Simultaneous enrichment and speciation of lead and mercury by magnetic solid-phase extraction coupled to HPLC-ICP-MS based on magnetic hydrazine-linked covalent organic frameworks.

BACKGROUND: Trace levels of organic and inorganic lead and mercury species in the environment, including divalent lead (Pb2+), trimethyllead (TML), divalent mercury (Hg2+), monomethylmercury (MeHg), and ethylmercury (EtHg), are highly toxic to humans and ecology. It is of great importance for speciation of lead and mercury to evaluate the toxicity of lead and mercury and their biogeochemistry in the environment. However, simultaneous multi-elemental enrichment and speciation at trace level remains a challenge. There are few reports of simultaneous magnetic solid-phase extraction (MSPE) of organic and inorganic lead and mercury species at trace level in the real water. RESULTS: In this work, a novel core-shell magnetic hydrazine-linked covalent organic frameworks (Fe3O4@COF-TCH) was prepared for the first time by grafting hydrazine-linked COFs on the Fe3O4 nanoparticles. Fe3O4@COF-TCH with abundant thione and imino groups has strong adsorption for lead and mercury species. Based on it, a simple and practical magnetic solid-phase extraction high-performance liquid chromatography-inductively coupled plasma mass spectrometry (MSPE-HPLC-ICP-MS) method was developed for extraction and determination of trace lead and mercury species, including Hg2+, MeHg, EtHg, Pb2+ and TML. The limits of detection (3δ) of the developed method were 0.08, 0.81, 0.90, 0.56 and 0.88 ng L-1 with the enrichment factors (EFs) of 384, 376, 379, 389 and 360-fold for Pb2+, TML, Hg2+, MeHg and EtHg, respectively. The high accuracy and reproducibility have been proved by the spiked recoveries (94.4-103 %) in real samples. SIGNIFICANCE: The proposed method with simple operation and high sensitivity has been successfully applied to simultaneous speciation of lead and mercury at trace levels in the water samples with complicated matrices, including underground water, surface water, sea water. Meanwhile, it has the advantages of cost-saving, labor-saving and time-saving and is suitable for the investigation and risk assessment in water. The development of MSPE-HPLC-ICP-MS method provides ideas and guidance for the simultaneous multi-elemental enrichment and speciation.

Rapid and effective removal of copper, nitrate and trichloromethane from aqueous media by aluminium alloys.

Zero-valent iron (ZVI) has been extensively studied for its efficacy in removing heavy metals, nitrate, and chlorinated organic compounds from contaminated water. However, its limited effectiveness due to rapid passivation and poor selectivity is prompting for alternative solutions, such as the use of aluminium alloys. In this study, the efficacy of five distinct aluminium alloys, namely Al-Mg, Al-Fe, Al-Cu, and Al-Ni, each comprising 50 % Al by mass at a concentration of 10 g/L, was assessed using copper, nitrate and trichloromethane (TCM) as model contaminants. Results show that chemical pollutants reacted immediately with Al-Mg. On the contrary, the remaining three alloys exhibited a delay of 24 h before demonstrating significant reactivity. Remarkably, Al-Mg alloy reduced nitrate exclusively to ammonium, indicating minimal preference for nitrate reduction to N2. In contrast, the Al-Cu, Al-Ni, and Al-Fe alloys exhibited N2 selectivity of 3 %, 5 %, and 19 %, respectively. The removal efficiency of copper, nitrate and TCM reached 99 % within 24 h, 95 % within 48h and 48 % within 48h, respectively. Noteworthy findings included the correlation between Fe concentration within the Al-Fe alloy and an increased N2 selectivity from 9.3 % to 24.1 %. This resulted in an increase of Fe concentration from 10 % to 58 % albeit with a concurrent reduction in reactivity. Cu2+ removal by Al-Fe alloy occurred via direct electron transfer, while the removal of nitrate and TCM was facilitated by atomic hydrogen generated by the alloy's hydrolysis. Intriguingly, nitrate and TCM suppressed Cu2+ reduction, whereas Cu2+ improved nitrate reduction and TCM degradation. These findings demonstrate the great potential of Al-Mg and Al-Fe alloys as highly efficient agents for water remediation.

Rapid, easy and catalyst-free preparation of magnetic thiourea-based covalent organic frameworks at room temperature for enrichment and speciation of mercury with HPLC-ICP-MS.

The complex and cumbersome preparation of magnetic covalent organic frameworks (COFs) nanocomposites on a small scale limits their application. Herein, a rapid and easy route was employed for the preparation of magnetic thiourea-based COFs nanocomposites. COFs were coated on Fe3O4 nanoparticles at room temperature without a catalyst within approximately 30 min. This method is suitable for the large-scale preparation of magnetic adsorbent. Using the as-prepared magnetic adsorbent (Fe3O4@COF-TpTU), we developed a simple, efficient, and sensitive magnetic solid-phase extraction-high performance liquid chromatography-inductively coupled plasma-mass spectrometry (MSPE-HPLC-ICP-MS) for the enrichment and determination of mercury species, including Hg2+, methylmercury (MeHg), and ethylmercury (EtHg). The effects of the experimental parameters on the extraction efficiency, including solution pH, adsorption and desorption time, composition and volume of the elution solvent, salinity, coexisting ions, and dissolved organic matter, were comprehensively investigated. Under optimised conditions, the limits of detection in the developed method were 0.56, 0.34, and 0.47 ng L-1 with enrichment factors of 190, 195, and 180-fold for Hg2+, MeHg, and EtHg, respectively. The satisfactory spiked recoveries (97.0-103%) in real water samples and high consistency between the certified and determined values in a certified reference material demonstrate the high accuracy and reproducibility of the developed method. The as-proposed method with simple operation, high sensitivity, and excellent anti-matrix interference performance was successfully applied to the enrichment and determination of trace levels of mercury species in the natural samples with complicated matrices, such as underground water, surface water, seawater and biological samples.

Highly efficient capture of mercury from complex water matrices by AlZn alloy reduction-amalgamation and in situ layered double hydroxide.

Mercury pollution is a critical, worldwide problem and the efficient, cost-effective removal of mercury from complex, contaminated water matrices in a wide pH range from strongly acidic to alkaline has been a challenge. Here, AlZn and AlFe alloys are investigated and a new process of synergistic reduction-amalgamation and in situ layered double hydroxide (SRA-iLDH) for highly efficient capture of aqueous Hg(II) is developed using AlZn alloys. The parameters include the pH values of 1-12, the Hg(II) concentrations of 10-1000 mg L-1, and the alloy's Zn concentrations of 20%, 50% and 70% and Fe concentrations of 10%, 20% and 50%. The initial rate of Hg(II) uptake by AlZn alloys decreases with increasing Zn concentration while the overall rate is not affected. Specifically, AlZn50 alloy removes >99.5% Hg(II) from 10 mg L-1 solutions at pH 1-12 in 5 min at a rate constant of 0.055 g mg-1 min-1 and achieves a capacity of 5000 mg g-1, being the highest value reported so far. The super-performance of AlZn alloy is attributed to multiple functions of chemical reduction, dual amalgamation, in situ LDH's surface complexation and adsorption, isomorphous substitution and intercalation. This study provides a simple and highly efficient approach for removing Hg(II) from complex water matrices.

Monitoring the Cd2+ release from Cd-containing quantum dots in simulated body fluids by size exclusion chromatography coupled with ICP-MS.

Quantification of Cd2+ release from Cd-containing quantum dots (QDs) is of fundamental importance to elucidate its toxicity to organisms, but remains a great challenge due to the lack of appropriate analytical method. Herein, a facile method based on size exclusion chromatography (SEC) combined with inductively coupled plasma mass spectrometry (ICP-MS) was developed for separating and quantifying the QDs and counterpart ions. By using the mixture of sodium dodecyl sulfate (SDS) and ethylenediaminetetraacetic acid tetrasodium salt (EDTA) as the mobile phase, the defect of QD and ion adsorption onto the SEC column was overcome, thus realizing the accurate quantification of ionic species. Besides, the concentration of QDs was achieved through subtracting the ion concentration from the total concentration. Selecting CdSe@ZnS as the typical QDs, the Cd2+ release process in four typical simulated body fluids, namely, simulated gastric fluid, simulated sweat, Gamble's solution, and artificial lysosomal fluid, was monitored using the developed SEC-ICP-MS method. The media pH is identified as the decisive factor which controls the dissolution of ZnS shells and also the Cd2+ release kinetics and final concentration. Our results suggest that the oral pathway for QD uptake poses the biggest risk to human health.

Groundwater remediation using Magnesium-Aluminum alloys and in situ layered doubled hydroxides.

In situ remediation of groundwater by zerovalent iron (ZVI)-based technology faces the problems of rapid passivation, fast agglomeration, limited range of pollutants and secondary contamination. Here a new concept of Magnesium-Aluminum (Mg-Al) alloys and in situ layered double hydroxides on is proposed for the degradation and removal of a wide variety of inorganic and organic pollutants from groundwater. The Mg-Al alloy provides the electrons for the chemical reduction and/or the degradation of pollutants while released Mg2+, Al3+ and OH- ions react to generate in situ LDH precipitates, incorporating other divalent and trivalent metals and oxyanions pollutants and further adsorbing the micropollutants. The Mg-Al alloy outperforms ZVI for treating acidic, synthetic groundwater samples contaminated by complex chemical mixtures of heavy metals (Cd2+, Cr6+, Cu2+, Ni2+ and Zn2+), nitrate, AsO33-, methyl blue, trichloroacetic acid and glyphosate. Specifically, the Mg-Al alloy achieves removal efficiency ≥99.7% for these multiple pollutants at concentrations ranging between 10 and 50 mg L-1 without producing any secondary contaminants. In contrast, ZVI removal efficiency did not exceed 90% and secondary contamination up to 220 mg L-1 Fe was observed. Overall, this study provides a new alternative approach to develop efficient, cost-effective and green remediation for water and groundwater.

Magnetic solid-phase extraction for speciation of mercury based on thiol and thioether-functionalized magnetic covalent organic frameworks nanocomposite synthesized at room temperature.

A simple and practical magnetic solid-phase extraction high-performance liquid chromatography-inductively coupled plasma mass spectrometry (MSPE-HPLC-ICP-MS) method for extraction and determination of trace mercury species, including inorganic mercury (IHg), monomethylmercury (MeHg) and ethylmercury (EtHg), was developed. The MSPE adsorbent, urchin-like thiol and thioether-functionalized magnetic covalent organic frameworks (Fe3O4@COF-S-SH), was synthesized by coating covalent organic frameworks (COFs) on the surface of Fe3O4 nanoparticles at room temperature and then easily grafting 1,2-Ethanedithiol on the COFs. The as-prepared Fe3O4@COF-S-SH has strong adsorption capacity for IHg, MeHg and EtHg, with excellent static adsorption capacity: 571, 559 and 564 mg g-1, respectively. The parameters influencing the extraction and enrichment had been optimized, including pH, adsorption and desorption time, composition and amount of the eluent, co-existing ions and dissolved organic materials etc. Under the optimized condition, the limit of detection (3δ) of the proposed method were 0.96, 0.17 and 0.47 ng L-1 for IHg, MeHg and EtHg, and the developed method has high actual enrichment factors of 370, 395, 365-fold for IHg, MeHg and EtHg based on 200 mL samples, respectively. The high accuracy and reproducibility has been proved by the spiked recoveries (96.0‒108 %) in real water samples and determination of the certified reference material. Both the adsorption and desorption process can be completed within 5 min. The proposed method with simple operation, short pre-concentration time and high sensitivity has been successfully applied to mercury speciation at trace levels in the samples with complicated matrices, including underground water, surface water, sea water and fish samples.

Simultaneous determination of polybrominated diphenyl ethers and hydroxylated analogues in human serum using high-performance liquid chromatography-inductively coupled plasma mass spectrometry.

Polybrominated diphenyl ethers (PBDEs) and their hydroxylated (OH-BDE) analogues are known as contaminants with potential risks to human health. In this work, a HPLC-ICP-MS method was developed for simultaneous determination of four polybrominated diphenyl ethers (BDE-47, -99, -153 and -209) and four hydroxylated analogues (3-OH-BDE-47, 5-OH-BDE-47, 6-OH-BDE-47, 5'-OH-BDE-99) in human serum. Solid-phase extraction (SPE) was employed as the primary extraction and purification procedure. By using mixtures of acetone and hexane with different rations, OH-PBDEs and PBDEs were efficiently recovered during elution procedure. With additional ultrasonic assisted extraction of PBDEs from solid residue after protein precipitation, the recoveries of investigated analytes ranged from 79.1 %to 89.9%. Due to the characteristics of inductively coupled plasma (ICP), organic matrix effects were effectively eliminated. Good sensitivity and precision were also obtained. The limits of quantification ranged from 0.060 to 0.081 ng mL-1 and inter-/intra-day relative standard deviations were all below 4%. In addition, compound-independent calibration (CIC) was investigated and the spray chamber efficiency might be a key factor for CIC application among different kinds of brominated chemicals. Finally, the developed method was successfully applied for analysis of 20 human serum samples collected from the Tianjin city. This work provided an alternative approach for simultaneous determination of halogenated chemicals by quantification of halogen element with one-time pretreatment, especially for human serum samples with limited sample volume.

Ratiometric fluorescence immunoassay based on FAM-DNA-functionalized CdSe/ZnS QDs for the sensitive detection of tetrabromobisphenol A in foodstuff and the environment.

A simple indirectly competitive ratiometric fluorescent immunoassay was designed based on fluorescein amidite (FAM)-DNA-functionalized CdSe/ZnS quantum dots (QDs) for the sensitive determination of tetrabromobisphenol A (TBBPA). At the detection system, catalase (CAT) was labeled on the secondary antibody (Ab2), which served as a controller of the H2O2 concentration. After the competitive binding step, the emitted red fluorescence (excitation at 490 nm) from FAM-DNA-functionalized CdSe/ZnS QDs could be effectively quenched by the H2O2 added. Under the optimized conditions, the limit of detection (LOD) reached 0.118 µg/L with a linear range of 0.34-45.34 µg/L, which was approximately 1 order of magnitude lower than that by HRP-based traditional ELISA. Furthermore, the combination of the dual-output ratiometric fluorescence assays with ELISA improved the inherent built-in rectification to the environment, which brought about satisfactory accuracy and precision (recoveries, 83.16-112.4%; CV, 2.42-7.28%), indicating great potential for the determination of trace TBBPA from food and environmental samples. Graphical abstract.

Quantification of Trace Mercury in Water: Solving the Problem of Adsorption, Sample Preservation, and Cross-Contamination.

Adsorption, sample preservation, and cross-contamination are the major impediments to the accurate and sensitive analysis of low-level mercury samples. Common measures to deal with this issue are to use Teflon, quartz, or borosilicate glass bottles for sampling, standard solution and sample preservation with oxidative chemicals, to prepare standard solutions daily and to use dedicated glassware. This paper demonstrates that these measures are neither efficient nor effective. Two common laboratory sample containers (borosilicate volumetric glass flasks and polypropylene tubes) are investigated for the preparation and preservation of water samples and standard solutions of 0.2-1 µg L-1 with 2% HNO3. Mercury adsorption rates of 6-22% are observed within 30 min and after 48 days, the adsorption is greater than 98%. In stark contrast, no adsorption is found during a testing period of 560 days when the solutions are subject to potassium permanganate-persulfate digestion. New glass flasks and polypropylene bottles are free of mercury contamination but reused flasks are a major source of mercury cross-contamination. To minimize adsorption and cross-contamination, standard solutions are treated by potassium permanganate-persulfate or BrCl digestion, and each individual sample and standard solution should be stored and prepared in single-use polypropylene bottle, without transference.

Simultaneous removal of nitrate, copper and hexavalent chromium from water by aluminum-iron alloy particles.

Groundwater contamination is a worldwide concern and the development of new materials for groundwater remediation has been of great interest. This study investigated removal kinetics and mechanisms of nitrate, copper ion and hexavalent chromium (20-50 mg L-1) by particles of Al-Fe alloy consisting of 20% Fe in batch reactors from a single KNO3, CuSO4, Cu(NO3)2, K2Cr2O7 and their mixed solutions. The effects of contaminant interactions and initial pH of the solution were examined and the alloy particles before and after reaction were characterized by X-ray diffraction spectrometer, scanning electron microscopy and X-ray photoelectron spectroscopy. The removal mechanisms were attributed to chemical reduction [Cu(II) to Cu, NO3- to NH3 and Cr(VI) to Cr(III)] and co-precipitation of Cr(III)-Al(III)-Fe(III) hydroxides/oxyhydroxides. Cu(II) enhanced the rates of NO3- and Cr(VI) reduction and Cr(VI) was an inhibitor for Cu(II) and NO3- reduction. This study demonstrates that Al-Fe alloy is of potential for groundwater remediation.

Accurate Determination of Trace Molybdenum in Drinking Water by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry.

A method for accurate and precise determination of trace molybdenum in drinking water by isotope dilution inductively coupled plasma mass spectrometry was developed, given the concentrations of Mo in drinking-water samples from Chaoyang and Changping districts of Beijing (China) as 1.017 ± 0.008 and 1.033 ± 0.007 µg kg-1 (k = 2), respectively. Special care was taken for the validation of the proposed ID-ICPMS method using CRM 7203-a, a certified reference material for elemental analysis of tap water.

Nitrate reduction in water by aluminum alloys particles.

Nano zero-valent iron (NZVI) particles have been extensively investigated for nitrate reduction in water. However, the reduction by NZVI requires acidic pH conditions and the final product is exclusively ammonium, leading to secondary contamination. In addition, nanomaterials have potential threats to environment and the transport and storage of nanomaterials are of safety concerns. Aluminum, the most abundant metal element in the earth's crust, is able to reduce nitrate, but the passivation of aluminum limits its application. Here we report Al alloys (85% Al) with Fe, Cu or Si for aqueous nitrate reduction. The Al alloys particles of 0.85-0.08 mm were inactivate under ambient conditions and a simple treatment with warm water (45 °C) quickly activated the alloy particles for rapid reduction of nitrate. The Al-Fe alloy particles at a dosage of 5 g/L rapidly reduced 50 mg-N/L nitrate at a reaction rate constant (k) of 3.2 ± 0.1 (mg-N/L)1.5/min between pH 5-6 and at 4.0 ± 0.1 (mg-N/L)1.5/min between pH 9-11. Dopping Cu in the Al-Fe alloy enhanced the rates of reduction whereas dopping Si reduced the reactivity of the Al-Fe alloy. The Al alloys converted nitrate to 20% nitrogen and 80% ammonium. Al in the alloy particles provided electrons for the reduction and the intermetallic compounds in the alloys were likely to catalyze nitrate reduction to nitrogen.

Dispersive liquid-liquid microextraction of silver nanoparticles in water using ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate.

Using the ionic liquid (IL) 1-octyl-3-methylimidazolium hexafluorophosphate as the extractant and methanol as the dispersion solvent, a dispersive liquid-liquid microextraction method was developed to extract silver nanoparticles (AgNPs) from environmental water samples. Parameters that influenced the extraction efficiency such as IL concentration, pH and extraction time were optimized. Under the optimized conditions, the highest extraction efficiency for AgNPs was above 90% with an enrichment factor of >90. The extracted AgNPs in the IL phase were identified by transmission electron microscopy and ultraviolet-visible spectroscopy, and quantified by inductively coupled plasma mass spectrometry after microwave digestion, with a detection limit of 0.01µg/L. The spiked recovery of AgNPs was 84.4% with a relative standard deviation (RSD) of 3.8% (n=6) at a spiked level of 5µg/L, and 89.7% with a RSD of 2.2% (n=6) at a spiked level of 300µg/L, respectively. Commonly existed environmental ions had a very limited influence on the extraction efficiency. The developed method was successfully applied to the analysis of AgNPs in river water, lake water, and the influent and effluent of a wastewater treatment plant, with recoveries in the range of 71.0%-90.9% at spiking levels of 0.11-4.7µg/L.

Speciation Analysis of Labile and Total Silver(I) in Nanosilver Dispersions and Environmental Waters by Hollow Fiber Supported Liquid Membrane Extraction.

Hollow fiber supported liquid membrane (HFSLM) extraction was coupled with ICP-MS for speciation analysis of labile Ag(I) and total Ag(I) in dispersions of silver nanoparticles (AgNPs) and environmental waters. Ag(I) in aqueous samples was extracted into the HFSLM of 5%(m/v) tri-n-octylphosphine oxide in n-undecane, and stripped in the acceptor of 10 mM Na2S2O3 and 1 mM Cu(NO3)2 prepared in 5 mM NaH2PO4-Na2HPO4 buffer (pH 7.5). Negligible depletion and exhaustive extraction were conducted under static and 250 rpm shaking to extract the labile Ag(I) and total Ag(I), respectively. The extraction equilibration was reached in 8 h for both extraction modes. The extraction efficiency and detection limit were (2.97 ± 0.25)% and 0.1 µg/L for labile Ag(I), and (82.3 ± 2.0)% and 0.5 µg/L for total Ag(I) detection, respectively. The proposed method was applied to determine labile Ag(I) and total Ag(I) in different sized AgNP dispersions and real environmental waters, with spiked recoveries of total Ag(I) in the range of 74.0-98.1%. With the capability of distinguishing labile and total Ag(I), our method offers a new approach for evaluating the bioavailability and understanding the fate and toxicity of AgNPs in aquatic systems.

Exposure medium: key in identifying free Ag+ as the exclusive species of silver nanoparticles with acute toxicity to Daphnia magna.

It is still not very clear what roles the various Ag species play in the toxicity of silver nanoparticles (AgNPs). In this study, we found that traditional exposure media result in uncontrollable but consistent physicochemical transformation of AgNPs, causing artifacts in determination of median lethal concentration (LC50) and hindering the identification of Ag species responsible for the acute toxicity of AgNPs to Daphnia magna. This obstacle was overcome by using 8 h exposure in 0.1 mmol L(-1) NaNO3 medium, in which we measured the 8-h LC50 of seven AgNPs with different sizes and coatings, and determined the concentrations of various Ag species. The LC50 as free Ag(+) of the seven AgNPs (0.37-0.44 µg L(-1)) agreed very well with that of AgNO3 (0.40 µg L(-1)), and showed the lowest value compared to that as total Ag, total Ag(+), and dissolved Ag, demonstrating free Ag(+) is exclusively responsible for the acute toxicity of AgNPs to D. magna, while other Ag species in AgNPs have no contribution to the acute toxicity. Our results demonstrated the great importance of developing appropriate exposure media for evaluating risk of nanomaterials.

Photoreduction and stabilization capability of molecular weight fractionated natural organic matter in transformation of silver ion to metallic nanoparticle.

Photoinduced reduction of silver ion (Ag(+)) to silver nanoparticles (AgNPs) by dissolved organic matter (DOM) plays a crucial role in the transformation and transport of engineered AgNPs and Ag(+) in aquatic environments. DOM is a mixture of natural polymers with wide molecular weight (MW) distribution, and the roles of specific components of DOM in the photoreduction of Ag(+) to AgNPs are still not understood. In this study, MW fractionated natural organic matter (Mf-NOM) were investigated for their roles on the photoreduction process and stabilization of the formed AgNPs. This photoinduced reduction process depends highly on pH, concentration of Ag(+) and NOM, light quality, and the MW of Mf-NOM. Monochromatic radiation and light attenuation correction suggested that the difference of Mf-NOM on reduction was mainly ascribed to the differential light attenuation of Mf-NOM rather than the "real" reductive ability. More importantly, compared with low MW fractions, the high MW Mf-NOMs exhibit drastically higher capability in stabilizing the photosynthesized AgNPs against Ca(2+)-induced aggregation. This finding is important for a better understanding of the differential roles of Mf-NOM in the transformation and transport of Ag(+) and engineered AgNPs in DOM-rich surface water.

Highly dynamic PVP-coated silver nanoparticles in aquatic environments: chemical and morphology change induced by oxidation of Ag(0) and reduction of Ag(+).

The fast growing and abundant use of silver nanoparticles (AgNPs) in commercial products alerts us to be cautious of their unknown health and environmental risks. Because of the inherent redox instability of silver, AgNPs are highly dynamic in the aquatic system, and the cycle of chemical oxidation of AgNPs to release Ag(+) and reconstitution to form AgNPs is expected to occur in aquatic environments. This study investigated how inevitable environmentally relevant factors like sunlight, dissolved organic matter (DOM), pH, Ca(2+)/Mg(2+), Cl(-), and S(2-) individually or in combination affect the chemical transformation of AgNPs. It was demonstrated that simulated sunlight induced the aggregation of AgNPs, causing particle fusion or self-assembly to form larger structures and aggregates. Meanwhile, AgNPs were significantly stabilized by DOM, indicating that AgNPs may exist as single particles and be suspended in natural water for a long time or delivered far distances. Dissolution (ion release) kinetics of AgNPs in sunlit DOM-rich water showed that dissolved Ag concentration increased gradually first and then suddenly decreased with external light irradiation, along with the regeneration of new tiny AgNPs. pH variation and addition of Ca(2+) and Mg(2+) within environmental levels did not affect the tendency, showing that this phenomenon was general in real aquatic systems. Given that a great number of studies have proven the toxicity of dissolved Ag (commonly regarded as the source of AgNP toxicity) to many aquatic organisms, our finding that the effect of DOM and sunlight on AgNP dissolution can regulate AgNP toxicity under these conditions is important. The fact that the release of Ag(+) and regeneration of AgNPs could both happen in sunlit DOM-rich water implies that previous results of toxicity studies gained by focusing on the original nature of AgNPs should be reconsidered and highlights the necessity to monitor the fate and toxicity of AgNPs under more environmentally relevant conditions.

Quantification of the uptake of silver nanoparticles and ions to HepG2 cells.

The toxic mechanism of silver nanoparticles (AgNPs) is still debating, partially because of the common co-occurrence and the lack of methods for separation of AgNPs and Ag(+) in biological matrices. For the first time, Triton-X 114-based cloud point extraction (CPE) was proposed to separate AgNPs and Ag(+) in the cell lysates of exposed HepG2 cells. Cell lysates were subjected to CPE after adding Na2S2O3, which facilitated the transfer of AgNPs into the nether Triton X-114-rich phase by salt effect and the preserve of Ag(+) in the upper aqueous phase through the formation of hydrophilic complex. Then the AgNP and Ag(+) contents in the exposed cells were determined by ICP-MS after microwave digestion of the two phases, respectively. Under the optimized conditions, over 67% of AgNPs in cell lysates were extracted into the Triton X-114-rich phase while 94% of Ag(+) remained in the aqueous phase, and the limits of detection for AgNPs and Ag(+) were 2.94 µg/L and 2.40 µg/L, respectively. This developed analytical method was applied to quantify the uptake of AgNPs to the HepG2 cells. After exposure to 10 mg/L AgNPs for 24 h, about 67.8 ng Ag were assimilated per 10(4) cells, in which about 10.3% silver existed as Ag(+). Compared to the pristine AgNPs (with 5.2% Ag(+)) for exposure, the higher ratio of Ag(+) to AgNPs in the exposed cells (10.3% Ag(+)) suggests the transformation of AgNPs into Ag(+) in the cells and/or the higher uptake rate of Ag(+) than that of AgNPs. Given that the toxicity of Ag(+) is much higher than that of AgNPs, the substantial content of Ag(+) in the exposed cells suggests that the contribution of Ag(+) should be taken into account in evaluating the toxicity of AgNPs to organisms, and previous results obtained by regarding the total Ag content in organisms as AgNPs should be reconsidered.

Speciation analysis of silver nanoparticles and silver ions in antibacterial products and environmental waters via cloud point extraction-based separation.

The rapid growth in commercial use of silver nanoparticles (AgNPs) will inevitably increase silver exposure in the environment and the general population. As the fate and toxic effects of AgNPs is related to the Ag(+) released from AgNPs and the transformation of Ag(+) into AgNPs, it is of great importance to develop methods for speciation analysis of AgNPs and Ag(+). This study reports the use of Triton X-114-based cloud point extraction as an efficient separation approach for the speciation analysis of AgNPs and Ag(+) in antibacterial products and environmental waters. AgNPs were quantified by determining the Ag content in the Triton X-114-rich phase with inductively coupled plasma mass spectrometry (ICPMS) after microwave digestion. The concentration of total Ag(+), which consists of the AgNP adsorbed, the matrix associated, and the freely dissolved, was obtained by subtracting the AgNP content from the total silver content that was determined by ICPMS after digestion. The limits of quantification (S/N = 10) for antibacterial products were 0.4 µg/kg and 0.2 µg/kg for AgNPs and total silver, respectively. The reliable quantification limit was 3 µg/kg for total Ag(+). The presence of Ag(+) at concentrations up to 2-fold that of AgNPs caused no effects on the determination of AgNPs. In the cloud point extraction of AgNPs in antibacterial products, the spiked recoveries of AgNPs were in the range of 71.7-103% while the extraction efficiencies of Ag(+) were in the range of 1.2-10%. The possible coextracted other silver containing nanoparticles in the cloud point extraction of AgNPs were distinguished by transmission electron microscopy (TEM), scanning electron microscopy (SEM)- energy dispersive spectroscopy (EDS), and UV-vis spectrum. Real sample analysis indicated that even though the manufacturers claimed nanosilver products, AgNPs were detected only in three of the six tested antibacterial products.