High Molybdenum availability for evolution in a Mesoproterozoic lacustrine environment

Probing atomic-scale processes at the ferrihydrite-water interface with reactive molecular dynamics

Interfacial processes involving metal (oxyhydr)oxide phases are important for the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. Consequently, these processes influence ecosystem health and functioning, and have shaped the biological and environmental co-evolution of Earth over geologic time. Here we employ reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy to study the molecular-scale interfacial processes that influence surface complexation in ferrihydrite-water systems containing aqueousMoO 4 2 - . We validate the utility of this approach by calculating surface complexation models directly from simulations. The reactive force-field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. We find that upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. We observed how this restructuring leads to a different interfacial hydrogen bond network compared to bulk water by monitoring water dynamics. Using umbrella sampling, we constructed the free energy landscape of aqueousMoO 4 2 - adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with the values reported by experimental surface complexation models. These findings are important as reactive molecular dynamics opens new avenues to study mineral-water interfaces, enriching and refining surface complexation models beyond their foundational assumptions.

Ultrahigh-resolution imaging of biogenic phosphorus and molybdenum in palaeoproterozoic gunflint microfossils

Phosphorus and molybdenum play important roles in the formation of microbial cell structures and specific enzymes crucial for metabolic processes. Nevertheless, questions remain about the preservation of these elements within ancient microfossils. Here, we present shape-accurate ion images capturing phosphorus and molybdenum on Palaeoproterozoic filamentous microfossils by pioneering a methodology using lateral high-resolution secondary ion mass spectrometry. Introducing electrically conductive glass for mounting isolated microfossils facilitated clearer observations with increased secondary ion yields. Phosphorus was detected along the contours of microfossils, providing direct evidence of phospholipid utilization in the cell membrane. Trace amounts of molybdenum were detected within microfossil bodies, suggesting potential remnants of molybdenum-bearing proteins, such as nitrogenase. These findings align with the hypothesized cyanobacterial origin of filamentous gunflint microfossils. Our methodology introduces a groundbreaking tool for obtaining crucial insights into the cellular evolution and metabolic pathways of microorganisms, allowing comparisons of their morphological characteristics.

Identification of factors driving the spatial distribution of molybdenum (Mo) in topsoil in the Longitudinal Range-Gorge Region of Southwestern China using the Geodetector model

As a key component of plant nitrogen-fixing enzymes and a variety of human coenzyme factors, molybdenum (Mo) plays an essential role in supporting both plant growth and human health. Soil is a key medium for the cycling of Mo in the biosphere. However, the driving anthropogenic and natural factors governing the spatial distribution of Mo in soil and their interactions are not well understood. To determine the factors that affect the spatial patterns of Mo in topsoil, 6980 samples were collected from the Longitudinal Range-Gorge Region (Linshui County, Sichuan Province, China). In this area, tall mountains are adjacent to deep valleys. Topsoil with enriched Mo is mostly distributed in mountainous areas. The most important factors influencing Mo in topsoil are soil parent materials (q = 0.482), altitude (q = 0.256), and soil type (q = 0.259). There are synergistic effects among the various driving factors [q(X1 ∩ X2) > Max[q(X1), q(X2)]]. The Geodetector model was used to validate the magnitude of the interaction effects. The contribution to interacting factors is nonlinearly enhanced when the contribution of a single factor was low (any two factors of aspect, road distance, land use type, and S). The contribution to interacting factors is enhanced bidirectionally when the contribution of a single factor was high (any two factors of altitude, soil type, soil parent material, OM, and TFe2O3). When the contribution of one factor is high and the other is low, the contributing to interacting factors is mostly enhanced bidirectionally and a few are nonlinearly enhanced.

Geochemical elements in suspended particulate matter of Ensenada de La Paz Lagoon, Baja California Peninsula, Mexico: Sources, distribution, mass balance and ecotoxicological risks

The present study aimed to evaluate multi-element concentrations (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr) in suspended particulate material (SPM) collected from Ensenada de La Paz (ELP) lagoon, Baja California Sur, Mexico in two different periods (September and May) to comprehend their origin, geochemical behavior, mass transfer and associated ecotoxicological risks. The 24 hr variation coefficient of volumetric SPM levels were found to be 51.7% in September and 40.5% in May, signifying the effects of oceanic waters. The calculated enrichment factor (EF) values for all the studied elements were of higher magnitude because of the high surface area and oxide nature of SPM, and in this study, Mo had the highest EF of 46.77 probably due to its origin from continental weathering. From the ecotoxicological perspective, the integrated toxic risk index revealed low toxic risk to the benthic community. However, the mean-ERM-Quotient calculated using the particulate concentrations of As, Cd, Cr, Cu, Ni, Pb indicated 9% probability of toxicity to biota. The comprehensive geochemical and ecotoxicological assessment of particulate metal concentrations in the ELP lagoon signify low to moderate contamination.

Enrichment mechanisms of Mo in soil in the karst region Guangxi, China

Soils developed in karst regions have naturally high background values of molybdenum (Mo) due to geological factors. However, the enrichment mechanism of Mo in these soils are not fully understood, making it challenging to assess their ecological risk and utilize Mo-rich land resources. To shed light on this issue, this study collected and analyzed data from the 1:50,000 geochemical survey in Guangxi, including 536,503 sets of soil data and 3043 sets of rock data, as well as 40 sets of carbonate rock-soil from typical karst regions. The results showed that soil Mo enrichment is highly correlated with the distribution of carbonate rocks in karst regions. The carbonate rocks in these regions contain Mo ranging from 0.03 to 1.06 mg·kg^-1 (with a mean of 0.22 mg·kg^-1). In comparison, the soil Mo derived from carbonate rocks can reach up to 6.00 mg·kg^-1 (with a mean of 2.75 mg·kg^-1), representing an average enrichment of soil Mo that is 24 times higher compared to the carbonate parent rock. The enrichment of soil Mo in karst regions is primarily controlled by secondary enrichment during the weathering process of carbonate. During the insoluble residue accumulation process, the dissolution of carbonate leads to a dramatic reduction in bedrock volume, and the adsorption of clay minerals and Fe minerals in insoluble residues plays an essential role in Mo enrichment during these stages. During the soil-forming stage of the insoluble residue, most Mo leaches into the water body due to the mineral transformation of insoluble residue. Consequently, as Fe-Mn nodules in soils become more enriched with increasing weathering intensity, some Mo is absorbed and passivated by iron and manganese oxides (hydroxides). Accordingly, the contribution of Fe-Mn nodules and the degree of leaching were closely related to the enrichment of soil Mo in karst regions. This study provides insights into the enrichment mechanisms of Mo in soils developed in karst regions, which will help to evaluate their ecological risk in these environments.

Mesoproterozoic surface oxygenation accompanied major sedimentary manganese deposition at 1.4 and 1.1 Ga

Manganese (Mn) oxidation in marine environments requires oxygen (O₂ ) or other reactive oxygen species in the water column, and widespread Mn oxide deposition in ancient sedimentary rocks has long been used as a proxy for oxidation. The oxygenation of Earth's atmosphere and oceans across the Archean-Proterozoic boundary are associated with massive Mn deposits, whereas the interval from 1.8-1.0 Ga is generally believed to be a time of low atmospheric oxygen with an apparent hiatus in sedimentary Mn deposition. Here, we report geochemical and mineralogical analyses from 1.1 Ga manganiferous marine-shelf siltstones from the Bangemall Supergroup, Western Australia, which underlie recently discovered economically significant manganese deposits. Layers bearing Mn carbonate microspheres, comparable with major global Mn deposits, reveal that intense periods of sedimentary Mn deposition occurred in the late Mesoproterozoic. Iron geochemical data suggest anoxic-ferruginous seafloor conditions at the onset of Mn deposition, followed by oxic conditions in the water column as Mn deposition persisted and eventually ceased. These data imply there was spatially widespread surface oxygenation ~1.1 Ga with sufficiently oxic conditions in shelf environments to oxidize marine Mn(II). Comparable large stratiform Mn carbonate deposits also occur in ~1.4 Ga marine siltstones hosted in underlying sedimentary units. These deposits are greater or at least commensurate in scale (tonnage) to those that followed the major oxygenation transitions from the Neoproterozoic. Such a period of sedimentary manganogenesis is inconsistent with a model of persistently low O₂ throughout the entirety of the Mesoproterozoic and provides robust evidence for dynamic redox changes in the mid to late Mesoproterozoic.

Molybdenum Release Triggered by Dolomite Dissolution: Experimental Evidence and Conceptual Model

The injection of oxygenated water into anoxic aquifers during managed aquifer recharge (MAR) can cause the mobilization of metal(loid)s. Here, we study the processes controlling MAR-induced molybdenum (Mo) release in dolomitic aquifers. Sequential chemical extractions and energy dispersive X-ray spectroscopy combined with scanning electron microscopy point to an association of Mo with easily soluble sulfurized organic matter present in intercrystalline spaces of dolomites or directly incorporated within dolomite crystals. The easily soluble character was confirmed by a batch experiment that demonstrated the rapid mobilization of Mo, dissolved organic carbon, and sulfur. The type and time of batch solution contact with the sulfurized organic matter impacted the release of Mo, as demonstrated by a 36% increase in Mo concentrations when shaking was intensified. Based on the experimental results, a conceptual model for the release of Mo was formulated, where (i) the injection of oxygenated water causes the oxidation of pyrite in the aquifer matrix, and (ii) the associated release of protons (H⁺) induces the dissolution of dolomite as a buffering reaction, which (iii) enhances the accessibility of the injectant to intercrystalline and incorporated sulfurized organic matter within dolomite, causing the release of Mo.

Determination of 93Mo in Radioactive Samples of Sulfuric Acid Media from Nuclear Facilities

⁹³Mo is an important radionuclide in view of radioactive waste repository because of its long half-life and high mobility in the environment. ⁹³Mo decays by electron capture without any measurable gamma ray emission. The concentration of ⁹³Mo in most of the radioactive waste is many orders of magnitude lower than the major activation product radionuclides, which makes the accurate determination of ⁹³Mo a big challenge. A new analytical method for the determination of ⁹³Mo in sulfuric acid media from nuclear power reactor was developed. ⁹³Mo was separated from most of the radionuclides by cation exchange chromatography followed by the removal of sulfate by CaSO₄ precipitation. A further purification of ⁹³Mo, especially from anion species of ⁵¹Cr and ¹²⁵Sb, was achieved by anion exchange chromatography and a short alumina column separation. The chemical yield of ⁹³Mo in the entire separation procedure reached about 75%, and the decontamination factors for all potential interfering radionuclides were 1.5 × 10⁶-1.6 × 10⁸. The purified ⁹³Mo was measured by liquid scintillation counting through counting its low-energy Auger electrons. A detection limit of 2 mBq/g for ⁹³Mo in 50 g sample was achieved by this method, which enables the quantitative determination of ⁹³Mo in most of the radioactive samples in the decommissioning waste and coolant water of nuclear power reactors. The developed method has been successfully applied to determine ⁹³Mo in coolant water of nuclear power reactors, providing a robust analytical approach of ⁹³Mo for the radiological characterization of radioactive wastes.

Impacts of Mo application on biological nitrogen fixation and diazotrophic communities in a flooded rice-soil system

Molybdenum (Mo) deficiency in the farmland of China may limit biological nitrogen fixation (BNF), however, the impact of Mo application on BNF capacities and diazotrophic communities in rice-soil systems is unclear. In this experiment, treatments in a 6.7 atom% ¹⁵N₂-labelling field-based growth chamber for 74 days and treatments in a 99 atom% ¹⁵N₂-labelling microcosm experiment for 40 days combined with 16S rRNA gene sequencing and DNA-stable isotope probing (SIP) were used to investigate the impacts of Mo application on BNF and diazotrophic communities. Our results showed that under the condition that no nitrogen (N) fertilizer was applied, Mo application (500 g sodium molybdate ha^-1) significantly increased N₂ fixation in a rice-Inceptisol system, from 22.3 to 53.1 kg N ha^-1. Mo application significantly increased the number of nifH gene copies and the relative abundance of cyanobacteria in both growth chamber and microcosm experiments. Among cyanobacteria, the relative abundances of the most abundant genera Leptolyngbya and Microcoleus were significantly increased by Mo application. ¹⁵N₂-DNA-SIP further demonstrated that Leptolyngbya and Microcoleus incorporated ¹⁵N_2. Mo application greatly increased BNF in Mo-deficient paddy field (≤0.068 mg kg^-1) and stimulated the growth of cyanobacteria. These results indicated that Mo application in Mo-deficient paddy field could be a useful measure to increase soil N input under no N fertilization.

Early photosynthetic eukaryotes inhabited low-salinity habitats

The early evolutionary history of the chloroplast lineage remains an open question. It is widely accepted that the endosymbiosis that established the chloroplast lineage in eukaryotes can be traced back to a single event, in which a cyanobacterium was incorporated into a protistan host. It is still unclear, however, which Cyanobacteria are most closely related to the chloroplast, when the plastid lineage first evolved, and in what habitats this endosymbiotic event occurred. We present phylogenomic and molecular clock analyses, including data from cyanobacterial and chloroplast genomes using a Bayesian approach, with the aim of estimating the age for the primary endosymbiotic event, the ages of crown groups for photosynthetic eukaryotes, and the independent incorporation of a cyanobacterial endosymbiont by Paulinella Our analyses include both broad taxon sampling (119 taxa) and 18 fossil calibrations across all Cyanobacteria and photosynthetic eukaryotes. Phylogenomic analyses support the hypothesis that the chloroplast lineage diverged from its closet relative Gloeomargarita, a basal cyanobacterial lineage, ∼2.1 billion y ago (Bya). Our analyses suggest that the Archaeplastida, consisting of glaucophytes, red algae, green algae, and land plants, share a common ancestor that lived ∼1.9 Bya. Whereas crown group Rhodophyta evolved in the Mesoproterozoic Era (1,600-1,000 Mya), crown groups Chlorophyta and Streptophyta began to radiate early in the Neoproterozoic (1,000-542 Mya). Stochastic mapping analyses indicate that the first endosymbiotic event occurred in low-salinity environments. Both red and green algae colonized marine environments early in their histories, with prasinophyte green phytoplankton diversifying 850-650 Mya.