) is a nontoxic and extremely stable gas that is found in trace amounts in the atmosphere. SF₆ is primarily used as an electrical insulator in high-voltage switches and industrial production has steadily increased since 1953 (Maiss and Brenninkmeijer, 1998).  Concentrations of SF₆ in the atmosphere have rapidly increased over the past 35 years and are expected to continue to increase in the future whereas concentrations of CFCs are expected to decline.  Current atmospheric concentrations of SF₆ are between 4 and 5 pptv (parts per trillion by volume).  Busenberg and Plummer (2000) describe a method for using SF₆ to date young ground waters that is based on the known atmospheric history and the high rate of increase in the atmosphere (7% per year).

Biodegradation, sorbtion onto organic matter, and highly reducing conditions apparently do not significantly affect SF₆ concentrations in ground water.  SF₆, unlike CFCs,  is not present in common household products and contamination is not expected in urban environments.  Possible limitations of the SF₆ dating method are the presence of natural SF₆ sources (minerals and igneous rocks) and addition of atmospheric concentrations as excess air during recharge (Busenberg and Plummer (1997).

Busenberg, Eurybiades, and Plummer, L.N., 1997, Use of sulfur hexafluoride as a dating tool and as a tracer of igneous and volcanic fluids in ground water. Geological Society of America, Salt Lake City, 1997, Abstracts and Programs, v. 29, no. 6, p. A-78.

Busenberg Eurybiades, and Plummer, L.N., 2000, Dating young ground water with sulfur hexafluoride: Natural and anthropogenic sources of sulfur hexafluoride: Water Resources Research, v. 36, no. 10, p. 3011-3030.

Maiss M., and Brenninkmeijer, C. A. M., 1998, Atmospheric SF₆: Trends, sources, and prospects:  Environ. Sci. Technol., v. 32, p. 3077-3086.

Plummer, L.N., and Busenberg, Eurybiades, 2000, Chlorofluorocarbons, in Cook, P.G., and Herczeg, Andrew, eds., Environmental tracers in subsurface hydrology: Kluwer Academic Publishers, p. 441-478.