Nanoenabled foliar-applied agrochemicals can potentially be safer and more efficient than conventional products. However, limited understanding about how nanoparticle properties influence their ...interactions with plant leaves, uptake, translocation through the mesophyll to the vasculature, and transport to the rest of the plant prevents rational design. This study used a combination of Au quantification and spatial analysis to investigate how size (3, 10, or 50 nm) and coating chemistry (PVP versus citrate) of gold nanoparticles (AuNPs) influence these processes. Following wheat foliar exposure to AuNPs suspensions (∼280 ng per plant), adhesion on the leaf surface was increased for smaller sizes, and PVP-AuNPs compared to citrate-AuNPs. After 2 weeks, there was incomplete uptake of citrate-AuNPs with some AuNPs remaining on the outside of the cuticle layer. However, the fraction of citrate-AuNPs that had entered the leaf was translocated efficiently to the plant vasculature. In contrast, for similar sizes, virtually all of the PVP-AuNPs crossed the cuticle layer after 2 weeks, but its transport through the mesophyll cells was lower. As a consequence of PVP-AuNP accumulation in the leaf mesophyll, wheat photosynthesis was impaired. Regardless of their coating and sizes, the majority of the transported AuNPs accumulated in younger shoots (10–30%) and in roots (10–25%), and 5–15% of the NPs <50 nm were exuded into the rhizosphere soil. A greater fraction of larger sizes AuNPs (presenting lower ζ potentials) was transported to the roots. The key hypotheses about the NPs physical–chemical and plant physiology parameters that may matter to predict leaf-to-rhizosphere transport are also discussed.
Engineered nanoparticles (NPs) released into natural environments will interact with natural organic matter (NOM) or humic substances, which will change their fate and transport behavior. ...Quantitative predictions of the effects of NOM are difficult because of its heterogeneity and variability. Here, the effects of six types of NOM and molecular weight fractions of each on the aggregation of citrate-stabilized gold NPs are investigated. Correlations of NP aggregation rates with electrophoretic mobility and the molecular weight distribution and chemical attributes of NOM (including UV absorptivity or aromaticity, functional group content, and fluorescence) are assessed. In general, the >100 kg/mol components provide better stability than lower molecular weight components for each type of NOM, and they contribute to the stabilizing effect of the unfractionated NOM even in small proportions. In many cases, unfractionated NOM provided better stability than its separated components, indicating a synergistic effect between the high and low molecular weight fractions for NP stabilization. Weight-averaged molecular weight was the best single explanatory variable for NP aggregation rates across all NOM types and molecular weight fractions. NP aggregation showed poorer correlation with UV absorptivity, but the exponential slope of the UV–vis absorbance spectrum was a better surrogate for molecular weight. Functional group data (including reduced sulfur and total nitrogen content) were explored as possible secondary parameters to explain the strong stabilizing effect of a low molecular weight Pony Lake fulvic acid sample to the gold NPs. These results can inform future correlations and measurement requirements to predict NP attachment in the presence of NOM.
Predicting nanoparticle fate in aquatic environments requires mimicking of ecosystem complexity to observe the geochemical processes affecting their behaviour. Here, 12 nm Au nanoparticles were added ...weekly to large-scale freshwater wetland mesocosms. After six months, ~70% of Au was associated with the macrophyte Egeria densa, where, despite the thermodynamic stability of Au
in water, the pristine Au
nanoparticles were fully oxidized and complexed to cyanide, hydroxyls or thiol ligands. Extracted biofilms growing on E. densa leaves were shown to dissolve Au nanoparticles within days. The Au biodissolution rate was highest for the biofilm with the lowest prevalence of metal-resistant taxa but the highest ability to release cyanide, known to promote Au
oxidation and complexation. Macrophytes and the associated microbiome thus form a biologically active system that can be a major sink for nanoparticle accumulation and transformations. Nanoparticle biotransformation in these compartments should not be ignored, even for nanoparticles commonly considered to be stable in the environment.
Silver-enabled fabrics may be transformed during use in ways that may affect their release characteristics and antibacterial efficacy. Here, we assess how chemical transformations of silver in ...fabrics treated with Ag nanoparticles or AgCl particles, or containing interwoven Ag0 fibers affect silver leaching and their antibacterial efficacy under different use and end-of-life scenarios. Fabrics were exposed to artificial sweat (use phase) or artificial landfill leachate (sodium chloride, sodium sulfide, or acetic acid; end of life phase). Chemical transformations induced by exposure to sodium chloride, sodium sulfide and acetic acid result in variations in Ag release and corresponding changes in bactericidal properties of the Ag-treated textiles. Exposure to solutions containing chloride ions (sodium chloride and artificial sweat) generally increased leaching compared to deionized water. Conversely, exposure to sodium sulfide and acetic acid solutions decreased Ag release. Exposure to artificial sweat did not affect antibacterial efficacy for fabrics with greater than ~10 μg Ag (g fabric)−1. Sulfide solution exposure decreased antibacterial performance for all but the 500 μg Ag (g fabric)−1. The lower efficacy was consistent with chemical transformation of elemental Ag to AgCl/Ag0 or Ag2S, respectively for chloride and sulfide exposure. AgCl-coated fabrics were more resilient to chemical attack than Ag0-enabled fabrics. These results indicate that fabrics with as low as ~10 μg Ag (g fabric)−1 can maintain high antibacterial efficacy under normal use phase conditions, but below this concentration efficacy significantly decreases. Taken together, the data permit a comparison of the benefits (antimicrobial efficacy) in the context of the impacts (silver release) and inform selection and design of materials and loadings that give the best overall lifecycle benefit.
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•Chemical transformations in Ag-treated textiles caused different Ag release and related changes in bactericidal properties.•Exposure to solutions with chloride ions (NaCl and artificial sweat) generally increased leaching compared to DI water.•Conversely, exposure to Na2S and acetic acid solutions decreased Ag release.•Fabrics with as low as ~10 μg Ag (g fabric)-1 can maintain high antibacterial efficacy.
Nanoparticle (NP) physiochemical properties, including surface charge, affect cellular uptake, translocation, and tissue localization. To evaluate the influence of surface charge on NP uptake by ...plants, wheat seedlings were hydroponically exposed to 20 mg/L of ∼4 nm CeO2 NPs functionalized with positively charged, negatively charged, and neutral dextran coatings. Fresh, hydrated roots and leaves were analyzed at various time points over 34 h using fluorescence X-ray absorption near-edge spectroscopy to provide laterally resolved spatial distribution and speciation of Ce. A 15–20% reduction from Ce(IV) to Ce(III) was observed in both roots and leaves, independent of NP surface charge. Because of its higher affinity with negatively charged cell walls, CeO2(+) NPs adhered to the plant roots the strongest. After 34 h, CeO2(−), and CeO2(0) NP exposed plants had higher Ce leaf concentrations than the plants exposed to CeO2(+) NPs. Whereas Ce was found mostly in the leaf veins of the CeO2(−) NP exposed plant, Ce was found in clusters in the nonvascular leaf tissue of the CeO2(0) NP exposed plant. These results provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs, and suggest that NP coatings can be designed to target NPs to specific parts of plants.
Hydraulic fracturing of unconventional hydrocarbon resources involves the sequential injection of a high-pressure, particle-laden fluid with varying pH’s to make commercial production viable in low ...permeability rocks. This process both requires and produces extraordinary volumes of water. The water used for hydraulic fracturing is typically fresh, whereas “flowback” water is typically saline with a variety of additives which complicate safe disposal. As production operations continue to expand, there is an increasing interest in treating and reusing this high-salinity produced water for further fracturing. Here we review the relevant transport and geochemical properties of shales, and critically analyze the impact of water chemistry (including produced water) on these properties. We discuss five major geochemical mechanisms that are prominently involved in the temporal and spatial evolution of fractures during the stimulation and production phase: shale softening, mineral dissolution, mineral precipitation, fines migration, and wettability alteration. A higher salinity fluid creates both benefits and complications in controlling these mechanisms. For example, higher salinity fluid inhibits clay dispersion, but simultaneously requires more additives to achieve appropriate viscosity for proppant emplacement. In total this review highlights the nuances of enhanced hydrogeochemical shale stimulation in relation to the choice of fracturing fluid chemistry.
Mineral precipitation due to reactions with injected fluids during unconventional fracture stimulation is a well-recognized problem. The goal of this study is to evaluate secondary mineral ...precipitation and permeability attenuation under chemical injection scenarios specific to the Delaware basin. Whole cylindrical cores (2.54 cm diameter and 2.54 cm height) and ground shale (150–250 μm) from the carbonate-rich Bone Spring Formation, Delaware Basin TX (Leonardian), were reacted at 80 °C and 85 bar using a hydraulic fracturing fluid (HFF) recipe and an injection sequence typical of the Delaware Basin. The reacted shales and solutions were analyzed using a variety of laboratory- and synchrotron-based techniques to characterize both the chemical and spatial distributions of secondary mineral precipitation and identify changes in permeability and mineralogy. This carbonate-rich shale (>84% calcite) rapidly neutralized the acidic HFF. Synchrotron-based X-ray fluorescence mapping coupled with X-ray absorption spectroscopy (both bulk and micro) showed that most of the iron was in an oxidized form prior to exposure to HFF and that almost all iron(II) became fully oxidized after the reaction. Scanning electron microscopy images of the ground shale samples primarily identified iron(oxyhydr)oxide microcrystals on grain surfaces. A few small isolated iron-rich areas also contained sulfur, suggesting that some pyrite was preserved when isolated within a calcite crystal but that most was oxidized. The rapid neutralization of the acid spearhead in these carbonate-rich samples demonstrates that the acid spearhead is useful for initiating fractures in extremely calcite-rich rocks but does little to enhance rock permeability. This suggests that the impact of the acid spearhead is significantly smaller for carbonate-rich shales compared to clay-rich shales, which has broad implications for acidizing in carbonate-rich shale formations and iron transformations within these shales.
Deep subsurface stimulation processes often promote fluid-rock interactions that can lead to the formation of small colloidal particles that are suspected to migrate through the rock matrix, ...partially or fully clog pores and microfractures, and promote the mobilization of contaminants. Thus, the goal of this work is to understand the geochemical changes of the host rock in response to reservoir stimulation that promote the formation and migration of colloids. Two different carbonate-rich shales were exposed to different solution pHs (pH = 2 and 7). Iron and other mineral transformations at the shale-fluid interface were first characterized by synchrotron-based XRF mapping. Then, colloids that were able to migrate from the shale into the bulk fluid were characterized by synchrotron-based extended X-ray absorption structure (EXAFS), scanning electron microscopy (SEM), and single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS). When exposed to the pH = 2 solution, extensive mineral dissolution and secondary precipitation was observed; iron-(oxyhydr)oxide colloids colocated with silicates were observed by SEM at the fluid-shale interfaces, and the mobilization of chromium and nickel with these iron colloids into the bulk fluid was detected by sp-icpTOF-MS. Iron EXAFS spectra of the solution at the shale-fluid interface suggests the rapid (within minutes) formation of ferrihydrite-like nanoparticles. Thus, we demonstrate that the pH neutralization promotes the mobilization of existing silicate minerals and the rapid formation of new iron colloids. These Fe colloids have the potential to migrate through the shale matrix and mobilize other heavy metals (such as Cr and Ni, in this study) and impacting groundwater quality, as well produced waters from these hydraulic fracturing operations.
Utilization of nanoparticles (NP) in agriculture as fertilizers or pesticides requires an understanding of the NP properties influencing their interactions with plant roots. To evaluate the influence ...of the solubility of Cu-based NP on Cu uptake and NP association with plant roots, wheat seedlings were hydroponically exposed to 1 mg/L of Cu NPs with different solubilities CuO, CuS, and Cu(OH)2 for 1 h then transferred to a Cu-free medium for 48 h. Fresh, hydrated roots were analyzed using micro X-ray fluorescence (μ-XRF) and imaging fluorescence X-ray absorption near edge spectroscopy (XANES imaging) to provide laterally resolved distribution and speciation of Cu in roots. Higher solubility Cu(OH)2 NPs provided more uptake of Cu after 1 h of exposure, but the lower solubility materials (CuO and CuS) were more persistent on the roots and continued to deliver Cu to plant leaves over the 48 h depuration period. These results demonstrate that NPs, by associating to the roots, have the potential to play a role in slowly providing micronutrients to plants. Thus, tuning the solubility of NPs may provide a long-term slow delivery of micronutrients to plants and provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs.
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