X-ray fluorescence spectroscopy (XRF) for metallome analysis of herbarium specimens

Fast, in situ, and eco-friendly determination of Mn in plant leaves using portable X-ray fluorescence spectrometry for agricultural and environmental applications

The portable X-ray fluorescence (pXRF) spectrometry has been very useful for the characterization of different earth materials, and its application for foliar analysis is really promising. The performance of pXRF for foliar analysis depends on several factors such as concentration of the elements, fluorescence yield which is influenced by atomic number, spectral interference, and water content. Mn is one of the elements that present a prominent fluorescence peak. In this sense, it was hypothesized that pXRF can directly determine the Mn concentration on foliar samples, even when used on intact leaves (fresh or dry) being a useful tool for agronomic and environmental purposes. Thus, the objective was to assess the performance of a pXRF to determine Mn concentration in two different foliar datasets from Brazil/South America and Mali/Africa. In the Brazilian dataset, leaves from eight crops (common bean, castor plant, coffee, eucalyptus, guava tree, maize, mango, and soybean) were scanned via pXRF at the following conditions: intact and fresh leaves, intact and dry leaves, and powdered samples). In the Malian dataset, powdered samples from cotton and maize were analyzed via pXRF. For comparison, Mn concentration was also determined after nitro-perchloric digestion followed by quantification via inductively coupled plasma optical emission spectroscopy (ICP-OES). After descriptive statistics, linear regressions were performed for all sample preparation conditions in both datasets, using Mn concentrations obtained through pXRF and the acid digestion method. The data quality level of all linear regressions was considered quantitative with high R (0.93 to 0.98) and R2 (0.87 to 0.96) values. The direct analysis of Mn via pXRF on intact and fresh leaves yielded R of 0.93, R2 of 0.87, and a low relative standard deviation (< 10%). The manufactured pXRF calibration used in this work allowed an accurate direct Mn determination in plant leaves. Considering the importance of Mn as a plant micronutrient and its potential toxicity depending on soil redox conditions, the fast, in situ, non-destructive, and eco-friendly determination via pXRF has a tremendous agronomic and environmental application worldwide.

The Plant Ionome as a Functional Trait: Variation across Bioclimatic Regions and Functional Groups

Plant chemical composition is a trait gaining increasing importance in plant ecology. However, there is limited research on the patterns and drivers of its variation among different plant functional groups and bioclimatic regions. We conducted an analysis of ionomes utilising X-ray fluorescence on 83 plant species from four distinct functional groups (grasses, legumes, forbs and woody species); we marked plots across 15 sites located in both the desert and Mediterranean bioclimatic regions. The primary factors influencing variations in ionomes are predominantly attributed to bioclimatic factors rather than soil composition. Across all functional groups, plants from the Mediterranean region are characterised by greater association with calcium, whereas desert plants exhibit a higher affinity for strontium (Sr), suggesting its potential role in drought tolerance. Among functional groups, grasses uniquely exhibit distinct ionomic features, primarily due to their higher silicon (Si) concentrations. Plant species' affinities for certain elements and their interactions are likely driven by physiological constraints, whereas variations within a functional group are mostly driven by environmental conditions. We conclude that interactions among elements form physiological phenotypes shaped by natural selection under large-scale environmental variability, making plant ionome composition an important plant functional trait.

The use of a portable X-ray fluorescence spectrometer for measuring nickel in plants: sample preparation and validation

X-ray fluorescence is a fast, cost-effective, and eco-friendly method for elemental analyses. Portable X-ray fluorescence spectrometers (pXRF) have proven instrumental in detecting metals across diverse matrices, including plants. However, sample preparation and measurement procedures need to be standardized for each instrument. This study examined sample preparation methods and predictive capabilities for nickel (Ni) concentrations in various plants using pXRF, employing empirical calibration based on inductively coupled plasma optical emission spectroscopy (ICP-OES) Ni data. The evaluation involved 300 plant samples of 14 species with variable of Ni accumulation. Various dwell times (30, 60, 90, 120, 300 s) and sample masses (0.5, 1.0, 1.5, 2.0 g) were tested. Calibration models were developed through empirical and correction factor approaches. The results showed that the use of 1.0 g of sample (0.14 g cm-2) and a dwell time of 60 s for the study conditions were appropriate for detection by pXRF. Ni concentrations determined by ICP-OES were highly correlated (R2 = 0.94) with those measured by the pXRF instrument. Therefore, pXRF can provide reliable detection of Ni in plant samples, avoiding the digestion of samples and reducing the decision-making time in environmental management.

Prospecting for rare earth element (hyper)accumulators in the Paris Herbarium using X-ray fluorescence spectroscopy reveals new distributional and taxon discoveries

BACKGROUND

Rare earth elements (REEs) are increasingly crucial for modern technologies. Plants could be used as a biogeochemical pathfinder and a tool to extract REEs from deposits. However, a paucity of information on suitable plants for these tasks exists.

METHODS

We aimed to discover new REE-(hyper)accumulating plant species by performing an X-ray fluorescence (XRF) survey at the Herbarium of the Muséum national d'Histoire naturelle (MNHN, Paris, France). We selected specific families based on the likelihood of containing REE-hyperaccumulating species, using known taxa that accumulate REEs. A total of 4425 specimens, taken in the two main evolutionary lineages of extant vascular plants, were analysed, including the two fern families Blechnaceae (n = 561) and Gleicheniaceae (n = 1310), and the two flowering plant families Phytolaccaceae (n = 1137) and Juglandaceae (n = 1417).

KEY RESULTS

Yttrium (Y) was used as a proxy for REEs for methodological reasons, and a total of 268 specimens belonging to the genera Blechnopsis (n = 149), Dicranopteris (n = 75), Gleichenella (n = 32), Phytolacca (n = 6), Carya (n = 4), Juglans (n = 1) and Sticherus (n = 1) were identified with Y concentrations ranging from the limit of detection (LOD) >49 µg g-1 up to 1424 µg g-1. Subsequently, analysis of fragments of selected specimens by inductively coupled plasma atomic emission spectroscopy (ICP-AES) revealed that this translated to up to 6423 µg total REEs g-1 in Dicranopteris linearis and up to 4278 µg total REEs g-1 in Blechnopsis orientalis which are among the highest values ever recorded for REE hyperaccumulation in plants. It also proved the validity of Y as an indicator for REEs in XRF analysis of herbarium specimens. The presence of manganese (Mn) and zinc (Zn) was also studied by XRF in the selected specimens. Mn was detected in 1440 specimens ranging from the detection limit at 116 µg g-1 up to 3807 µg g-1 whilst Zn was detected in 345 specimens ranging from the detection limit at 77 µg g-1 up to 938 µg g-1.

CONCLUSIONS AND IMPLICATIONS

This study led to the discovery of REE accumulation in a range of plant species, substantially higher concentrations in species known to be REE hyperaccumulators, and records of REE hyperaccumulators outside of the well-studied populations in China.

High Recovery of Ceramic Membrane Cleaning Remediation by Ozone Nanobubble Technology

The persistent issue of ceramic membrane fouling poses significant challenges to its widespread implementation. To address this concern, ozone nanobubbles (ozone-NBs) have garnered attention due to their remarkable mass transfer efficiency. In this investigation, we present a novel ozone-NB generator system to effectively clean a fouled ceramic membrane that is typically employed in the dye industry. The surface characteristics of the ceramic membrane underwent significant alterations, manifesting incremental changes in surface roughness and foulant accumulation reduction, as evidenced in atomic force microscopy, scanning electron microscopy, X-ray fluorescence, and energy-dispersive spectroscopy. Remarkably, the sequential 4 h cleaning process demonstrates an effective outcome leading to an almost 2-fold enhancement in the membrane flux. The initial fouled state of 608 L/h/m2 increased to 1050 L/h/m2 in the 4 h state with a recovery of 50%. We propose such membrane performance improvement governed by the ozone-NBs with a size distribution of 213.2 nm and a zeta potential value of -20.26 ± 0.13 mV, respectively. This effort showcases a substantial innovative and sustainable technology approach toward proficient foulant removal in water treatment applications.

Thallium hyperaccumulation status of the violets of the Allchar arsenic-thallium deposit (North Macedonia) confirmed through synchrotron µXRF imaging

The abandoned Allchar Mine in the Republic of North Macedonia is a globally unique deposit with the highest known grades of thallium (Tl) and arsenic (As) mineralization. We aimed to determine the distribution of As and Tl in whole dehydrated shoots of the three Viola taxa using synchrotron micro-X-ray fluorescence analysis. Additionally, soil and plant organ samples were collected from all three Viola taxa at the Allchar site and analysed using inductively coupled plasma-atomic emission spectrometry. Concentrations of Tl were extremely high in all three Viola taxa (up to 58 900 mg kg-1), but concentrations of As were highly variable with V. tricolor subsp. macedonica and V. allchariensis having low As (up to 20.2 and 26.3 mg kg-1, respectively) and V. arsenica having the highest concentrations (up to 381 mg kg-1). The extremely high Tl in all three species is endogenous and not a result of contamination. Arsenic in V. tricolor subsp. macedonica and V. allcharensis is strongly affected by contamination, but not in V. arsenica where it appears to be endogenous. The pattern of As enrichment in V. arsenica is very unusual and coincides with Ca-oxalate deposits and Br hotspots. The results of this study could form the basis for more detailed investigations under controlled conditions, including plant dosing experiments.

Reflectance spectroscopy as a promising tool for 'sensing' metals in hyperaccumulator plants

MAIN CONCLUSION

The VNIR reflectance spectra of nickel hyperaccumulator plant leaves have spectral variations due to high nickel concentrations and this property could potentially be used for discovery of these plants.  Hyperaccumulator plants accumulate high concentrations of certain metals, including manganese, cobalt, or nickel. Of these metals, the divalent ions of nickel have three absorption bands in the visible to near-infrared region which may cause variations in the spectral reflectance of nickel hyperaccumulator plant leaves, but this has not been investigated previously. In this shortproof-of-concept study, the spectral reflectance of eight different nickel hyperaccumulator plant species leaves were subjected to visible and near-infrared and shortwave infrared (VNIR-SWIR) reflectance spectrum measurements in dehydrated state, and for one species, it was also assessed in hydrated state. Nickel concentrations in the plant leaves were determined with other methods and then correlated to the spectral reflectance data. Spectral variations centred at 1000 ± 150 nm were observed and had R-values varying from 0.46 to 0.96 with nickel concentrations. The extremely high nickel concentrations in nickel hyperaccumulator leaves reshape their spectral reflectance features, and the electronic transition of nickel-ions directly contributes to absorption at ~ 1000 nm. Given that spectral variations are correlated with nickel concentrations it make VNIR-SWIR reflectance spectrometry a potential promising technique for discovery of hyperaccumulator plants, not only in the laboratory or herbarium, but also in the field using drone-based platforms. This is a preliminary study which we hope will instigate further detailed research on this topic to validate the findings and to explore possible applications.

Assessing metal ion transporting activity of ZIPs: Intracellular zinc and iron detection

Zrt/Irt-like proteins (ZIPs or SLC39A) are a large family of metal ion transporters mainly responsible for zinc uptake. Some ZIPs have been shown to specifically transport zinc, whereas others have broader substrate specificity in divalent metal ion trafficking, notably those of zinc and iron ions. Measuring intracellular zinc and iron levels helps assess their molecular and physiological activities. This chapter presents step-by-step methods for evaluating intracellular metal ion concentrations, including direct measurement using inductively coupled plasma-mass spectrometry (ICP-MS), chemical staining, fluorescent probes, and indirect reporter assays such as activity analysis of enzymes whose activities are dependent on metal ion availability.