Abstract
AbstractThe sulfidation and aging of silver nanoparticles (Ag‐NPs) with natural organic matter (NOM) are major transformation processes along their pathway in wastewater treatment plants and surface waters. Although soils appear to be a sink for disposed Ag‐NPs, the impact of variable saturation on the transport and retention behavior in porous media is still not fully understood. We studied the behavior of sulfidized silver nanoparticles (S‐Ag‐NPs, 1 mg L−1) in saturated and unsaturated sand columns regarding the effects of (i) the presence of NOM (5 mg L−1) in the aquatic phase on retention, transport, and remobilization of S‐Ag‐NPs and (ii) the distribution and quantity of air‐water and solid‐water interfaces for different flow velocities determined via X‐ray microtomography (X‐ray μCT). Unsaturated transport experiments were conducted under controlled conditions with unit gradients in water potential and constant water content along the flow direction for each applied flux. It was shown that (i) NOM in S‐Ag‐NP dispersion highly increased the NP‐mobility; (ii) differences between saturated and unsaturated transport were increasing with decreasing flux and, consequently, decreasing water contents; (iii) both, solid‐water and air‐water interfaces were involved in retention of S‐Ag‐NPs aged by NOM. Using numerical model simulations and X‐ray μCT of flow experiments, the breakthrough of Ag‐NP could be explained by a disproportional increase in air‐water interfaces and an increasing attachment efficiency with decreasing water content and flow velocity.
Highlights
Silver nanoparticles (Ag‐NPs) are among the most commonly used engineered NPs
We studied the behavior of sulfidized silver nanoparticles (S‐aging of silver nanoparticles (Ag‐NPs), 1 mg L−1) in saturated and unsaturated sand columns regarding the effects of (i) the presence of natural organic matter (NOM) (5 mg L−1) in the aquatic phase on retention, transport, and remobilization of S‐Ag‐NPs and (ii) the distribution and quantity of air‐water and solid‐water interfaces for different flow velocities determined via X‐ray microtomography (X‐ray μCT)
It was shown that (i) NOM in S‐Ag‐NP dispersion highly increased the NP‐mobility; (ii) differences between saturated and unsaturated transport were increasing with decreasing flux and, decreasing water contents; (iii) both, solid‐water and air‐water interfaces were involved in retention of S‐Ag‐NPs aged by NOM
Summary
Silver nanoparticles (Ag‐NPs) are among the most commonly used engineered NPs. Their wide application in detergents, clothing, cosmetics, and medical care products leads to a wide environmental spreading (Gottschalk et al, 2013). Concentrations of Ag in environmental compartments have been determined to be in the range of ng L−1 for water and mg kg−1 for soil and sediments (Blaser et al, 2008; Gottschalk et al, 2009; McGillicuddy et al, 2017). Along their pathway in sewer systems, wastewater treatment plants, and surface waters Ag‐NP are sulfidized (S‐Ag‐NP) and coated by natural organic matter (NOM) (Brunetti et al, 2015; Dale et al, 2013; Kim et al, 2010; Lowry et al, 2012; Thalmann et al, 2016). The transformation of Ag‐NPs in the environment can significantly change their stability, mobility, and toxicity (Baalousha et al, 2016; Grillo et al, 2015)
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