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Quantification of engineered nanomaterials (ENMs) concentrations in surface waters remains one of the key challenges in environmental nanoscience and nanotechnology. A promising approach to estimate metal and metal oxide ENM concentrations in complex environmental samples is based on the increase in the elemental ratios of ENM-contaminated samples relative to the corresponding natural background elemental ratios. This contribution evaluated the detection and quantification of Ag, CeO 2 , and Fe 2 O 3 ENMs spiked in synthetic soft, or in natural river waters using the elemental ratio approach, and evaluated the effect of extractants including sodium hydroxide (NaOH), sodium oxalate (Na 2 C 2 O 4 ) and sodium pyrophosphate (Na 4 P 2 O 7 ) on the recovery of ENMs from the spiked waters. The extracted ENM concentrations were higher in Na 4 P 2 O 7 -extracted suspensions than in NaOH- and Na 2 C 2 O 4 -extracted suspensions due to the higher efficiency of Na 4 P 2 O 7 to break up natural and engineered nanomaterial heteroaggregates. The size distributions of the extracted suspensions were determined by asymmetrical flow-field flow fractionation coupled to inductively coupled plasma-mass spectrometer (AF4-ICP-MS). These size distribution analysis demonstrated that Ag ENMs were extracted from the spiked river water as both primary particles and small (<100 nm) aggregates, whereas CeO 2 ENMs were extracted from the spiked river water as aggregates of particles in the size range 0-200 nm. The number particle size distribution of the extracted suspensions confirmed that Ag ENMs were extracted as a mixture of primary and aggregated Ag ENMs. Small Ag ENMs (i.e. <20 nm) were detected by AF4-ICP-MS, but these particles were not detected by single particle (sp)-ICP-MS due to high size detection limit of sp-ICP-MS. This study illustrates that the elemental ratio approach is a promising approach to detect and quantify ENMs in surface waters. This study also illustrates the need for a multi-method approach, including extraction, filtration, AF4-ICP-MS and sp-ICP-MS, to detect, quantify, and characterize ENMs in surface waters., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Characterization and understanding of natural nanomaterials (NNMs) properties is essential to differentiate engineered nanomaterials (ENMs) from NNMs. However, NNMs in environmental samples typically occur as heteroaggregates with other particles, e.g., NNMs, ENMs, and larger particles. Therefore, there is a need to isolate NNMs into their primary particles to better characterize their physicochemical properties. Here, we evaluated the efficiency of sodium hydroxide, sodium oxalate, and sodium pyrophosphate to extract NNMs from surface waters. The extracted NNMs were characterized for total metal concentration by inductively coupled plasma-mass spectrometry (ICP-MS) following full digestion; size distribution, elemental composition and ratios by flow-field flow fractionation (AF4)-ICP-MS; and morphology by transmission electron microscopy (TEM). Sodium pyrophosphate extraction resulted in the highest NNM concentration and the smallest NNM size distribution. Sodium hydroxide and sodium oxalate extraction generated heteroaggregates with a broad size distribution. The NNM extraction efficiency increased with extractant (sodium oxalate and sodium pyrophosphate) concentration. The concentration of metals in the sodium pyrophosphate-extracted NNMs compared to the total metal concentration was element-dependent and varied from as high as >80% for Cu, Zn, and Sr to as low as <5% for Al, Ti, and Nb. This study provides a simple protocol for NNM extraction from complex environmental samples and provides a better understanding of NNM physicochemical properties. The presented NNM extraction protocol forms the basis for ENM extraction from natural waters., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Characterization of natural nanomaterial (NNM) physicochemical properties - such as size, size distribution, elemental composition and elemental ratios - is often hindered by lack of methods to disperse NNMs from environmental samples. This study evaluates the effect of extractant composition, pH, and ionic strength on soil NNM extraction in term of recovery and release of primary particles/small aggregate sizes (i.e., <200 nm). The extracted NNMs were characterized for hydrodynamic diameter and zeta potential by dynamic light scattering and laser Doppler electrophoresis, natural organic matter desorption by UV-Vis spectroscopy, element composition by inductively coupled plasma-mass spectroscopy (ICP-MS), size based elemental distribution by field flow fractionation coupled to ICP-MS, and morphology by transmission electron microscopy. The extracted NNM concentrations increased following the order of NaOH ≤ Na 2 CO 3  < Na 2 C 2 O 4  < Na 4 P 2 O 7 . Na 4 P 2 O 7 was the most efficient extractant and results in 2-12 folds higher NNM extraction than other extractants. The Na 4 P 2 O 7 extracted NNMs exhibited narrower size distribution with smaller modal size relative to NaOH, Na 2 CO 3 , Na 2 C 2 O 4 extracted NNMs. Thus, Na 4 P 2 O 7 enhances the extraction of primary NNMs and/or smaller NNM aggregates (i.e., size <200 nm). Na 4 P 2 O 7 promote soil microaggregates breakup and release of NNMs by reducing free multivalent cation concentration in soil pore water by forming metal-phosphate complexes and by enhancing NNM surface charge via phosphate sorption on NNM surfaces. Additionally, the extracted NNM concentrations increased with the increase in extractant concentration and pH, except at 100 mM where the high ionic strength might have induced NNM aggregation. The improved NNM-extraction will improve the overall understanding of the physicochemical properties of NNMs in environmental systems. This study presents the key properties of NNMs that can be used as background information to differentiate engineered nanomaterials (ENMs) from NNMs in complex environmental media., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Agglomeration and disagglomeration processes are expected to play a key role on the fate of engineered nanoparticles in natural aquatic systems. These processes are investigated here in detail by studying first the stability of TiO2 nanoparticles in the presence of monovalent and divalent electrolytes at different pHs (below and above the point of zero charge of TiO2) and discussing the importance of specific divalent cation adsorption with the help of the DLVO theory as well as the importance of the nature of the counterions. Then the impact of one polysaccharide (alginate) on the stability of agglomerates formed under pH and water hardness representative of Lake Geneva environmental conditions is investigated. In these conditions the large TiO2 agglomerates (diameter>1μm) are positively charged due to Ca(2+) and Mg(2+) specific adsorption and alginate, which is negatively charged, adsorbs onto the agglomerate surface. Our results indicate that the presence of alginate at typical natural organic matter concentration (1-10 mg L(-1)) strongly modifies the TiO2 agglomerate (50 mg L(-1)) stability by inducing their partial and rapid disagglomeration. The importance of disagglomeration is found dependent on the alginate concentration with maximum of disagglomeration obtained for alginate concentration ≥8 mg L(-1) and leading to 400 nm fragments. From an environmental point of view partial restabilization of TiO2 agglomerates in the presence of alginate constitutes an important outcome. Disagglomeration will enhance their transport and residence time in aquatic systems which is an important step in the current knowledge on risk assessment associated to engineered nanoparticles., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The physicochemical characteristics of hematite nanoparticles related to their size, surface area and reactivity make them useful for many applications, as well as suitable models to study aggregation kinetics. For several applications (such as remediation of contaminated groundwater) it is crucial to maintain the stability of hematite nanoparticle suspensions in order to assure their arrival to the target place. The use of biopolymers has been proposed as a suitable environmentally friendly option to avoid nanoparticle aggregation and assure their stability. The aim of the present work was to investigate the formation of complexes between hematite nanoparticles and a non-conventional galactomannan (vinal gum--VG) obtained from Prosopis ruscifolia in order to promote hematite nanoparticle coating with a green biopolymer. Zeta potential and size of hematite nanoparticles, VG dispersions and the stability of their mixtures were investigated, as well as the influence of the biopolymer concentration and preparation method. DLS and nanoparticle tracking analysis techniques were used for determining the size and the zeta-potential of the suspensions. VG showed a polydispersed size distribution (300-475 nm Z-average diameter, 0.65 Pdi) and a negative zeta potential (between -1 and -12 mV for pH2 and 12, respectively). The aggregation of hematite nanoparticles (3.3 mg/L) was induced by the addition of VG at lower concentrations than 2mg/L (pH5.5). On the other hand, hematite nanoparticles were stabilized at concentrations of VG higher than 2 mg/L. Several phenomena between hematite nanoparticles and VG were involved: steric effects, electrostatic interactions, charge neutralization, charge inversion and polymer bridging. The process of complexation between hematite nanoparticles and the biopolymer was strongly influenced by the preparation protocols. It was concluded that the aggregation, dispersion, and stability of hematite nanoparticles depended on biopolymer concentration and also on the way of preparation and initial physicochemical properties of the aqueous system., (Copyright © 2015 Elsevier B.V. All rights reserved.)