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Here, isotopically labeled 68 ZnO NPs (ZnO NPs) and 68 ZnO NPs with a thin 68 Zn 3 (PO 4 ) 2 shell (ZnO_Ph NPs) were foliarly applied (40 μg Zn) to pepper plants ( Capsicum annuum ) to determine the effect of surface chemistry of ZnO NPs on the Zn uptake and systemic translocation to plant organs over 6 weeks. Despite similar dissolution of both Zn-based NPs after 3 weeks, the Zn 3 (PO 4 ) 2 shell on ZnO_Ph NPs (48 ± 12 nm; -18.1 ± 0.6 mV) enabled a leaf uptake of 2.31 ± 0.34 μg of Zn, which is 2.7 times higher than the 0.86 ± 0.18 μg of Zn observed for ZnO NPs (26 ± 8 nm; 14.6 ± 0.4 mV). Further, ZnO_Ph NPs led to higher Zn mobility and phloem loading, while Zn from ZnO NPs was stored in the epidermal tissues, possibly through cell wall immobilization as a storage strategy. These differences led to higher translocation of Zn from the ZnO_Ph NPs within all plant compartments. ZnO_Ph NPs were also more persistent as NPs in the exposed leaf and in the plant stem over time. As a result, the treatment of ZnO_Ph NPs induced significantly higher Zn transport to the fruit than ZnO NPs. As determined by spICP-TOFMS, Zn in the fruit was not in the NP form. These results suggest that the Zn 3 (PO 4 ) 2 shell on ZnO NPs can help promote the transport of Zn to pepper fruits when foliarly applied. This work provides insight into the role of Zn 3 (PO 4 ) 2 on the surface of ZnO NPs in foliar uptake and in planta biodistribution for improving Zn delivery to edible plant parts and ultimately improving the Zn content in food for human consumption.

Finding and quantifying engineered nanomaterials (ENMs) in soil are challenging because of the abundance of natural nanomaterials (NNMs) with the same elemental composition, for example, TiO 2 . Isotopically enriched ENMs may be distinguished from NNMs with the same elemental composition using single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOF-MS) to measure multiple isotopes simultaneously within each ENM and NNM in soil, but the minimum isotope enrichment needed for detection of ENMs in soil is not known. Here, we determined the isotope enrichment needed for 47 Ti-enriched TiO 2 ENMs to be detectable in soil and assessed the effects of weathering on those requirements for less soluble TiO 2 and more soluble CuO ENMs. The isotope-enriched ENMs were dosed into two different soils and were extracted and measured by spICP-TOF-MS after 1, 7, and 30 days. Isotope-enriched ENMs were recovered and detected for all three time points. The 47 Ti-enriched TiO 2 ENMs were detectable in Lufa 2.2 soil at a nominal dosed concentration of 10 mg-TiO 2 kg -1 which is an environmentally relevant concentration in biosolid-amended soils. For distinguishing an ∼70 nm diameter TiO 2 ENM from TiO 2 NNMs in Lufa 2.2 soil, an ∼10 wt % 47 Ti isotope-enrichment was required, and this enrichment requirement increases as the particle size decreases. This study is the first to evaluate the tracking ability of isotope-enriched ENMs at an individual particle level in soil and provides guidance on the isotope enrichment requirements for quantification of ENMs made from Earth-abundant elements in soils.

Identifying engineered nanomaterials (ENMs) made from earth-abundant elements in soils is difficult because soil also contains natural nanomaterials (NNMs) containing similar elements. Here, machine learning models using elemental fingerprints and mass distributions of three TiO 2 ENMs and Ti-based NNMs recovered from three natural soils measured by single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) was used to identify TiO 2 ENMs in soil. Synthesized TiO 2 ENMs were unassociated with other elements (>98%), while 40% of Ti-based ENM particles recovered from wastewater sludge had distinguishable elemental associations. All Ti-based NNMs extracted from soil had a similar chemical fingerprint despite the soils being from different regions, and >60% of Ti-containing NNMs had no measurable associated elements. A machine learning model best distinguished NNMs and ENMs when differences in Ti-mass distribution existed between them. A trained LR model could classify 100 nm TiO 2 ENMs at concentrations of 150 mg kg -1 or greater. The presence of TiO 2 ENMs in soil could be confirmed using this approach for most ENM-soil combinations, but the absence of a unique chemical fingerprint in a large fraction of both TiO 2 ENMs and Ti-NNMs increases model uncertainty and hinders accurate quantification.

Particle-specific properties, including size and chemical speciation, affect the reactivity of mercury (Hg) in natural systems (e.g., dissolution or methylation). Here, terrestrial, river, and marine sediments were size-fractionated and characterized to correlate particle-specific properties of Hg-bearing solids with their bioavailability potential and measured biomethylation. Marine sediments contained ∼20-50% of the total Hg in the <0.5 μm size fraction, compared to only 0.5 and 3.0% in this size fraction for terrestrial and river sediments, respectively. X-ray absorption spectroscopy (XAS) analysis indicated that metacinnabar (β-HgS) was the main mercury species in a marine sediment, whereas organic Hg-thiol (Hg(SR) 2 ) was the main mercury species in a terrestrial sediment. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis of the marine sediment suggests that half of the Hg in the <0.5 μm size fraction existed as individual nanoparticles, which were β-HgS based on XAS analyses. Glutathione-extractable mercury was higher for samples containing Hg(SR) 2 species than β-HgS species and correlated well with the amount of Hg biomethylation. This particle-scale understanding of how Hg speciation and particle size affect mercury bioavailability potential helps explain the heterogeneity in Hg methylation in natural sediments.

Technologies for removal of mercury from produced water and hydrocarbon phases are desired by oil and gas production facilities, oil refineries, and petrochemical plants. Herein, we synthesize and demonstrate the efficacy of an amphiphilic, thiol-abundant (11.8 wt % S, as thiol) polymer nanogel that can remove environmentally relevant mercury species from both produced water and the liquid hydrocarbon. The nanogel disperses in both aqueous and hydrocarbon phases. It has a high sorption affinity for dissolved Hg(II) complexes and Hg-dissolved organic matter complexes found in produced water and elemental (Hg 0 ) and soluble Hg-alkyl thiol species found in hydrocarbons. X-ray absorption spectroscopy analysis indicates that the sorbed mercury is transformed to a surface-bound Hg(SR) 2 species in both water and hydrocarbon regardless of its initial speciation. The nanogel had high affinity to native mercury species present in real produced water (>99.5% removal) and in natural gas condensate (>85% removal) samples, removing majority of the mercury species using only a 50 mg L -1 applied dose. This thiolated amphiphilic polymeric nanogel has significant potential to remove environmentally relevant mercury species from both water and hydrocarbon at low applied doses, outperforming reported sorbents like sulfur-impregnated activated carbons because of the mass of accessible thiol groups in the nanogel.

The objective of this study is to assess how method parameters impact the extraction of moderately soluble CuO nanoparticles (NPs) from a standard natural soil (LUFA 2.1) suitable for chemical analysis. The extraction procedure is comprised of three steps: (i) preconditioning the soil to increase the sodium adsorption ratio, (ii) extracting colloids/NPs from the soil matrix using sonication and a dispersing agent, and (iii) separating the dissolved and nanoparticulate CuO fractions using cloud point extraction. Method parameters of the extraction procedure, including sonication, number of extraction cycles, and dispersing agent, were adjusted to achieve the highest extraction of CuO NPs, while minimizing dissolution. The maximum recovery of CuO NPs ranged from 31% to 42% for an amended concentration range of 10-250 mg-Cu (kg soil) -1 using a preconditioning step to exchange divalent cations for monovalent ions, 0.2% carboxymethyl cellulose (CMC) 700 kg mol -1 as the dispersing agent, probe sonication for 1 min, 3 extraction cycles, and a 1:10 soil-to-liquid ratio. CuO NPs that are polyvinylpyrrolidone (PVP)-coated with a greater stability against aggregation had significantly higher extractability and dissolution. This procedure is the first to effectively extract moderately soluble NPs from soil and experimentally separate them from their dissolved fraction and can be applied to other moderately soluble metal containing natural, incidental, or engineered NPs in soil.

The application of nanoparticles (NPs) to soils, as either fertilizers or fungicides (e.g., CuO NPs), has been proposed to improve the sustainability of agriculture. The observed effects could result directly from the NP-plant interactions or indirectly through effects on the soil microbiome. The objective of this study was to assess the effects of CuO NPs on the changes in the bacterial community structure and nitrogen-cycling-associated functions in a high pH soil and to correlate these changes with nitrate accumulation, soil parameter changes, and plant growth over 28 days. Triticum aestivum seedlings were exposed to 50 mg/kg CuO NPs, 50 mg/kg CuSO 4 , or 0.5 mg/kg CuSO 4 in a standard soil (Lufa 2.1 soil, pH adjusted to 7.6). While Cu treatments reduced nitrate accumulation in the bulk soil, the effects were opposite in the rhizosphere (the soil influenced by root exudates). While nitrate accumulation in bulk soil negatively correlated with total Cu concentration, part of the nitrate concentration in the rhizosphere was explained by root uptake during plant growth, the rest being modulated by Cu treatments. The abundance of genes involved in the nitrogen cycle in the rhizosphere soil correlated with the ionic copper concentration. The increased nitrate concentration in the rhizosphere correlated with an increase of the gene abundance related to the nitrogen fixation and a decrease of denitrification gene abundance. Microbial diversity in bulk or rhizosphere soil under the different treatments alone could not explain these variations, while differences in the assemblages of bacteria associated with these functional gene abundances gave good insights. This study highlights the complexity of microbial N-related function in the rhizosphere and the need to characterize the rhizosphere soil, plant growth and root activity, NP (bio)transformations, along with microbial networks, to understand the impact of agrochemicals (here CuO NPs) on soil fertility.