Speciation and fate of toxic cadmium in contaminated paddy soils and rice using XANES/EXAFS spectroscopy

Protaetia brevitarsis larvae produce frass that can be used as an additive to immobilize Cd and improve fertility in alkaline soils

Bioconversion of agricultural waste by Protaetia brevitarsis larvae (PBL) holds significant promise for producing high-quality frass organic amendments. However, the effects and mechanisms of PBL frass on Cd immobilization in an alkaline environment remain poorly understood. In this study, three types of frass, namely maize straw frass (MF), rice straw frass (RF), and sawdust frass (SF), were produced by feeding PBL. The Cd immobilization efficiencies of three frass in alkaline solutions and soils were investigated through batch sorption and incubation experiments, and spectroscopic techniques were employed to elucidate the sorption mechanisms of Cd onto different frass at the molecular level. The results showed that MF proved to be an efficient sorbent for Cd in alkaline solutions (176.67-227.27 mg g-1). X-ray absorption near-edge structure (XANES) spectroscopy indicated that Cd immobilization in frass is primarily attributed to the association with organic matter (OM-Cd, 78-90%). And MF had more oxygen-containing functional groups than the other frass. In weakly alkaline soils, MF application (0.5-1.5%) significantly decreased Cd bioavailability (5.65-18.48%) and concurrently improved soil nutrients (2.21-56.79%). Redundancy analysis (RDA) unveiled that pH, CEC, and available P were important factors controlling Cd fractions. Path analysis demonstrated that MF application affected Cd bioavailability directly and indirectly by influencing soil chemical properties and nutrients. In summary, MF, the product of PBL-mediated conversion maize straw, demonstrated promise as an effective organic amendment for Cd immobilization and fertility improvement in alkaline soils.

Immobilization mechanisms of Sr(II), Ni(II), and Cd(II) on glomalin-related soil protein in mangrove sediments at the microscopic scale

Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of -OH and -COOH groups with the metal. The -COOH and -OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of -COOH groups followed by -OH groups. The presence of the Ni-C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr-C and Cd-C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration.

The determination of thallium in the environment: A review of conventional and advanced techniques and applications

Thallium (Tl) is a potential toxicity element that poses significant ecological and environmental risks. Recently, a substantial amount of Tl has been released into the environment through natural and human activities, which attracts increasing attention. The determination of this hazardous and trace element is crucial for controlling its pollution. This article summarizes the advancement and progress in optimizing Tl detection techniques, including atomic absorption spectroscopy (AAS), voltammetry, inductively coupled plasma (ICP)-based methods, spectrophotometry, and X-ray-based methods. Additionally, it introduces sampling and pretreatment methods such as diffusive gradients in thin films (DGT), liquid-liquid extraction, solid phase extraction, and cloud point extraction. Among these techniques, ICP-mass spectrometry (MS) is the preferred choice for Tl detection due to its high precision in determining Tl as well as its species and isotopic composition. Meanwhile, some new materials and agents are employed in detection. The application of novel work electrode materials and chromogenic agents is discussed. Emphasis is placed on reducing solvent consumption and utilizing pretreatment techniques such as ultrasound-assisted processes and functionalized magnetic particles. Most detection is performed in aqueous matrices, while X-ray-based methods applied to solid phases are summarized which provide non-destructive analysis. This work improves the understanding of Tl determination technology while serving as a valuable resource for researchers seeking appropriate analytical techniques.

Exposure risks of lead and other metals to humans: A consideration of specific size fraction and methodology

Particle size is a critical influencing factor in assessing human exposure risk as fine particles are generally more hazardous than larger coarse particles. However, how particle composition influences human health risk is only poorly understood as different studies have different utilised different definitions and as a consequence there is no consensus. Here, with a new methodology taking insights of each size fraction load (%GSFload), metal bioaccessibility, we classify which specific particle size can reliably estimate the human exposure risk of lead and other metals. We then validate these by correlating the metals in each size fraction with those in human blood, hair, crop grain and different anthropogenic sources. Although increasing health risks are linked to metal concentration these increase as particle size decrease, the adjusted-risk for each size fraction differs when %GSFload is introduced to the risk assessment program. When using a single size fraction (250-50 µm, 50-5 µm, 5-1 µm, and < 1 µm) for comparison, the risk may be either over- or under-estimated. However, by considering bulk and adjusting the risk, it would be possible to obtain results that are closer to the real scenarios, which have been validated through human responses and evidence from crops. Fine particle size fractions (< 5 µm) bearing the mineral crystalline or aggregates (CaCO3, Fe3O4, Fe2O3, CaHPO4, Pb5(PO4)3Cl) alter the accumulation, chemical speciation, and fate of metals in soil/dust/sediment from the different sources. Loaded lead in the size fraction of < 50 µm has a significantly higher positive association with the risk-receptor biomarkers (BLLs, Hair Pb, Corn Pb, and Crop Pb) than other size fractions (bulk and 50-250 µm). Thus, we conclude that the < 50 µm fraction would be likely to be recommended as a reliable fraction to include in a risk assessment program. This methodology acts as a valuable instrument for future research undertakings, highlighting the importance of choosing suitable size fractions and attaining improved accuracy in risk assessment results that can be effectively compared.

Synthesis and properties of nano-cadmium oxide and its size-dependent responses by barley plant

Present study included technological methods that made it possible to synthesize CdO nanoparticles and carry out their qualitative and quantitative diagnostics, confirming the as-prepared CdO nanoparticles (NPs) were spherical and had a size of 25 nm. Then, under the conditions of the model experiment the effect of CdO in macro and nanosized particles on absorption, transformation, and structural and functional changes occurring in cells and tissues of Hordeum vulgare L. (spring barley) during its ontogenesis was analyzed. Different analytical techniques were used to detect the transformation of CdO forms: Fourier-transform infrared spectroscopy (FTIR), Dynamic light scattering (DLS), X-ray fluorescence analysis (XRF), Scanning electron microscopy (SEM-EDXMA and TEM), X-ray diffraction (XRD), and X-ray absorption fine structure, consists of XANES - X-ray absorption near edge structure, and EXAFS - Extended X-ray absorption fine structure. Quantitative differences in the elemental chemical composition of barley root and leaf samples were observed. The predominant root uptake of Cd was revealed. CdO-NPs were found to penetrate deeply into barley plant tissues, where they accumulated and formed new mineral phases such as Cd5(PO4)3Cl and CdSO4 according to XRD analysis. The molecular-structural state of the local Cd environment in plant samples corresponding to Cd-O and Cd-Cd. The toxicity of CdO-NPs was found to significantly affect the morphology of intracellular structures are the main organelles of photosynthesis therefore, destructive changes in them obviously reduce the level of metabolic processes ensuring the growth of plants. This study is an attempt to show results how it is possible to combine some instrumental techniques to characterize and behavior of NPs in complex matrices of living organisms.

Pb speciation and elemental distribution in leeks by micro X-ray fluorescence and X-ray absorption near-edge structure

Vegetables are crucial to a human diet as they supply the body with essential vitamins, minerals, etc. Heavy metals that accumulate in plants consequently enter the food chain and endanger people's health. Studying the spatial distribution and chemical forms of elements in plant/vegetable tissues is vital to comprehending the potential interactions between elements and detoxification mechanisms. In this study, leek plants and soil from vegetable gardens near lead-zinc mines were collected and cultivated with 500 mg L-1 PbNO3 solutions for three weeks. Micro X-ray fluorescence was used to map the distribution of Pb and other chemical elements in leek roots, and X-ray absorption near-edge spectroscopy was used to assess the Pb speciation in leek roots and leaves. These findings demonstrated that Pb, Cu, Mn, Cr, Ti and Fe were detected in the outer rings of the root's cross section, and high-intensity points were observed in the epidermis. Zn, K and Ca, on the other hand, were distributed throughout the root's cross section. Leek root and leaf contained significant quantities of lead phosphate and basic lead carbonate at more than 80%, followed by lead sulfide (19%) and lead stearate (11.1%). The capacity of leek roots to convert ambient lead into precipitated lead and fix it on the root epidermis and other inner surfaces is a key mechanism for reducing the toxic effects of Pb.

Changes in the concentration, distribution, and speciation of arsenic in the hyperaccumulator Pteris vittata at different growth stages

The arsenic (As) hyperaccumulator has become a model plant for the study of the interaction between plants and trace elements. However, the change in As concentration, distribution and speciation of hyperaccumulator Pteris vittata at different growth stages, especially with the aging process remains unknown. We collected P. vittata at different growth ages and analyzed As concentration, distribution, and speciation. Furthermore, metabolic profiling was conducted for P. vittata at different growth stages. With aging, the reduced glutathione/ oxidized glutathione ratio decreased while the malondialdehyde content increased, accompanied by the change in the main As speciation in P. vittata from arsenite to arsenate. Metabolic profiling also indicated significant difference in the compositions of metabolites during different growth stages. Specifically, flavonoid compounds were found to be positively correlated with As concentration. Results indicated that with the aging of P. vittata, the redox potential increased in the pinnae, leading to the oxidation of As, which may have impacted the distribution of As in this fern. Furthermore, the correlation between As concentration and flavonoid compounds implied the essential role of flavonoid metabolism in the accumulation and transport of As in this plant.

Speciation of heavy metals in soils and their immobilization at micro-scale interfaces among diverse soil components

Heavy metal (HM) pollution of soils is a globally important ecological and environmental problem. Previous studies have focused on i) tracking pollution sources in HM-contaminated soils, ii) exploring the adsorption capacity and distribution of HMs, and iii) assessing phyto-uptake of HMs and their ecotoxicity. However, few reviews have systematically summarized HM pollution in soil-plant systems over the past decade. Understanding the mechanisms of interaction between HMs and solid soil components is consequently key to effectively controlling and remediating HM pollution. However, the compositions of solid soil phases are diverse, their structures are complex, and their spatial arrangements are heterogeneous, all leading to the formation of soil micro-domains that exhibit different particle sizes and surface properties. The various soil components and their interactions ultimately control the speciation, transformation, and bioavailability of HMs in soils. Over the past few decades, the extensive application of advanced instrumental techniques and methods has greatly expanded our understanding of the behavior of HMs in organic mineral assemblages. In this review, studies investigating the immobilization of HMs by minerals, organic compounds, microorganisms, and their associated complexes are summarized, with a particular emphasis on the interfacial adsorption and immobilization of HMs. In addition, methods for analyzing the speciation and distribution of HMs in aggregates of natural soils with different particle sizes are also discussed. Moreover, we also review the methods for speciating HMs at mineral-organic micro-scale interfaces. Lastly, developmental prospects for HM research at inorganic-organic interfaces are outlined. In future research, the most advanced methods should be used to characterize the interfaces and in situ characteristics of metals and metal complexes. In particular, the roles and contributions of microorganisms in the immobilization of HMs at complex mineral-organic interfaces require significant further investigation.

Transformation and fate of thallium and accompanying metal(loid)s in paddy soils and rice: A case study from a large-scale industrial area in China

Thallium (Tl) is an extremely toxic metal, while its occurrence and fate in paddy soil environment remain understudied. Herein, the enrichment and migration mechanisms and potential health risks of Tl and metal(loid)s were evaluated in paddy soils surrounding an industrial park utilizing Tl-bearing minerals. The results showed that Tl contamination was evident (0.63-3.16 mg/kg) in the paddy soils and Tl was generally enriched in root of rice (Oryza sativa L.) with a mean content of 1.27 mg/kg. A remarkably high level of Tl(III) (30-50%) was observed in the paddy soils. Further analyses by STEM-EDS and XPS indicated that Tl(I) in the paddy soils was jointly controlled by adsorption, oxidation, and precipitation of Fe/Mn(hydr)oxide (e.g. hematite and birnessite), which might act as important stabilization mechanisms for inhibiting potential Tl uptake by rice grains. The health quotient (HQ) values indicated a potentially high Tl risk for inhabitants via consumption of the rice grains. Therefore, it is critical to establish effective measures for controlling the discharge of Tl-containing waste and wastewater from different industrial activities to ensure food safety in the rice paddy soils.

Stabilization of cadmium in contaminated sediment based on a nanoremediation strategy: Environmental impacts and mechanisms

Nanomaterials have great application potential for the remediation of heavy metal contaminated sediments, but their environmental impacts are still limited. Herein, graphene oxide-supported nanoscale zero-valent iron (GNZVI) was synthesized to explore its role in mediating the immobilization of cadmium (Cd) from contaminated river sediments, with the consideration of the potential impacts on sediment enzyme activities and bacterial community. Compared to NZVI and GO, GNZVI could more effectively promote the transformation of mobile Cd into stable speciation with a maximum residual percentage increasing by 64.82% after 56 days of treatment. The activities of urease, catalase and sucrase were gradually increased and stabilized with the prolongation of treatment time, indicating that the metabolic function of sediments was recovered. 16 S rRNA gene sequencing results confirmed that the application of GNZVI increased the abundance of some Fe(III)-reducing bacteria, further stimulating the bioavailability of organic matter. Additionally, the properties of GO were gradually changed via microbial reduction and finally showed similar properties to rGO. The critical role of rGO as an electrical conductor was to promote the electron transfer process of microbial Fe(III) mineral reduction, which redistributes part of the Fe(III) mineral-associated Cd to more stable secondary iron minerals, thereby further improving the stabilization efficiency of r-GNZVI for Cd.

Mechanism of Pb absorption in wheat grains

Atmospheric deposition is the primary source of external environmental media for lead (Pb) influx in wheat grains. However, the mechanisms of Pb grain absorption remains unclear. We explored this mechanism through comparative experiments, involving defoliating leaf blades (TG) and a control group (CK) of field wheat after the anthesis stage. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis displayed that leaves and ears can directly absorb atmospheric deposition Pb through stomata. Compared with CK, the yield, grain Pb content, and grain Pb accumulation of TG wheat were significantly decreased by 13.25%, 22.10%, and 32.58%, respectively. Combined with the Pb isotope analysis, the ear had the highest contribution to grain Pb followed by leaf and root. Simultaneously, the absorption rate of grain Pb demonstrated a dynamic trend of "N" shape. Dominant contribution periods of the root, leaf, and ear organs to grain Pb accumulation were different. Unlike the root system, the contribution of the aboveground to grain Pb increased gradually, and the contribution of leaf and ear to grain Pb were mainly concentrated in the early and late filling stage, respectively. Our findings can provide a theoretical basis for the control of Pb pollution in grains.