Ligand-Assisted Extraction for Separation and Preconcentration of Gold Nanoparticles from Waters

A new two-step extraction procedure is proposed for separation and preconcentration of gold nanoparticles (Au-NPs) from aqueous samples. First, Au-NPs are loaded onto a reversed phase C-18 (RP-C18) column, and then ligand-assisted extraction into chloroform is performed. 1-Dodecanethiol (1-DDT, 5 mM) was used as selective ligand for quantitative extraction under ultrasonic condition. Parameters of the extraction procedure, such as sample volume, organic solvent, concentration and nature of the ligand, ultrasonication time, pH of the sample, and different coating as well as sizes of Au-NPs were investigated in regard to the extraction efficiency of Au-NPs. The optimized procedure allows separation and preconcentration of the Au-NPs with an enrichment factor of up to 250 assuring no changes in size and/or shape of the NPs. This was proved by investigation of the particles by UV–vis spectrometry and transmission electron microscopy (TEM). Furthermore, the presence of potentially interfering other metal nanoparticles (M-NPs) and dissolved organic matter (DOM) was studied. Observed minor recoveries of Au-NPs in DOM model solutions were overcome by hydrogen peroxide pretreatment up to a DOM concentration of about 4 mg/L. Feasibility of the proposed method was proved by application of the optimized procedure to 5 real water samples. Recoveries of Au-NPs in the real waters spiked in a concentration range from 0.15 to 5100 μg/L obtained by this method varied from 68.4% to 99.4%. Consequently, the proposed approach has great potential for the analysis of M-NPs in environmental waters

Aggregation, Sedimentation and Dissolution of Cu(OH)2-Nanorods-Based Nanopesticide in Soil Solutions

Along with the development of nanotechnology, nanomaterials have been gradually applied to agriculture in recent years, such as Cu(OH)2-nanorods-based nanopesticide, an antibacterial agrochemical with a high efficacy. Nevertheless, knowledge about physical stability of Cu(OH)2 nanopesticide in soil solutions is currently scarce, restricting comprehensive understanding of the fate and risk of Cu(OH)2 nanopesticide in the soil environment. Herein we investigated aggregation, sedimentation and dissolution of Cu(OH)2 nanopesticide in soil solutions extracted from three different soil samples, wherein commercial Cu(OH)2 nanopesticide formulation (NPF), as well as its active ingredient (AI) and laboratory-prepared Cu(OH)2 nanorods (NR) with similar morphology as AI, were used as model Cu(OH)2 nanopesticides. We found that NPF compared to AI showed less extents of aggregation in ultrapure water due to the presence of dispersing agent in NPF. Yet, moderated aggregation and sedimentation were observed for Cu(OH)2 nanopesticide irrespective of NPF, AI or NR when soil solutions were used instead of ultrapure water. The sedimentation rate constants of AI and NPF were 0.023 min−1 and 0.010 min−1 in the ultrapure water, whereas the rate constants of 0.003–0.021 min−1 and 0.002–0.007 min−1 were observed for AI and NPF in soil solutions, respectively. Besides aggregation and sedimentation, dissolution of Cu(OH)2 nanopesticide in soil solutions was highly dependent on soil type, wherein pH and organic matter played important roles in dissolution. Although the final concentrations of dissolved copper (1.08–1.37 mg/L) were comparable among different soil solutions incubating 48 mg/L of AI, NPF or NR for 96 h, a gradual increase followed by an equilibrium was only observed in the soil solution from acidic soil (pH 5.16) with the low content of organic matter (1.20 g/kg). This work would shed light on the fate of Cu(OH)2 nanopesticide in the soil environment, which is necessary for risk assessment of the nanomaterials-based agrochemical

Quantification of Nanoscale Silver Particles Removal and Release from Municipal Wastewater Treatment Plants in Germany

The majority of pure silver nanoparticles in consumer products are likely released into sewer systems and usually end up in wastewater treatment plants (WWTPs). Research investigating the reduction in nanoscale silver particles (n-Ag-Ps) has focused on the biological treatment process, generally in controlled laboratory experiments. This study, analyzing the field-collected samples from nine municipal WWTPs in Germany, is the first to evaluate the reduction in n-Ag-Ps by mechanical and biological treatments in sequence in WWTPs. Additionally, the concentration of n-Ag-Ps in effluent was determined through two different methods that are presented here: novel ionic exchange resin (IER) and cloud point extraction (CPE) methods. The n-Ag-Ps concentrations in influent were all low (<1.5 μg/L) and decreased (average removal efficiency of ∼35%) significantly after mechanical treatment, indicating that the mechanical treatment contributes to the n-Ag-Ps removal. Afterward, more than 72% of the remaining n-Ag-Ps in the semi-treated wastewater (i.e., wastewater after mechanical treatment) were reduced by biological treatment. Together, these processes reduced 95% of the n-Ag-Ps that entered WWTPs, which resulted in low concentration of n-Ag-Ps in the effluents (<12 ng/L). For a WWTP with 520000 t/d treatment capacity, we estimated that the daily n-Ag-Ps load in effluent discharge equated to about 4.4 g/d. Obviously, WWTPs are not potential point sources for n-Ag-Ps in the aquatic environment

Rethinking Stability of Silver Sulfide Nanoparticles (Ag₂S‑NPs) in the Aquatic Environment: Photoinduced Transformation of Ag₂S‑NPs in the Presence of Fe(III)

The stability of engineered nanomaterials in a natural aquatic environment has drawn much attention over the past few years. Silver sulfide nanoparticles (Ag₂S-NPs) are generally assumed to be stable in a natural environment as a result of their physicochemical property; however, it may vary depending upon environmental conditions. Here, we investigated whether and how the environmentally relevant factors including light irradiation, solution pH, inorganic salts, dissolved organic matter (DOM), and dissolved oxygen (DO) individually and in combination influenced the stability of Ag₂S-NPs in an aquatic environment. We presented for the first time that transformation of Ag₂S-NPs can indeed occur in the aqueous system with an environmentally relevant concentration of Fe³⁺ under simulated solar irradiation and natural sunlight within a short time (96 h), along with significant changes in morphology and dissolution. The photoinduced transformation of Ag₂S-NPs in the presence of Fe³⁺ can be dramatically influenced by solution pH, Ca²⁺/Na⁺, Cl^–/SO₄^2–, DOM, and DO. Moreover, Ag₂S-NP dissolution increased within 28 h, followed rapid decline in the next 68 h, which may be a result of the reconstitution of small Ag₂S-NPs. Taken together, this work is of importance to comprehensively evaluate the stability of Ag₂S-NPs in an aquatic environment, improving our understanding of their potential risks to human and environmental health

New Insights into the Stability of Silver Sulfide Nanoparticles in Surface Water: Dissolution through Hypochlorite Oxidation

Silver sulfide nanoparticles (Ag₂SNPs) are considered to be stable in the environment due to the extreme low solubility of Ag₂S (<i>K</i>_sp: 6.3 × 10^–50). Little is known about the stability of Ag₂SNPs in surface water disinfected with aqueous chlorine, one of the globally most used disinfectants. Our results suggested that both uncoated and polyvinylpyrrolidone (PVP)-coated Ag₂SNPs (100 μg/L) underwent dissolution in surface water disinfected with aqueous chlorine at a dose of 4 mg/L, showing the highest dissolved silver ion concentrations of 22.3 and 10.5 μg/L within 45 min, respectively. The natural organic matter (NOM) and dissolved oxygen (DO) posed effects on the Ag₂SNPs dissolution by chlorine; NOM accelerated Ag₂SNPs dissolution while DO reduced the rate and extent of Ag₂SNPs dissolution. We further demonstrated that Ag₂SNPs dissolution was primarily attributed to active oxidative substances including hydroxyl radical and H₂O₂ originating from the hypochlorite oxidation. Additionally, water containing Ag₂SNPs disinfected with hypochlorite showed stronger interference on the zebra fish (<i>Danio rerio</i>) embryo hatching than Ag₂SNPs and hypochlorite on their own. This work documented that Ag₂SNPs could undergo dissolution in surface water through hypochlorite oxidation, posing potential risks to aquatic organisms, and therefore showed new insights into the stability of Ag₂SNPs in natural environment

To What Extent Can Full-Scale Wastewater Treatment Plant Effluent Influence the Occurrence of Silver-Based Nanoparticles in Surface Waters?

Silver-based nanoparticles (Ag-<i>b</i>-NPs) emitted by wastewater treatment plants (WWTPs) are considered to be widely present in the natural environment. However, there is much that is unknown about the effect of WWTP effluent on the occurrence of Ag-<i>b</i>-NPs in surface waters. On the basis of field analysis of representative WWTPs in Germany, we demonstrate that more than 96.4% of Ag-<i>b</i>-NPs from wastewater influent are removed through WWTPs, even though influent contains Ag-<i>b</i>-NP concentrations of tens to hundreds ng L^–1, resulting in effluent Ag-<i>b</i>-NP concentrations of 0.7–11.1 ng L^–1 over the seasons. The estimated flux of Ag-<i>b</i>-NPs associated with WWTPs effluent discharge is ∼33 kg y^–1 in Germany. WWTPs effluent increases Ag-<i>b</i>-NP levels of the River Isar to 2.0–8.6 ng L^–1, while remarkable decreases are observed at sites ∼1.5 km downstream of each discharge point, and Ag-<i>b</i>-NP levels then keep stable (0.9–2.3 ng L^–1) until the next discharge point, showing subtle differences in Ag-<i>b</i>-NP levels between the river and reference lakes without industrial sources and WWTPs effluent discharge. Our results demonstrate that WWTPs effluent can exert a clear influence on the occurrence of Ag-<i>b</i>-NPs in surface waters

Sulfidation as a Natural Antidote to Metallic Nanoparticles Is Overestimated: CuO Sulfidation Yields CuS Nanoparticles with Increased Toxicity in Medaka (<i>Oryzias latipes</i>) Embryos

Sulfidation is considered as a natural antidote to toxicity of metallic nanoparticles (NPs). The detoxification contribution from sulfidation, however, may vary depending on sulfidation mechanisms. Here we present the dissolution–precipitation instead of direct solid-state-shell mechanism to illustrate the process of CuO-NPs conversion to CuS-NPs in aqueous solutions. Accordingly, the CuS-NPs at environmentally relevant concentrations showed much stronger interference on Japanese medaka (<i>Oryzias latipes</i>) embryo hatching than CuO-NPs, which was probably due to elevated free copper ions released from CuS-NPs, leading to significant increase in oxidative stress and causing toxicity in embryos. The larval length was significantly reduced by CuS-NPs, however, no other obviously abnormal morphological features were identified in the hatched larvae. Co-introduction of a metal ion chelator [ethylene diamine tetraacetic acid (EDTA)] could abolish the hatching inhibition induced by CuS-NPs, indicating free copper ions released from CuS-NPs play an important role in hatching interference. This work documents for the first time that sulfidation as a natural antidote to metallic NPs is being overestimated, which has far reaching implications for risk assessment of metallic NPs in aquatic environment