Silver [Ag, 47]
303
Silver accumulation by algae plays a crucial role in its cycling in aquatic
environments, and in its transfer to food chain. Zooplanktons contain Ag within the
order of 10–20 mg/kg ash weight (AW), and in phytoplanktons, it averages 4 mg/kg AW.
Mussels accumulate more Ag at low salinity than at high salinity. Mollusks contain
Ag within the range of <0.01–4.0 mg/kg fresh weight (FW) from the Baltic Sea and
0.002–0.09 mg/kg FW from the Atlantic coast of the United States (Szefer 2002).
Fish from rivers in the vicinities of towns may contain much higher amounts of Ag.
Apparently, it is the most easily available to trout (Ratie vide Kabata-Pendias and
Mukherjee 2007).
The median Ag concentration in bottled and tap waters of the EU countries
is fairly similar and is <1.0 ng/L (Birke et al. 2010). Drinking water in Finland
contains Ag at levels <30 ng/L (Kabata-Pendias and Mukherjee 2007). Its acceptable concentration is much higher, up to about 1000 ng/L. Its increased level,
up to about 50 μg/L, after using Ag filters for water cleaning, is not harmful to
humans. Due to inadequate data, health-based guideline value for Ag has not
been established.
However, there is a recommendation that Ag concentrations in drinking water
should not exceed 100 μg/L (WHO 2011a).
44.4 AIR
The world median Ag concentration in air is estimated to be 0.044 ng/m 3 (Reimann
and Caritat 1998). The background value of Ag contents of the atmosphere of Finland
is 0.014, 0.010, and 0.011 ng/m 3 , during summer, autumn, and winter, respectively
(Jalkanen and Häsänen vide Kabata-Pendias and Mukherjee 2007).
Silver in air occurs mainly in the forms of halides, sulfides, bromides, and oxides.
The wet Ag deposition in Sweden (in 1999) was 0.4 g/ha/yr, whereas in the United
Kingdom was up to 1 g/ha/yr (Eriksson 2001a).
44.5 PLANTS
Silver contents in plants vary greatly; the lowest are in cereals grains, <0.003 mg/kg,
and the highest in grass, <5  mg/kg, and in fungi, <150  mg/kg (Eriksson 2001a;
Falandysz et al. 2012). The common Ag concentrations in food plants range within
the order of 0.003–0.05 mg/kg.
The amounts of Ag in most plants are related to its contents of soils. Thus,
Ag can be concentrated to toxic levels in plants growing in Ag-contaminated or
Ag-mineralized areas. In plants, Ag is apparently deposited in root tissues, and
therefore is excluded from metabolic processes. However, when Ag is mobile
(e.g., AgNO 3 ), it may be taken up to toxic levels. Most sensitive to excess Ag levels
are lettuce, radish, and corn. Elevated Ag amounts reduce plant yields, often without
toxic symptoms. Interactions of Ag with some cations (e.g., K, Co, Cu) may result in
the inhibition of their uptake by plants.
Silver is very toxic to various bacteria, and thus, it is widely used as an ascetic
substance. It may precipitate some proteins in bacteria and form insoluble complexes
with ribonucleic acids.