Retention and remobilization mechanisms of environmentally aged silver nanoparticles in an artificial riverbank filtration system

Abstract

Riverbank filtration systems are important structures that ensure the cleaning of infiltrating surface water for drinking water production. In our study, we investigated the potential risk for a breakthrough of environmentally aged silver nanoparticles (Ag NP) through these systems. Additionally, we identified factors leading to the remobilization of Ag NP accumulated in surficial sediment layers in order to gain insights into remobilization mechanisms. We conducted column experiments with Ag NP in an outdoor pilot plant consisting of water-saturated sediment columns mimicking a riverbank filtration system. The NP had previously been aged in river water, soil extract, and ultrapure water, respectively. We investigated the depth-dependent breakthrough and retention of NP. In subsequent batch experiments, we studied the processes responsible for a remobilization of Ag NP retained in the upper 10 cm of the sediments, induced by ionic strength reduction, natural organic matter (NOM), and mechanical forces. We determined the amount of remobilized Ag by ICP-MS and differentiated between particulate and ionic Ag after remobilization using GFAAS. The presence of Ag-containing heteroaggregates was investigated by combining filtration with single-particle ICP-MS. Single and erratic Ag breakthrough events were mainly found in 30 cm depth and Ag NP were accumulated in the upper 20 cm of the columns. Soil-aged Ag NP showed the lowest retention of only 54%. Remobilization was induced by the reduction of ionic strength and the presence of NOM in combination with mechanical forces. The presence of calcium in the aging- as well as the remobilizing media reduced the remobilization potential. Silver NP were mainly remobilized as heteroaggregates with natural colloids, while dissolution played a minor role. Our study indicates that the breakthrough potential of Ag NP in riverbank filtration systems is generally low, but the aging in soil increases their mobility. Remobilization processes are associated to co-mobilization with natural colloids.

Analytical applications of single particle inductively coupled plasma mass spectrometry: a comprehensive and critical review

“…Whereas the release studies discussed above involve consumer and industrial products, fate studies are mostly based on the use of pristine and well-characterised nanoparticles, commercially available or synthesized at the laboratory, although aged nanoparticles have also been used. 164 The nanoparticles are spiked in the matrix of interest and the samples analysed directly or after undergoing the simulated process under study (e.g., gastrointestinal digestion, laundry, wastewater treatment, environmental exposure). The main advantage of these controlled experiments is that both size and concentration of the spiked nanoparticles can be selected as desired.…”

“…Soil studies have focused on the interaction of the nanoparticles with soil components, that control their transformations as well as their retention and mobility. 157,162,164,165 Most studies with environmental samples have focused on Ag nanoparticles, 104,[121][122][123][124][125][126][129][130][131][132][133][134][135][137][138][139][140][141][142][143][146][147][148]150,[152][153][154][155][156][157][158][159][160]275,163,164,166 as well as their transformation products, Ag 2 S and AgCl. 134,140 Other nanoparticles studied include TiO 2 , 136,144,148,...…”

“…Fate studies focus on the transformations of the nanoparticles in relation to their potential toxicity. [130][131][132]136,138,141,149,155,164 In general, the mean/median size and size distributions are the most frequent measurands. These measurands are related to the stability of the nanoparticles, but also to their aggregation 110,[122][123][124][125][126][127][128][129]131,133,136,138,139,141,145,148,152,157,158,[162][163][164]166 and dissolution.…”

“…[130][131][132]136,138,141,149,155,164 In general, the mean/median size and size distributions are the most frequent measurands. These measurands are related to the stability of the nanoparticles, but also to their aggregation 110,[122][123][124][125][126][127][128][129]131,133,136,138,139,141,145,148,152,157,158,[162][163][164]166 and dissolution. 138,143,144,147,151 For this reason, the concentration of the dissolved element has also been considered in different studies.…”

Transport and retention of engineered silver nanoparticles in carbonate-rich sediments in the presence and absence of soil organic matter

“…Transport studies for AgNPs have been carried out to improve our understanding of factors that control their environmental fate and to better assess potential risks. Many previous transport studies have been conducted in pure quartz sands (Liang et al, 2013b;Tian et al, 2010), topsoils (Braun et al, 2015;Cornelis et al, 2013;Liang et al, 2013a;Makselon et al, 2018;Makselon et al, 2017;Sagee et al, 2012), sand filters (Degenkolb et al, 2018), or consolidated rock such as sandstone (Neukum et al, 2014a,b). Calcium-based carbonate minerals such as calcite (CaCO 3 ) or dolomite (CaMg [CO 3 ] 2 ) are major components of carbonate aquifers around the world that are vital for drinking-water production (Bayat et al, 2014).…”