_
_
_
_
302
Trace Elements in Abiotic and Biotic Environments
The common Ag species in soils are simple cations, Ag + , Ag 2+ , and AgO + .
_
Complex Ag anions predominate in soil solutions: AgCl , AgCl 3
2 , and Ag(SO ) 2
3
2
4
(Kabata-Pendias and Sadurski 2004). Despite several mobile species, Ag is slightly
mobile, especially in soils with pH > 4, and with higher organic matter (OM)
contents.
Silver in soil is primarily in the form of sulfide and chloride compounds, associated
with Fe, Pb, and Mn. Its behavior is controlled mainly by pH–Eh conditions and OM,
which may absorb relatively high Ag amounts. The maximum binding capacity of humic
acid and fulvic acid ranges from 0.8 to 1.9 mM/g, at pH 6.5. In general, the sorption of Ag
by soil components is very strong, and nearly half of the total Ag is in immobile species.
The contents of OM in soils may control the phytoavailability of Ag. Thus, the excess of
Ag in soils of low OM contents is more phytotoxic than in soils of high OM contents. The
elevated Ag contents of soils are toxic, especially to meso- and microbiota.
44.3 WATERS
Data for mean Ag concentrations in ocean waters are variable. According to Andren
and Bober (2002), these values vary from <0.024 to 0.56 ng/L, whereas Reimann
and de Caritat (1998) gave its concentration within the range of 2–40 ng/L, and in
stream waters, it may be elevated up to 190 ng/L. Other data on Ag in waters are as
follows (in ng/L): <0.01–140 in river waters and 0.2–0.5 in lake waters (Andren and
Bober 2002). After the program of clean technology (after 1980), concentrations of
Ag, especially in surface waters, have significantly decreased.
Silver in water occurs in several ionic species, associated mainly with Cl, S, and
+
NO 3 . The common species that control its mobility are Ag , AgCl , and AgCl . Also
2
3
several organic and inorganic complex compounds of Ag are present in water. Almost
all Ag species and compounds are readily scavenged by suspended minerals and
deposited in bottom sediments. The highest Ag contents, 25–>30 mg/kg, are reported
for sediments of river estuaries. Fine granulometric fractions of lake sediments contain
Ag up to 3.4 mg/kg, whereas in sandy sediments its amounts do not exit 0.1 mg/kg
(Bojakowska vide Kabata-Pendias and Mukherjee 2007). Bottom sediments are
principal sinks for Ag, which may cause an environmental risk. Depending on several
properties of sediments, such as salinity, pH, hydroxides of Fe and Mn, and OM, Ag
may become slightly mobile and remains deposited for over 100 years.
Silver is a highly reactive element in aquatic environments, and only the free
ionic species, Ag + , is highly toxic, even at low levels. Luckily, this Ag cation exists in
water for quite a short time, due to reactions with organic and inorganic ligands. The
toxicity of Ag in seawater is still not well understood. It depends on reactions of fish
gills, which under elevated Ag concentration failure the functions, and fish appear
to die. However, the toxicity of Ag concentrations is relatively high and estimated
for freshwater organisms between 0.85 and 1542 μg/L, and for seawater organisms,
13.3–2700 μg/L (Andren and Bober 2002). Several other water properties have also
significant impact on the Ag toxicity to aquatic biota. Silver occurs naturally, mainly
in the form of its very insoluble and immobile oxides, sulfides, and some salts. It has
occasionally been found in groundwater, surface water, and drinking water at concentrations about 5000 μg/L.
_
_
_
302
Trace Elements in Abiotic and Biotic Environments
The common Ag species in soils are simple cations, Ag + , Ag 2+ , and AgO + .
_
Complex Ag anions predominate in soil solutions: AgCl , AgCl 3
2 , and Ag(SO ) 2
3
2
4
(Kabata-Pendias and Sadurski 2004). Despite several mobile species, Ag is slightly
mobile, especially in soils with pH > 4, and with higher organic matter (OM)
contents.
Silver in soil is primarily in the form of sulfide and chloride compounds, associated
with Fe, Pb, and Mn. Its behavior is controlled mainly by pH–Eh conditions and OM,
which may absorb relatively high Ag amounts. The maximum binding capacity of humic
acid and fulvic acid ranges from 0.8 to 1.9 mM/g, at pH 6.5. In general, the sorption of Ag
by soil components is very strong, and nearly half of the total Ag is in immobile species.
The contents of OM in soils may control the phytoavailability of Ag. Thus, the excess of
Ag in soils of low OM contents is more phytotoxic than in soils of high OM contents. The
elevated Ag contents of soils are toxic, especially to meso- and microbiota.
44.3 WATERS
Data for mean Ag concentrations in ocean waters are variable. According to Andren
and Bober (2002), these values vary from <0.024 to 0.56 ng/L, whereas Reimann
and de Caritat (1998) gave its concentration within the range of 2–40 ng/L, and in
stream waters, it may be elevated up to 190 ng/L. Other data on Ag in waters are as
follows (in ng/L): <0.01–140 in river waters and 0.2–0.5 in lake waters (Andren and
Bober 2002). After the program of clean technology (after 1980), concentrations of
Ag, especially in surface waters, have significantly decreased.
Silver in water occurs in several ionic species, associated mainly with Cl, S, and
+
NO 3 . The common species that control its mobility are Ag , AgCl , and AgCl . Also
2
3
several organic and inorganic complex compounds of Ag are present in water. Almost
all Ag species and compounds are readily scavenged by suspended minerals and
deposited in bottom sediments. The highest Ag contents, 25–>30 mg/kg, are reported
for sediments of river estuaries. Fine granulometric fractions of lake sediments contain
Ag up to 3.4 mg/kg, whereas in sandy sediments its amounts do not exit 0.1 mg/kg
(Bojakowska vide Kabata-Pendias and Mukherjee 2007). Bottom sediments are
principal sinks for Ag, which may cause an environmental risk. Depending on several
properties of sediments, such as salinity, pH, hydroxides of Fe and Mn, and OM, Ag
may become slightly mobile and remains deposited for over 100 years.
Silver is a highly reactive element in aquatic environments, and only the free
ionic species, Ag + , is highly toxic, even at low levels. Luckily, this Ag cation exists in
water for quite a short time, due to reactions with organic and inorganic ligands. The
toxicity of Ag in seawater is still not well understood. It depends on reactions of fish
gills, which under elevated Ag concentration failure the functions, and fish appear
to die. However, the toxicity of Ag concentrations is relatively high and estimated
for freshwater organisms between 0.85 and 1542 μg/L, and for seawater organisms,
13.3–2700 μg/L (Andren and Bober 2002). Several other water properties have also
significant impact on the Ag toxicity to aquatic biota. Silver occurs naturally, mainly
in the form of its very insoluble and immobile oxides, sulfides, and some salts. It has
occasionally been found in groundwater, surface water, and drinking water at concentrations about 5000 μg/L.