Long-Term Transformation and Fate of Manufactured
Ag Nanoparticles in a Simulated Large Scale Freshwater Emergent Wetland
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Abstract
Transformations and long-term fate of engineered nanomaterials
must be measured in realistic complex natural systems to accurately
assess the risks that they may pose. Here, we determine the long-term
behavior of poly(vinylpyrrolidone)-coated silver nanoparticles (AgNPs)
in freshwater mesocosms simulating an emergent wetland environment.
AgNPs were either applied to the water column or to the terrestrial
soils. The distribution of silver among water, solids, and biota,
and Ag speciation in soils and sediment was determined 18 months after
dosing. Most (70 wt %) of the added Ag resided in the soils and sediments,
and largely remained in the compartment in which they were dosed.
However, some movement between soil and sediment was observed. Movement
of AgNPs from terrestrial soils to sediments was more facile than
from sediments to soils, suggesting that erosion and runoff is a potential
pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils
were transformed to Ag<sub>2</sub>S (∼52%), whereas AgNPs in
the subaquatic sediment were present as Ag<sub>2</sub>S (55%) and
Ag-sulfhydryl compounds (27%). Despite significant sulfidation of
the AgNPs, a fraction of the added Ag resided in the terrestrial plant
biomass (∼3 wt % for the terrestrially dosed mesocosm), and
relatively high body burdens of Ag (0.5–3.3 μg Ag/g wet
weight) were found in mosquito fish and chironomids in both mesocosms.
Thus, Ag from the NPs remained bioavailable even after partial sulfidation
and when water column total Ag concentrations are low (<0.002 mg/L)