Sources of silver in the environment

Abstract

Silver is a naturally occurring metal that is extensively utilized in the photographic and imaging industry, as well as in electronics and electrical applications and other lesser uses. It is known to be discharged to the environment from its industrial applications, and this leads to the possibility for exposure to aquatic and terrestrial organisms. Because of great differences in toxicity between silver compounds, the form in which silver enters the environment is important. While the ionic form of silver has been shown to be toxic to a variety of aquatic organisms, forms of silver other than ionic, or free, silver are significantly less toxic. Ionic silver is known to convert to the more innocuous forms as it reacts rapidly with natural chemical ligands in sewer systems, sewage treatment facilities, and the environment. This paper reviews information on the industries that use silver, the quantities they employ, and the forms and amounts of silver that may be discharged from each into the environment.

Predicting toxicity of sediments spiked with silver

“…Silver is a highly toxic metal, with a wide distribution in the environment. Sediments are a dominant sink for silver released into aquatic environments [1]. Given that silver is one of the most strongly bioaccumulated of the elements [2], this combination of factors would seem to indicate that silver in sediments poses a large environmental risk.…”

“…However, little is known about the biological effects or bioavailability of sediment-associated silver in the field [2]. This is because silver is generally found in low concentrations as one component of a mixture of contaminants and because speciation is extremely important in silver toxicity [1].…”

Influence of water quality on silver toxicity to rainbow trout (Oncorhynchus mykiss), fathead minnows (Pimephales promelas), and water fleas (Daphnia magna)

“…[Ag] ϭ e 1.72[ln(hardness)]Ϫ6.52 which rearranges to ln[Ag] ϭ 1.72 ϫ ln(hardness) Ϫ 6.52 [1]. Current research has acknowledged this equation to be incomplete in estimating true acute silver toxicity [6,[9][10][11][12][13][14]. This equation does not include terms for water quality parameters such as alkalinity, dissolved organic carbon (DOC), or chloride, which have been shown to decrease mortality due to ionic silver exposure [6,7,9,10,[12][13][14].…”

Historical impacts of environmental regulation of silver

“…This would reduce regulatory requirements placed on silver and simplify its management, but would not remove environmental controls in surface water. Most silver finds its way into the environment not from solid waste, but from waterborne wastes; photoprocessing (including medical and dental X-ray and other photographic developing), electronics manufacture, metal plating operations, and other industrial operations contribute to the total amount of silver discharged to surface waters [37].…”