Fate of nanoparticles during alum and ferric coagulation monitored using single particle ICP-MS

Characterization of Nanoparticles in Ethanolic Suspension Using Single Particle Inductively Coupled Plasma Mass Spectrometry: Application for Cementitious Systems

Single particle inductively coupled plasma mass spectrometry (spICP-MS) is a well-established technique to characterize the size, particle number concentration (PNC), and elemental composition of engineered nanoparticles (NPs) and colloids in aqueous suspensions. However, a method capable of directly analyzing water-sensitive or highly reactive NPs in alcoholic suspension has not been reported yet. Here, we present a novel spICP-MS method for characterizing the main cement hydration product, i.e., calcium-silicate-hydrate (C-S-H) NPs, in ethanolic suspensions, responsible for cement strength. The method viability was tested on a wide range of NP compositions and sizes (i.e., from Au, SiO2, and Fe3O4 NP certified reference materials (CRMs) to synthetic C-S-H phases with known Ca/Si ratios and industrial cement hardening accelerators, X-Seed 100/500). Method validation includes comparisons to nanoparticle tracking analysis (NTA) and transmission/scanning electron microscopy (TEM/SEM). Results show that size distributions from spICP-MS were in good agreement with TEM and NTA for CRMs ≥ 51 nm and the synthetic C-S-H phases. The X-Seed samples showed significant differences in NP sizes depending on the elemental composition, i.e. CaO and SiO2 NPs were bigger than Al2O3 NPs. PNC via spICP-MS was successfully validated with an accuracy of 1 order of magnitude for CRMs and C-S-H phases. The spICP-MS Ca/Si ratios matched known ratios from synthetic C-S-H phases (0.6, 0.8, and 1.0). Overall, our method is applicable for the direct and element-specific quantification of fast nucleation and/or mineral formation processes characterizing NPs (ca. 50-1000 nm) in alcoholic suspensions.

Living in a transient world: ICP-MS reinvented via time-resolved analysis for monitoring single events

After 40 years of development, inductively coupled plasma-mass spectrometry (ICP-MS) can hardly be considered as a novel technique anymore. ICP-MS has become the reference when it comes to multi-element bulk analysis at (ultra)trace levels, as well as to isotope ratio determination for metal(loid)s. However, over the last decade, this technique has managed to uncover an entirely new application field, providing information in a variety of contexts related to the individual analysis of single entities (e.g., nanoparticles, cells, or micro/nanoplastics), thus addressing new societal challenges. And this profound expansion of its application range becomes even more remarkable when considering that it has been made possible in an a priori simple way: by providing faster data acquisition and developing the corresponding theoretical substrate to relate the time-resolved signals thus obtained with the elemental composition of the target entities. This review presents the underlying concepts behind single event-ICP-MS, which are needed to fully understand its potential, highlighting key areas of application (e.g., single particle-ICP-MS or single cell-ICP-MS) as well as of future development (e.g., micro/nanoplastics).

Speciation, controlling steps and pathways of silver release from the sludge generated from coagulation of wastewater spiked with silver nanoparticles

Sludge generated in wastewater treatment facilities is an integral part for the introduction of silver nanoparticles (AgNPs) to the terrestrial environment, which would cause some adverse ecosystem responses. The understanding of silver release process from the sludge is important to evaluate their risks. In this study, the amount and speciation of the released silver were investigated by taking the sludge generated by wastewater coagulation with AgNPs added (denoted as sludge_C-AgNPs) an example, and kinetic analysis and density functional theory (DFT) calculations were first used to explore the controlling steps and pathways about the silver release. The results showed that sludge_C-AgNPs could release the dissolved silver and the colloidal silver. Beside Cl^-, Ca²⁺ in the leaching solution could enhance the silver release of sludge_C-AgNPs, especially for the colloidal silver. The released colloidal silver restricted in size from 40 nm to 100 nm with irregular shape. Although the oxidative dissolution of Ag⁰ was the origin of the silver release pathways from the sludge_C-AgNPs, the silver diffusion was the controlling step due to the spontaneous binding between silver and the hydrolysates of polyaluminium chloride in sludge_C-AgNPs. However, Ca²⁺ in the leaching solution could occupy the binding site of silver on sludge_C-AgNPs, which would increase the diffusion rate of silver over the oxidative rate of Ag⁰. With this condition, the controlling step of silver release from sludge_C-AgNPs turned to the oxidative dissolution of Ag⁰. Our findings are important to assess the fate of AgNPs in wastewater treatment as well as sludge applications.

Silver Nanoparticles and Ionic Silver Separation Using a Cation-Exchange Resin. Variables Affecting Their Separation and Improvements of AgNP Characterization by SP-ICPMS

Silver nanoparticles (AgNPs) are frequently found in everyday products and, as a consequence, their release into the environment cannot be avoided. Once in aquatic systems, AgNPs interact with natural constituents and undergo different transformation processes. Therefore, it is important to characterize and quantify AgNPs in environmental waters in order to understand their behavior, their transformation, and their associated toxicological risks. However, the coexistence of ionic silver (Ag⁺) with AgNPs in aquatic systems is one of the greatest challenges for the determination of nanosilver. Ion-exchange resins can be used to separate Ag⁺ from AgNPs, taking advantage of the different charges of the species. In this work, Dowex 50W-X8 was used to separate Ag⁺ and AgNPs in order to easily determine AgNP concentrations using inductively coupled plasma optical emission spectroscopy. The separation methodology was successfully applied to river water samples with different ratios of Ag⁺ and AgNPs. However, the methodology is not useful for wastewater samples. The described methodology also demonstrated an improvement in the determination of the particle size of AgNPs present in river waters by single particle inductively coupled plasma mass spectrometry when a significant amount of Ag⁺ is also present.

The aggregation kinetics of manganese oxides nanoparticles in Al(III) electrolyte solutions: Roles of distinct Al(III) species and natural organic matters

This study explored the aggregation kinetics of manganese oxides (MnO_x) nanoparticles in Al(III) electrolyte solutions. This is a common process in both water treatments and the natural environment. The results show that aggregation kinetics are Al(III) species-dependent. Without natural organic matters (NOM), ferron Al_a (monomeric Al(III)) and ferron Al_b (polymeric Al(III)) are the main species controlling the Derjaguin-Landau-Verwey-Overbeek (DLVO) type aggregation behavior of MnO_x at pH 5.0 and 7.2, respectively. Al_a and Al_b can neutralize and reverse the negative charge of MnO_x. Correspondingly, the attachment efficiency as a function of Al(III) concentrations contains three stages: destabilization, diffusion-limited, and re-stabilization stage. Interestingly, due to the tiny size of Al_b nanoclusters, they behave similar to free ions and do not induce heteroaggregation at pH 7.2. The influence of some model NOM (i.e., bovine serum albumin (BSA), Sigma humic acid (HA), and alginate) was also studied. At pH 5.0, alginate polymers, while Sigma HA and BSA cannot be, are linked by Al(III) to form alginate gel clusters which bridge MnO_x nanoparticles, and thus induce bridging flocculation. At pH 7.2, NOM induce the aggregation of Al_b nanoclusters to form NOM-Al(III) aggregates through charge neutralization effects. Consequently, highly enhanced aggregation rate, due to the heteroaggregation between these aggregates and MnO_x, was observed.

Physico-chemical processes

The review scans research articles published in 2018 on physico-chemical processes for water and wastewater treatment. The paper includes eight sections, that is, membrane technology, granular filtration, flotation, adsorption, coagulation/flocculation, capacitive deionization, ion exchange, and oxidation. The membrane technology section further divides into six parts, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis/forward osmosis, and membrane distillation. PRACTITIONER POINTS: Totally 266 articles on water and wastewater treatment have been scanned; The review is sectioned into 8 major parts;  Membrane technology has drawn the widest attention from the research community.

Effects of environmentally relevant concentrations of mixtures of TiO2, ZnO and Ag ENPs on a river bacterial community

Effluent from wastewater treatment plants contains a wide variety of engineered nanoparticles (ENPs) released from different sources. Although single type ENPs have been studied extensively with respect to their environmental impact, ENPs in mixed forms have not been investigated much at environmentally relevant concentrations. This study was designed to test the effect of mixed ENPs at three combinations and concentrations on an aquatic bacterial community. After mixing artificial treated wastewater with river water and exposing the microbial community to ENPs for three days, the ENPs were characterized by SP-ICP-MS. Results from this study showed that: 1) the size distribution of Ti and Zn at the beginning and end of the experiment did not vary much among all tested conditions. For Ag, the most frequent size increased more than 2-fold when the highest Ag ENPs were added; 2) particle concentrations of ENPs generally correlated positively with added concentrations; 3) dissolved Zn and Ag increased significantly as a result of spike; and 4) the bacterial community structure was shifted significantly as a consequence of ENPs' addition. With the dominant population being suppressed, the community exposed to ENPs became more diverse and even. Surprisingly, further increase of the doses of the three ENPs did not bring significant change to the microbial community. These results revealed that ENPs could bring significant impacts to prokaryotes even at low concentrations. But these impacts do not necessarily correlate positively with doses.

Optimized coagulation pathway of Al13: Effect of in-situ Aggregation of Al13

The coagulation mechanism for removing particles by Al₁₃ has been extensively investigated for water treatments. It was widely accepted that Al₁₃ played important roles in coagulation mainly by charge neutralization and electrostatic patch. However, the discovery of Al₁₃ aggregates (Al₁₃agg) in flocs indicated that the real coagulation process should be different from the previous understanding, including when Al₁₃agg were generated and how it interacted with negative particles. The aggregation process of Al₁₃ during coagulation and its micro-interfacial effect on particle coagulation remains to be explored. In this study, to investigate the aggregation of Al₁₃ and its effect on coagulation performance, two parallel coagulation jar tests were conducted on silica suspensions by preformed Al₁₃agg and Al₁₃, respectively. The results showed that optimized coagulation for particle removal by Al₁₃ occurred from pH 7 to pH 9, which was dominated by the in-situ aggregation of Al₁₃. The results confirmed that Al₁₃agg were both present in flocs generated in two tests, however, the morphology and distribution of surface Al of flocs were different for two tests. The in-situ formed Al₁₃agg covered all over the silica particles in flocs, resulting in compact structure with rough surfaces, while the preformed Al₁₃agg mainly distributed on joint sites between particles, generating denser flocs with smooth surfaces. This difference verified that the in-situ aggregation of Al₁₃ was the key factor to optimized particle coagulation. The overall optimized particle coagulation by Al₁₃ should undergo the following pathway: charge neutralization - in-situ aggregation of Al₁₃ - inter-particle bridging.

Polypropylene-MWCNT composite degradation, release, detection, and toxicity of MWCNT during accelerated aging

Nanomaterials (NM) are incorporated into polymers to enhance their properties. However, there are a limited number of studies on the aging of these nanocomposites and the resulting potential release of NM. To characterize NM at critical points in their life cycles, polypropylene (PP) and multiwall carbon nanotube filled PP (PP-MWCNT) plates with different thicknesses (from 0.25 mm to 2 mm) underwent accelerated weathering in a chamber that simulates solar irradiation and rainfall. The physicochemical changes of the plates depended on the radiation exposure, the plate thickness, and the presence of CNT fillers. Photodegradation increased with aging time, making the exposed surface more hydrophilic, decreasing the surface hardness and creating surface stress-cracks. Aged surface and cross-section showed crazing due to the polymer bond scission and the formation of carbonyls. The degradation was higher near the UV-exposed surface as the intensity of the radiation and oxygen diffusion decreased with increasing depth of the plates, resulting in an oxidation layer directly proportional to oxygen diffusion. Thus, sample thickness determines the kinetics of the degradation reaction and the transport of reactive species. Plastic fragments, which are less than 1 mm, and free CNTs were released from weathered MWCNT-PP. The concentrations of released NM that were estimated using ICP-MS, increased with prolonged aging time. Various toxicity tests, including reactive oxygen species generation and cell activity/viability, were performed on the released CNTs. The toxicity of the released fragments and CNTs to A594 adenocarcinomic human alveolar basal epithelial cells was observed. The released polymer fragments and CNTs did not show significant toxicity under the experimental conditions in this study. This study will help manufacturers, users of consumer products with nanocomposites and policymakers in the development of testing guidelines, predictive models, and risk assessments and risk based-formulations of NM exposure.

Low risk posed by engineered and incidental nanoparticles in drinking water

Natural nanoparticles (NNPs) in rivers, lakes, oceans and ground water predate humans, but engineered nanoparticles (ENPs) are emerging as potential pollutants due to increasing regulatory and public perception concerns. This Review contrasts the sources, composition and potential occurrence of NNPs (for example, two-dimensional clays, multifunctional viruses and metal oxides) and ENPs in surface water, after centralized drinking water treatment, and in tap water. While analytical detection challenges exist, ENPs are currently orders of magnitude less common than NNPs in waters that flow into drinking water treatment plants. Because such plants are designed to remove small-sized NNPs, they are also very good at removing ENPs. Consequently, ENP concentrations in tap water are extremely low and pose low risk during ingestion. However, after leaving drinking water treatment plants, corrosion by-products released from distribution pipes or in-home premise plumbing can release incidental nanoparticles into tap water. The occurrence and toxicity of incidental nanoparticles, rather than ENPs, should therefore be the focus of future research.