Environmental Engineering Reference
In-Depth Information
Table 5 Silver
concentrations (nmol/kg)
reported in National Research
Council Canada (NRC-
CNRC) reference material for
trace metals in nearshore
seawater (CASS-4) and
estuarine water (SLEW-3)
Ag (pmol/kg)
CASS-4
Reference
SLEW-3
Ndung'u et al. ( 2001 )
56.6 ± 8.3
Yang and Sturgeon ( 2002 )
50.2 ± 0.7
17.9 ± 0.8
Ndung'u et al. ( 2006 )
78.6 ± 18.2
27.5 ± 7.1
Ranville and Flegal ( 2005 )
101 ± 2.6
36.3 ± 0.3
Morford et al. ( 2008 )
53 ± 3; 54 ± 6; 59 ± 10
Ndung'u ( 2011 )
22.5 ± 1.5
( 1970 ) used ratios of radiosilver ( 110m Ag/ 108m Ag) associated with the 1961-1962
atmospheric nuclear weapons testing period to date marine organisms; then, two of
these authors (Hodge and Folsom 1972 ) used those ratios and 90 Sr/ 110m Ag ratios in
particulate aerosols to independently estimate the global budget of atmospheric
“fallout” 110m Ag from that testing period. Murozumi et al. ( 1981 ) measured silver
concentrations, but not stable silver isotopic compositions in seawater by using iso-
tope dilution TIMS. Recent advances, however, have demonstrated that silver isoto-
pic ratios may be accurately and precisely measured in environmental materials
(Schönbächler et al. 2007 ; Luo et al. 2010 ). Therefore, we expect that silver isotopic
measurements will soon be employed to trace natural and industrial fl uxes of silver
and its biogeochemical cycling within the oceans.
4
Summary
Despite its relatively high acute toxicity to marine phytoplankton and invertebrates
and its increasing use as a biocide, silver measurements in seawaters are still few
and far apart. That paucity of data limits our understanding of its global biogeo-
chemical cycle and an assessment of its potential applicability as a tracer of anthro-
pogenic contamination of the oceans. The need for such an assessment has been
heightened by the dramatic increase in AgNPs over the past decade.
Available measurements indicate that silver has a nutrient-type behavior in the
oceans, and preliminary data indicate that its cycling is being perturbed by aeolian
inputs of industrial silver. However the processes governing silver's biogeochemical
cycle in the ocean are still subject to debate. For instance, precipitation/scavenging of
AgS species in oxygen-depleted waters has been proposed to play a role in silver
removal from ocean waters and subsequent accumulation in sediments. This hypoth-
esis could be tested by undertaking additional measurements in waters and sediments
in regions impacted by extensive oxygen minimum zones (OMZ). Furthermore,
analysis of silver concentrations in waters impacted by hydrothermal plumes could
resolve what their potential impact is on silver distribution in deep water masses.
In addition to the relative scarcity of reported silver concentration measurements
in the oceans, comparing those few measurements that do exist is hampered by
 
Search WWH ::




Custom Search