Effects of Fe(III) (hydr)oxide mineralogy on the development of microbial communities originating from soil, surface water, groundwater, and aerosols

Reduction of antimony bioavailability with the application of stable exogenous organic matter: a comparative study between rice straw and manure compost

Considering the widespread use of organic amendments to improve soil quality and enhance soil carbon sequestration, it is crucial to understand their impact on the bioavailability of metalloids in soils. Antimony (Sb), a priority pollutant, is particularly impacted by organic matter, yet the effects of different organic amendments-varying in stability and composition-on Sb bioavailability remain unclear. This study investigates the influence of different organic amendments, rice straw and compost, on Sb bioavailability in the rice-soil system, with rice ingestion being a major Sb exposure pathway in humans. Results show that while both amendments increased dissolved organic carbon in soil solution, their effects on Sb bioavailability differed markedly. Rice straw increased CDGT-SbIII by 13.24 %-66.63 %, whereas compost decreased CDGT-SbIII by 32.47 %-43.51 %. These differences were also reflected in Sb accumulation in rice shoots, where compost application resulted in lower Sb content. This reduction may be attributed to increased microbial genera such as Ramlibacter and Sphingomonas, which are associated with SbIII oxidation. Conversely, organic matter with low stability, prone to rapid degradation, could promote reducing soil conditions, thereby increasing SbIII concentrations. Our findings suggest that stable exogenous organic matter, such as pre-decomposed compost, is preferable for managing Sb-contaminated soils.

Integrating microbial community dynamics and emerging contaminants (ECs) for precisely quantifying the sources in groundwater affected by livestock farming

Livestock farming is a major emission source of emerging contaminants (ECs); improper management of ECs could lead to severe groundwater pollution. However, research on accurately controlling the impact of large-scale livestock pollution in groundwater and quantifying sources of ECs pollution from livestock farming to formulating effective control measures is scarce. For the first time, the groundwater near four livestock farms (broiler, dairy, aquaculture, and pig farms) was selected as the research object to characterize the ECs, analyze the impact of ECs on microbial communities, and identify the pollution sources of livestock groundwater by the fast expectation-maximization of microbial source tracking (FEAST). Significant differences in the levels of antibiotics and hormones from four livestock farms led to changes in the groundwater microbial communities. The ECs improved the uniqueness of source biomarkers, providing better help for FEAST distinguishing livestock pollution sources at various groundwater mixing ratios. This study improved the accuracy of FEAST in investigating the pollution sources in groundwater and provided experimental evidence for accurate source tracking of ECs in groundwater in large-scale areas heavily polluted by livestock farming.

Primary Fe-(hydr)oxides and pyrite as carriers of arsenic and antimony: an overlooked problem in acid mine drainage areas

Unusual abundances of pyrite and goethite/hematite occur in quartzite quarries located in the Holy Cross Mountains (south-central Poland). Disseminated arsenical pyrite microcrystals and As/Sb-rich iron-(hydr)oxide accumulations, scarce scorodite (FeAsO4⋅H2O), and traces of löllingite (FeAs2) make up stratiform mineralization zones within an Upper Cambrian siliciclastic-volcanogenic formation. The abundances of arsenic and antimony vary over several orders of magnitude within alternating sandstone and clayey-silty shale beds, which is best evidenced in the Podwiśniówka bedrock (range of 40.4 to 5946 mg/kg As and < 0.01 to 125 mg/kg Sb). Fe-(hydr)oxides are typically more enriched in these two metalloids than microcrystalline pyrite, for example in the Podwiśniówka quarry mean contents of As in Fe-(hydr)oxides and pyrite microcrystals are 2.81 and 1.86 wt% whereas those of Sb are 0.40 and <0.015 wt%, respectively (based on EMP measurements). However, in another subordinate goethite type, mean contents of As and Sb are even higher amounting to 5.92 wt% and 11.40 wt%, respectively. In contrast to poorly soluble goethite/hematite, oxidation of microcrystalline pyrite easily releases arsenic into ponds, pools and seeps. A goethite/hematite crystal structure impedes liberation of As and Sb, which is well documented by trace concentrations of Sb (<1 μg/L) in most examined waters. As opposed to arsenical pyrite, the presence of high contents of As and partly Sb in goethite/hematite has so far been an overlooked problem. Although these two potentially toxic elements are not easily released from Fe-(hydr)oxides, their occurrence in rocks may pose a risk to miners and local residents that may inhale wind-borne mineral particles originating from erosion, mining and rock processing.

Dual role of organic matter in Feammox-driven nitrogen and phosphate removal

Feammox is a novel microbial process that enables simultaneous nitrogen and phosphorus removal in wastewater treatment. This study investigated the role of organic matter in Feammox-driven nutrient removal during long-term bioreactor operation by gradually increasing the influent chemical oxygen demand (COD) concentration from 0 to 50, and then to 100 mg/L. The results revealed that the ammonium removal efficiency was reduced from 60.5 % to 20.7 % with COD concentration increasing from 0 to 100 mg/L. In contrast, organic matter enhanced nitrate removal through heterotrophic denitrification, which outcompeted nitrate-dependent Fe(II) oxidation. Phosphorus removal was increased up to approximately 90 % via Fe(II)-mediated precipitation, forming vivianite crystals, evidenced by X-ray diffraction analysis. Continuous addition of Fe(III) alleviated the inhibitory effect of organic matter on ammonia oxidation by serving as an alternative electron acceptor, reducing competition. Therefore, optimizing organic matter levels and ensuring sufficient Fe(III) availability are crucial for achieving efficient nutrient removal in Feammox systems, particularly for treating wastewater with a low carbon/nitrogen ratio.

Microbial Fe(III) reduction across a pH gradient: The impacts on secondary mineralization and microbial community development

Fe(III) (hydr)oxides are prevalent in natural environments where they impact contaminant mobility, greenhouse gas release, and nutrient cycling. In anoxic conditions, dissimilatory iron reducing bacteria (DIRB) and other microbial groups primarily drive Fe(III) reduction. Dissimilatory iron reduction (DIR) results in the reductive dissolution of Fe(III) phases and subsequent secondary mineralization. These processes are highly sensitive to pH changes, since protons serve as reactants in DIR. However, there is limited understanding of how DIR impacts secondary mineralization and microbial community development under relevant pH gradients. This study investigated the impact of initial pH (6.3, 6.9, 7.3, 7.7, 9) and Fe(III) source (goethite, lepidocrocite) on DIR, using acetate as the electron donor. The rate and extent of Fe(III) reduction decreased with increasing pH and that lepidocrocite, with its relatively lower crystallinity compared to goethite, supported greater DIR activity. Solid phase analyses revealed predominant formation of siderite alongside lepidocrocite reduction in microcosms with initial pH at 6.3 and 6.9. Similarly, in microcosms with initial pH at 7.3 and 7.7, partial transformation to siderite occurred. In contrast, goethite-amended microcosms did not show clear mineralogical transformations, despite the observed Fe(II) production. Microbial community analysis using 16S rRNA sequencing indicated greater enrichment of DIRB at lower pH, with a decline in abundance as pH increased. Overall, pH influenced DIR more than Fe mineralogy, highlighting its critical role in DIR processes, secondary mineral formation, and DIRB community development. This study further provides insights for developing remediation strategies involving microbial Fe(III) reduction under varying pH conditions.

Study on the mechanism of regulating micromolar Fe utilization and promoting denitrification by guanosine monophosphate (GMP) based multi-signal functional material Hematin@Fe/GMP

A novel multi-signal functional material consisting of Hematin, Fe, and guanosine monophosphate (GMP) was successfully constructed (Hematin@Fe/GMP) to enhance denitrification efficiency based on the signal network regulation of electron transfer, micromolar Fe utilization, and microbial community. Hematin@Fe/GMP enhanced nitrate reduction rate by 2.33-fold with a 9.9 mg L-1 h-1 reduction rate. The mechanisms of accelerated denitrification were elaborated deeply from the electrochemical experiments, microbial metabolism activity, key enzyme activity, gene expression, and microbial community. Specifically, electrochemical experiments and X-ray photoelectron spectroscopy demonstrated that the released redox signal (Fe2+/Fe3+) promoted the increased redox substances (extracellular polymeric substances, cytochrome c, and riboflavin) to accelerate electron transfer efficiency. Metagenomic analysis suggested the released Fe utilization signal modulated siderophores genes (fhuB, fhuC, and fhuD) to promote the uptake and utilization of micromolar Fe, which was more conducive to synthesizing cytochrome c. Moreover, extracellular polymeric substances (EPS) stripping experiments demonstrated that the membrane-anchored cyt-c could shuttle in EPS and bind with Hematin@Fe/GMP to form an electrical conduit for accelerating denitrification efficiency. In inhibition experiments, Hematin@Fe/GMP could break down electron transfer barriers and restore/compensate for the electron transfer chain. Meanwhile, Hematin@Fe/GMP could restore the electrical signal disruption and synergize with the enriched signaling-capable microorganisms (Stutzerimonas and Thauera) to regulate quorum sensing. This research introduced multi-signal modulation of Hematin@Fe/GMP on denitrification and provided strategies for accelerating the biological transformation process and effectively utilizing micromolar Fe in practical applications.

Fe/GMP functional nanomaterial enhancing the denitrification efficiency by bi-signal regulation: Electron transfer and microbial community

A novel functional nanomaterial composed of guanosine monophosphate (GMP) and Fe enhanced denitrification efficiency by regulating electron transfer and microbial community. Fe/GMP enhanced nitrate (NO3-) degradation rates by 3.00-fold in serum vial batch experiments, with a rate constant of 17.39 mg/(L·h) in sequencing batch reactor. Fe/GMP-mediated interface promoted the secretion of redox-active substances in the extracellular polymeric substances to enhance the extracellular electron transfer. Specifically, Fe/GMP regulated electron transfer and metabolism activity by dynamic conversion of Fe3+/Fe2+ redox signal. Additionally, enzyme activity assays verified the optimized electron distribution function of Fe/GMP and thus enhanced intracellular electron transfer. High-throughput sequencing confirmed Fe/GMP selectively enriched microorganisms (especially Thauera 50.70 %). The tetraethylammonium stress experiment demonstrated Fe/GMP as an exogenous signaling molecule to restore microbial communication for microbial community regulation. The study proposes a multifaceted synergistic mechanism based on the repeater function of Fe/GMP in denitrification and offers insights for practical applications.

Anaerobic microbial metabolism in soil columns affected by highly alkaline pH: Implication for biogeochemistry near construction and demolition waste disposal sites

Construction and demolition wastes (CDWs) have become a significant environmental concern due to urbanization. CDWs in landfill sites can generate high-pH leachate and various constituents (e.g., acetate and sulfate) following the dissolution of cement material, which may affect subsurface biogeochemical properties. However, the impact of CDW leachate on microbial reactions and community compositions in subsurface environments remains unclear. Therefore, we created columns composed of layers of concrete debris containing-soil (CDS) and underlying CDW-free soil, and fed them artificial groundwater with or without acetate and/or sulfate. In all columns, the initial pH 5.6 of the underlying soil layer rapidly increased to 10.8 (without acetate and sulfate), 10.1 (with sulfate), 10.1 (with acetate), and 8.3 (with acetate and sulfate) within 35 days. Alkaliphilic or alkaline-resistant microbes including Hydrogenophaga, Silanimonas, Algoriphagus, and/or Dethiobacter were dominant throughout the incubation in all columns, and their relative abundance was highest in the column without acetate and sulfate (50.7-86.6%). Fe(III) and sulfate reduction did not occur in the underlying soil layer without acetate. However, in the column with acetate alone, pH was decreased to 9.9 after day 85 and Fe(II) was produced with an increase in the relative abundance of Fe(III)-reducing bacteria up to 9.1%, followed by an increase in the methanogenic archaea Methanosarcina, suggestive of methanogenesis. In the column with both acetate and sulfate, Fe(III) and sulfate reduction occurred along with an increase in both Fe(III)- and sulfate-reducing bacteria (19.1 and 17.7%, respectively), while Methanosarcina appeared later. The results demonstrate that microbial Fe(III)- and sulfate-reduction and acetoclastic methanogenesis can occur even in soils with highly alkaline pH resulting from the dissolution of concrete debris.