2 research outputs found
Modeling Nanosilver Transformations in Freshwater Sediments
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
Stream Dynamics and Chemical Transformations Control the Environmental Fate of Silver and Zinc Oxide Nanoparticles in a Watershed-Scale Model
Mathematical models are needed to
estimate environmental concentrations
of engineered nanoparticles (NPs), which enter the environment upon
the use and disposal of consumer goods and other products. We present
a spatially resolved environmental fate model for the James River
Basin, Virginia, that explores the influence of daily variation in
streamflow, sediment transport, and stream loads from point and nonpoint
sources on water column and sediment concentrations of zinc oxide
(ZnO) and silver (Ag) NPs and their reaction byproducts over 20 simulation
years. Spatial and temporal variability in sediment transport rates
led to high NP transport such that less than 6% of NP-derived metals
were retained in the river and sediments. Chemical transformations
entirely eliminated ZnO NPs and doubled Zn mobility in the stream
relative to Ag. Agricultural runoff accounted for 23% of total metal
stream loads from NPs. Average NP-derived metal concentrations in
the sediment varied spatially up to 9 orders of magnitude, highlighting
the need for high-resolution models. Overall, our results suggest
that “first generation” NP risk models have probably
misrepresented NP fate in freshwater rivers due to low model resolutions
and the simplification of NP chemistry and sediment transport