Long-Term Transformation and Fate of Manufactured Ag Nanoparticles in a Simulated Large Scale Freshwater Emergent Wetland

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 2 S (∼52%), whereas AgNPs in the subaquatic sediment were present as Ag 2 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).

Emerging Contaminant or an Old Toxin in Disguise? Silver Nanoparticle Impacts on Ecosystems

“…15,20 Soils were blended and provided by Soils and Sand (Durham, U.S.A.), and were a blend of three soils ("Sandhills", from Lemon Springs, NC, U.S.A.; "Clay" and "Topsoil", from Durham, NC, U.S.A.). The final soil had a texture of 63.9% sand, 28.3% silt, and 13.0% clay, with 5.1% loss on ignition.…”

Potential risks and benefits of nanotechnology: perceptions of risk in sunscreens

“…A recent study by demonstrated that 18 months after addition on Ag-NPs to freshwater mesocosms the speciation of Ag in sediments was indeed dominated by Ag 2 S and Ag complexed with reduced S in organic matter (Ag-sulfhydryl). However, Lowry et al (2012) also found that some of the added Ag added to the mesocosms was taken up by plants, fish and insects showing that Ag originating from the NPs was bioavailable, probably because of incomplete or slow sulphidation.…”

“…Although the use of silver in photography was found not to affect the performance of the biological wastewater treatment plants (Pavlostathis and Maeng 1998), the use of nanosilver may raise a new concern. Nanosilver may behave differently in the environment and may have a potential for adverse effects on environmental species (Choi and Hu 2009;Stensberg et al 2011;Sweet et al 2011;Lowry et al 2012).…”

“…Even under oxic conditions, freshwater may contain metal sulfide clusters that make sulfide available for reaction with silver (Rozan et al 2000). The sulphidation process will both alter the surface charge and dissolution rate of Ag-NPs , and also affect their reactivity, mobility and toxicity (Bianchini et al 2002;Levard et al 2012;Reinsch et al 2012). Silver sulfide and organic silver-sulfide compounds are very stable and represent an important type of environmentally relevant silver species.…”

Detection, characterization and quantification of inorganic engineered nanomaterials: A review of techniques and methodological approaches for the analysis of complex samples

“…SP-ICP-MS has also been applied to study the fate of silver nanoparticles in in vitro human digestion [104], lake mesocosms [50] and washing solutions from commercial detergents [90], to track their dissolution [127] and agglomeration [128] in natural waters or their release from food additives [129]. [142,143] and ZnO and CuO [144], and for speciation of silver in waters and soils from microcosm [145] and mesocosms [146] experiments.…”