Nanoplastic Labelling with Metal Probes: Analytical Strategies for Their Sensitive Detection and Quantification by ICP Mass Spectrometry

The detection and quantification of nanoplastics in aquatic environments is one of the major challenges in environmental and analytical research nowadays. The use of common analytical techniques for this purpose is not only hampered by the size of nanoplastics, but also because they are mainly made of carbon. In addition, the expected concentrations in environmental samples are below the detection limit of the majority of analytical techniques. In this context, the great detection capabilities of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) in its Single Particle mode (SP-ICP-MS) have made of this technique a good candidate for the analysis of nanoplastics. Since the monitoring of carbon by ICP-MS faces several difficulties, the use of metal tags, taking advantage of the great potential of nanoplastics to adsorb chemical compounds, has been proposed as an alternative. In this perspectives paper, three different strategies for the analysis of polystyrene (PS) nanoplastics by SP-ICP-MS based on the use of metals species (ions, hydrophobic organometallic compound, and nanoparticles) as tags are presented and discussed. Advantages and disadvantages of each strategy, which rely on the labelling process, are highlighted. The metal nanoparticles labelling strategy is shown as a promising tool for the detection and quantification of nanoplastics in aqueous matrices by SP-ICP-MS.

EvaluationofremovalefficiencyofFe(III)andAl(III)ionsinacidsulfate waterusing agarose-basedmagnesiumoxidecomposite

Agarose/MgO composite adsorbents were developed through interspersing MgO nanoparticles with agarose to create an absorbent. The elimination capacity of the composite towards iron (Fe), aluminium (Al), and arsenate (As) in acid sulfate water was evaluated by means of batch method at room temperature. The constituents of the composite were characterized by thermal gravimetric analysis (TGA). The removal efficiency was determined through inductively coupled plasma (ICP) mass spectrometry. The composite adsorbent exhibited an excellent adsorption capacity towards three types of ions and heavy metals that are found in acid sulfate water. After treating with agarose/MgO, the concentrations of Fe and Al decreased from 60.28 and 604.84 μg/l, respectively, to under 3.42 and 1.78 μg/l, respectively. These exceptional results reveal the potential uses of agarose/MgO composites as adsorbents in the treatment of acid sulfate water.

Sorption and Desorption of Vanadate, Arsenate and Chromate by Two Volcanic Soils of Equatorial Africa

Sorption of oxyanions by soils and mineral surfaces is of interest due to their role as nutrients or pollutants. Volcanic soils are variable charge soils, rich in active forms of aluminum and iron, and capable of sorbing anions. Sorption and desorption of vanadate, arsenate, and chromate by two African andosols was studied in laboratory experiments. Sorption isotherms were determined by equilibrating at 293 K soil samples with oxyanion solutions of concentrations between 0 and 100 mg L−1 V, As, or Cr, equivalent to 0−2.0 mmol V L−1, 0−1.3 mmol As L−1, and 0−1.9 mmol Cr L−1, in NaNO3; V, As, or Cr were determined by ICP-mass spectrometry in the equilibrium solution. After sorption, the soil samples were equilibrated with 0.02 M NaNO3 to study desorption. The isotherms were adjusted to mathematical models. After desorption with NaNO3, desorption experiments were carried out with a 1 mM phosphate. The sorption of vanadate and arsenate was greater than 90% of the amount added, while the chromate sorption was much lower (19–97%). The sorption by the Silandic Andosol is attributed to non-crystalline Fe and Al, while in the Vitric Andosol, crystalline iron species play a relevant role. The V and Cr sorption isotherms fitted to the Freundlich model, while the As sorption isotherms conformed to the Temkin model. For the highest concentrations of oxyanions in the equilibrating solution, the sorbed concentrations were 37–38 mmol V kg−1, 25 mmol As kg−1, and 7.2–8.8 mmol Cr kg−1. The desorption was low for V and As and high for Cr. The comparison of the sorption and desorption isotherms reveals a pronounced hysteresis for V in both andosols and for Cr in the Silandic Andosol. Phosphate induced almost no V desorption, moderate As desorption, and considerable Cr desorption.

Chemical and physical heterogeneity within native gold: implications for the design of gold particle studies

Studies of populations of gold particles are becoming increasingly common; however, interpretation of compositional data may not be straightforward. Natural gold is rarely homogenous. Alloy heterogeneity is present as microfabrics formed either during primary mineralization or by modification of pre-existing alloys by chemical and physical drivers during subsequent residence in either hypogene or surficial environments. In electron-probe-microanalysis (EPMA)-based studies, the combination of Cu, Hg, and Pd values and mineral inclusion suites may be diagnostic for source style of mineralization, but Ag alone is rarely sufficient. Gold characterization studies by laser-ablation-ICP mass spectrometry linked to both quadrupole and Time-of-Flight (ToF-MS) systems show that only Ag, Cu, and Hg form homogenous alloys with Au sufficiently often to act as generic discriminants. Where present, other elements are commonly distributed highly heterogeneously at the micron or submicron scale, either as mineral inclusions or in highly localized, but low concentrations. Drawing upon our own data derived from individual inspection and analyses of approximately 40,000 gold particles from 526 placer and in situ localities worldwide, we show that adequate characterization of gold from a specific locality normally requires study of a minimum of 150 particles via a two-stage approach comprising spatial characterization of compositional heterogeneity, plus crystallographic orientation mapping, that informs subsequent targeted acquisition of quantitative compositional data by EPMA and/or laser-ablation ICP-MS methods. Such data provide the platform to review current understanding of the genesis of gold particle characteristics, elevating future compositional studies from empirical descriptions to process-focused interpretations.