Polyvinylidene Fluoride Micropore Membranes as Solid-Phase Extraction Disk for Preconcentration of Nanoparticulate Silver in Environmental Waters

Species selective concentration and determination of nano-selenium and inorganic selenium species in environmental waters by micropore membrane filtration and ICP-MS

Accurate quantification of nano-selenium (nSe) and other ionic Se species in aquatic environments is a prerequisite for reliable estimation of their potential hazards. In this study, a micropore membrane filtration-based method followed by ICP-MS analysis was proposed for the selective concentration and determination of nSe in the water column. Polyvinylidene fluoride (PVDF) and nylon micropore filtration membranes were proven to efficiently capture nSe under optimal conditions (retention > 91.0 ± 0.87%). At the same time, ionic selenite and selenate could escape from the membranes, realizing the isolation of nSe and ionic Se species. The interference of dissolved organic matter (DOM) during separation can be resolved by adding Ca(II) ions, which can induce the formation of DOM aggregates by cation bridging effects. nSe retained on PVDF membranes could be effectively eluted with FL-70 (a powerful alkaline surfactant) aqueous solutions (0.5%, m/v) while maintaining the original size and morphology. Although nSe trapped on nylon membranes could not be easily eluted, quantification can also be achieved after membrane digestion. Speciation of ionic selenite and selenate in the filtrate was further conducted with an anion exchange column by using HPLC coupled with ICP-MS. The developed method was used to analyze Se species in six real water samples. Spiking experiments showed that the recoveries of nSe ranged from 70.2 ± 2.7% to 85.8 ± 1.3% at a spike level of 0.2 µg/L, and the recoveries of Se(IV) and Se(VI) ranged from 83.6 ± 0.5% to 101 ± 1% at a spike level of 0.55 µg/L, verifying the feasibility for the analysis of environmental water samples. This work provides possibilities to investigate the transformation and potential risks of nSe in the environment.

Speciation of Selenium Nanoparticles and Other Selenium Species in Soil: Simple Extraction Followed by Membrane Separation and ICP-MS Determination

The application of selenium nanoparticle (SeNP)-based fertilizers can cause SeNPs to enter the soil environment. Considering the possible transformation of SeNPs and the species-dependent toxicity of selenium (Se), accurate analysis of SeNPs and other Se species present in the soil would help rationally assess the potential hazards of SeNPs to soil organisms. Herein, a novel method for speciation of SeNPs and other Se species in soil was established. Under the optimized conditions, SeNPs, selenite, selenate, and seleno amino acid could be simultaneously extracted from the soil with mixtures of tetrasodium pyrophosphate (5 mM) and potassium dihydrogen phosphate (1.2 μM), while inert Se species (mainly metal selenide) remained in the soil. Then, extracted SeNPs can be effectively captured by a nylon membrane (0.45 μm) and quantified by inductively coupled plasma mass spectrometry (ICP-MS). Other extracted Se species can be separated and quantified by high-performance liquid chromatography coupled with ICP-MS. Based on the difference between the total Se contents and extracted Se contents, the amount of metal selenide can be calculated. The limits of detection of the method were 0.02 μg/g for SeNPs, 0.05 μg/g for selenite, selenate, and selenocystine, and 0.25 μg/g for selenomethionine, respectively. Spiking experiments also showed that our method was applicable to real soil sample analysis. The present method contributes to understanding the speciation of Se in the soil environment and further estimating the occurrence and application risks of SeNPs.

Nanoparticulate pollutants in the environment: Analytical methods, formation, and transformation

The wide application of nanomaterials and plastic products generates a substantial number of nanoparticulate pollutants in the environment. Nanoparticulate pollutants are quite different from their bulk counterparts because of their unique physicochemical properties, which may pose a threat to environmental organisms and human beings. To accurately predict the environmental risks of nanoparticulate pollutants, great efforts have been devoted to developing reliable methods to define their occurrence and track their fate and transformation in the environment. Herein, we summarized representative studies on the preconcentration, separation, formation, and transformation of nanoparticulate pollutants in environmental samples. Finally, some perspectives on future research directions are proposed.

Determination of the Particle Number Concentration, Size Distribution, and Species of Dominant Silver-Containing Nanoparticles in Soils by Single-Particle ICP-MS

The potential risk of various silver-containing nanoparticles (AgCNPs) in soils is related to the concentration, size, and speciation, but their determination remains a great challenge. Herein, we developed an effective method for determining the particle number, size, and species of dominant AgCNPs in soils, including nanoparticles of silver (Ag NPs), silver chloride (AgCl NPs), and silver sulfide (Ag₂S NPs). By ultrasonication wand-assisted tetrasodium pyrophosphate extraction, these AgCNPs were extracted efficiently from soils. Then, multistep selective dissolution of Ag NPs, AgCl NPs, and whole Ag NPs/AgCl NPs/Ag₂S NPs was achieved by 1% (v/v) H₂O₂, 5% (v/v) NH₃·H₂O, and 10 mM thiourea in 2% (v/v) acetic acid, respectively. Finally, the particle number concentration and size distribution of AgCNPs in the extracts and the remaining AgCNP particle number concentration after each dissolution were determined by single-particle inductively coupled plasma mass spectroscopy for speciation of the dominant AgCNPs. AgCNPs were detected in all five soil samples with the concentrations of 0.23-8.00 × 10⁷ particles/g and sizes of 16-110 nm. Ag₂S NPs were the main form of AgCNPs in the examined soils with the percentage range of 53.98-69.19%, followed by AgCl NPs (11.42-23.31%) and Ag NPs (7.78-16.19%). Our method offers a new approach for evaluating the occurrence and potential risk of AgCNPs in environmental soils.

Protein corona-induced extraction coupled to Fenton oxidation for selective and non-destructive preconcentration of Ag2S nanoparticles from waters

Sulfidation of silver nanoparticles (AgNPs) to generate silver sulfide nanoparticles (Ag₂S-NPs) significantly influences their fate and toxicity in natural environments. However, the correlational research in this field was limited by the lack of methods for speciation analysis of Ag₂S-NPs. To address this challenge, a novel protocol for the selective Ag₂S-NP extraction from real waters was developed using protein corona-induced extraction coupled to Fenton oxidation of AgNPs with Fe³⁺/H₂O₂ reagents. The ability of various concentrations of Fe³⁺/H₂O₂ to selectively dissociate AgNPs into ions was first evaluated. Then, selective separation and preconcentration of the remaining Ag₂S-NPs was established by optimizing the parameters that may affect the protein corona-induced extraction efficiency, followed by quantification with inductively coupled plasma mass spectrometry (ICP-MS), enabling an ultrahigh enrichment factor of 10,000 and extremely low detection limit (LOD) of 1.8 ng/L. The presence of humic acid (HA), inorganic salts and particles at the environmentally relevant levels had limited effects on Ag₂S-NP extraction. As demonstrated by transmission electron microscopy (TEM) analysis and single particle ICP-MS (spICP-MS), the sizes, shapes, and compositions of Ag₂S-NPs extracted with the proposed method remain in intact. Good recoveries of 83.7-105% were achieved for the Ag₂S-NPs spiked in four natural waters at the level of 97.8 ng/L. Due to the high yields and applicability to Ag₂S-NPs at environmentally relevant concentrations, this proposed method is particularly suitable to track the generation and transformation of Ag₂S-NPs in various scenarios.

Roadmap of environmental health research on emerging contaminants: Inspiration from the studies on engineered nanomaterials

Research on the environmental health of emerging contaminants is critical to understand their risks before causing severe harm. However, the low environmental concentrations, complex behaviors, and toxicology of emerging contaminants present enormous challenges for researchers. Here, we reviewed the research on the environmental health of engineered nanomaterials (ENMs), one of the typical emerging contaminants, to enlighten pathways for future research on emerging contaminants at their initial exploratory stage. To date, some developed pretreatment methods and detection technologies have been established for the determination of ENMs in natural environments. The mechanisms underlying the transfer and transformation of ENMs have been systematically explored in laboratory studies. The mechanisms of ENMs-induced toxicity have also been preliminarily clarified at genetic, cellular, individual, and short food chain levels, providing not only a theoretical basis for revealing the risk change and environmental health effects of ENMs in natural environments but also a methodological guidance for studying environmental health of other emerging contaminants. Nonetheless, due to the interaction of multiple environmental factors and the high diversity of organisms in natural environments, health effects observed in laboratory studies likely differ from those in natural environments. We propose a holistic approach and mesocosmic model ecosystems to systematically carry out environmental health research on emerging contaminants, obtaining data that determine the objectivity and accuracy of risk assessment.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

New Analytical Approaches for Effective Quantification and Identification of Nanoplastics in Environmental Samples

Nanoplastics (NPs) are a rapidly developing subject that is relevant in environmental and food research, as well as in human toxicity, among other fields. NPs have recently been recognized as one of the least studied types of marine litter, but potentially one of the most hazardous. Several studies are now being reported on NPs in the environment including surface water and coast, snow, soil and in personal care products. However, the extent of contamination remains largely unknown due to fundamental challenges associated with isolation and analysis, and therefore, a methodological gap exists. This article summarizes the progress in environmental NPs analysis and makes a critical assessment of whether methods from nanoparticles analysis could be adopted to bridge the methodological gap. This review discussed the sample preparation and preconcentration protocol for NPs analysis and also examines the most appropriate approaches available at the moment, ranging from physical to chemical. This study also discusses the difficulties associated with improving existing methods and developing new ones. Although microscopical techniques are one of the most often used ways for imaging and thus quantification, they have the drawback of producing partial findings as they can be easily mixed up as biomolecules. At the moment, the combination of chemical analysis (i.e., spectroscopy) and newly developed alternative methods overcomes this limitation. In general, multiple analytical methods used in combination are likely to be needed to correctly detect and fully quantify NPs in environmental samples.

Analytical methods and environmental processes of nanoplastics

The degradation of plastic debris may result in the generation of nanoplastics (NPs). Their high specific surface area for the sorption of organic pollutions and toxic heavy metals and possible transfer between organisms at different nutrient levels make the study of NPs an urgent priority. However, there is very limited understanding on the occurrence, distribution, abundant, and fate of NPs in the environment, partially due to the lack of suitable techniques for the separation and identification of NPs from complex environmental matrices. In this review, we first overviewed the state-of-the-art methods for the extraction, separation, identification and quantification of NPs in the environment. Some of them have been successfully applied for the field determination of NPs, while some are borrowed from the detection of microplastics or engineered nanomaterials. Then the possible fate and transport of NPs in the environment are thoroughly described. Although great efforts have been made during the recent years, large knowledge gaps still exist, such as the relatively high detection limit of existing method failing to detect ultralow masses of NPs in the environment, and spherical polystyrene NP models failing to represent the various compositions of NPs with different irregular shapes, which needs further investigation.