Sources, Fluxes, and Biogeochemical Cycling of Silver in the Oceans - Reviews of Environmental Contamination and Toxicology - page 27

That scarcity of data on silver concentrations in the oceans raises the question:
Who cares? Silver was not included in the original list of elements for GEOTRACES,
“an international programme which aims to improve the understanding of biogeo-
chemical cycles and large-scale distribution of trace elements and their isotopes in
the marine environment” (GEOTRACES 2006 ), because it is neither a nutrient nor
a commonly used tracer in sea water. However, silver is extremely toxic to marine
phytoplankton and invertebrates, and its increasing use as a biocide has raised con-
cerns about its potential as an environmental pollutant (Purcell and Peters 1998 ).
Silver has been extracted from geological deposits since 300 BC (Nriagu 1996 ).
It has been mined directly, as well as extracted as a bi-product of gold, copper, lead
and zinc deposits. Ancient Greeks and Romans extracted considerable amounts of
silver for the production of silver bullion, and it has been used widely throughout
history for the production of currencies, ornaments and utensils. Technological inno-
vations since the 1800s have led to new uses of silver. In particular, its photochemical
properties were the basis for the development of photography.
However, environmental releases of industrial silver from industrial and municipal
wastewater outfalls, and from mining, smelting, and manufacturing operations have
adversely impacted the environment (Purcell and Peters 1998 ), primarily because
of silver's toxicity to invertebrates (Luoma et al. 1995 ). For example, wastewater
discharges of silver from a photography plant into San Francisco Bay measurably
decreased the fecundity of benthic invertebrates in the effl uent plume (Flegal et al.
2007 ). Although such discharges have substantially decreased in the United States
since the 1970s, industrial silver emissions are likely to have increased in rapidly
developing countries that possess limited silver recovery and treatment facilities
(Ranville and Flegal 2005 ).
Moreover, concerns with silver toxicity in aquatic environments have markedly
increased with the rapidly growing use of silver nanoparticles (AgNPs) as antimicro-
bial agents in a wide variety of consumer products (Blaser et al. 2008 ; Luoma 2008 ;
Bradford et al. 2009 ; Fabrega et al. 2011 ). As a result, there have recently been a
series of studies on AgNP's stability (e.g., Benn and Westerhoff 2008 ; Liu and Hurt
2010 ; Liu et al. 2010 ; Levard et al. 2012 ; Unrine et al. 2012 ; He et al. 2013 ; Chambers
et al. 2014 ), bioavailability to aquatic organisms (e.g., Li et al. 2013 ; Wang and Wang
2014 ), and toxicity to those organisms (e.g., Navarro et al. 2008 ; Bone et al. 2012 ;
Turner et al. 2012 ; He et al. 2013 ; Chambers et al. 2014 ). These studies build on
previous reports that addressed the bioaccumulation of silver in marine food chains
(e.g., Ettajani et al. 1992 ; Fisher et al. 1995 ; Fisher and Wang 1998 ; Xu and Wang
2004 ; Yoo et al. 2004 ; Long and Wang 2005 ; Ng and Wang 2007 ). Those and other
reports are summarized in Eisler's ( 2010 ) recent compendium on silver concentra-
tions in marine organisms. Ratte ( 1999 ) and Bianchini et al. ( 2005 ) also provided
earlier reviews on the bioaccumulation and toxicity of silver in marine organisms,
and there have been several complementary reports since then (e.g., Bianchini et al.
2005 ; Pedroso et al. 2007 ).
Silver, in its ionic form, is extremely toxic to some aquatic organisms, second to
only mercury (Luoma et al. 1995 ). As such it is listed by the U.S. Environmental
Protection Agency (USEPA) as a priority pollutant in natural waters. But, in marine