Modeling
Nanosilver Transformations in Freshwater
Sediments
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Abstract
Silver
nanoparticles (AgNPs), an effective antibacterial agent,
are a significant and fast-growing application of nanotechnology in
consumer goods. The toxicity of AgNPs released to surface waters during
the use or disposal of AgNP-containing products will depend on the
chemical transformations the nanoparticles undergo in the environment.
We present a simple one-dimensional diagenetic model for predicting
AgNP distribution and silver speciation in freshwater sediments. The
model is calibrated to data collected from AgNP-dosed large-scale
freshwater wetland mesocosms. The model predicts that AgNP sulfidation
will retard nanoparticle oxidation and ion release. The resultant
Ag<sub>2</sub>S-coated AgNPs are expected to persist and accumulate
in sediment downstream from sources of AgNPs. Silver speciation and
persistence in the sediment depend on the seasonally variable availability
of organic carbon and dissolved oxygen. The half-life of typical sulfidized
(85% Ag<sub>2</sub>S) AgNPs may vary from less than 10 years to over
a century depending on redox conditions. No significant difference
in silver speciation and distribution is observed between ≥50%
Ag<sub>2</sub>S and 100% Ag<sub>2</sub>S AgNPs. Formation and efflux
of toxic silver ion is reduced in eutrophic systems and maximized
in oligotrophic systems