In urbanized areas, extracellular DNA (exDNA) is suspected of carrying genes with undesirable traits like virulence genes (VGs) or antibiotic resistance genes (ARGs), which can spread through horizontal gene transfer (HGT). Hence, it is crucial to develop novel approaches for the mitigation of exDNA in the environment. Our research explores the role of goethite, a common iron mineral with high adsorption capabilities, in exDNA adsorption processes. We compare well-crystalline, semi-crystalline, and nano goethites with varying particle sizes to achieve various specific surface areas (SSAs) (18.7-161.6 m2/g) and porosities. We conducted batch adsorption experiments using DNA molecules of varying chain lengths (DNA sizes: <11 Kb, <6 Kb, and <3 Kb) and assessed the impact of Ca2+ and biomacromolecules on the adsorption efficacy and mechanisms. Results show that porosity and pore structure significantly influence DNA adsorption capacity. Goethite with well-developed meso- and macroporosity demonstrated enhanced DNA adsorption. The accumulation of DNA on the goethite interface led to substantial aggregation in the system, thus the formation of DNA-goethite conjugates, indicating the bridging between mineral particles. DNA chain length, the presence of Ca2+, and the biomacromolecule matrix also affected the adsorption capacity and mechanism. Interactions between DNA and positively charged biomacromolecules or Ca2+ led to DNA compaction, allowing greater DNA accumulation in pores. However, a high concentration of biomacromolecules led to the saturation of the goethite surface, inhibiting DNA adsorption. AFM imaging of goethite particles after adsorption suggested the formation of the DNA multilayer. The study advances understanding of the environmental behavior of exDNA and its interaction with iron oxyhydroxides, offering insights into developing more effective methods for ARGs removal in wastewater treatment plants. By manipulating the textural properties of goethite, it\'s possible to enhance exDNA removal, potentially reducing the spread of biocontamination in urban and industrial environments.

Oxides of silicon (Si), manganese (Mn), and zinc (Zn) have been used as soil amendments to reduce As mobility and uptake in paddy soil systems. However, these amendments are hypothesized to be affected differently depending on the soil pH and their effect on As speciation in rice paddy systems is not fully understood. Herein, we used a microcosm experiment to investigate the effects of natural Si-rich fly ash and synthetic Mn and Zn oxides on the temporal development of porewater chemistry, including aqueous As speciation (As(III), As(V), MMA, DMA, and DMMTA) and solid-phase As solubility, in a naturally calcareous soil with or without soil acidification (with sulfuric acid) during 28 days of flooding and subsequent 14 days of drainage. We found that soil acidification to pH 4.5 considerably increased the solubility of Si, Fe, Mn, and Zn compared to the non-acidified soil. Additions of Mn and Zn oxides decreased the concentrations of dissolved arsenite and arsenate in the non-acidified soil whereas additions of Zn oxide and combined Si-Zn oxides increased them in the acidified soil. The Si-rich fly ash did not increase dissolved Si and As in the acidified and non-acidified soils. Dimethylated monothioarsenate (DMMTA) was mainly observed in the acidified soil during the later stage of soil flooding. The initial 28 days of soil flooding decreased the levels of soluble and exchangeable As and increased As associated with Mn oxides, whereas the subsequent 14 days of soil drainage reversed the trend. This study highlighted that soil acidification considerably controlled the solubilization of Ca and Fe, thus influencing the soil pH-Eh buffering capacity, the solubility of Si, Mn, and Zn oxides, and the mobility of different As species in carbonate-rich and acidic soils under redox fluctuations.

In waterlogged soils, iron plaque forms a reactive barrier between the root and soil, collecting phosphate and metals such as arsenic and cadmium. It is well established that iron-reducing bacteria solubilize iron, releasing these associated elements. In contrast, microbial roles in plaque formation have not been clear. Here, we show that there is a substantial population of iron oxidizers in plaque, and furthermore, that these organisms (Sideroxydans and Gallionella) are distinguished by genes for plant colonization and nutrient fixation. Our results suggest that iron-oxidizing and iron-reducing bacteria form and remodel iron plaque, making it a dynamic system that represents both a temporary sink for elements (P, As, Cd, C, etc.) as well as a source. In contrast to abiotic iron oxidation, microbial iron oxidation results in coupled Fe-C-N cycling, as well as microbe-microbe and microbe-plant ecological interactions that need to be considered in soil biogeochemistry, ecosystem dynamics, and crop management.

The interfacial electron transfer (ET) between electron shuttling compounds and iron (Fe) oxyhydroxides plays a crucial role in the reductive dissolution of Fe minerals and the fate of surface-bound arsenic (As). However, the impact of exposed facets of highly crystalline hematite on reductive dissolution and As immobilization is poorly understood. In this study, we systematically investigated the interfacial processes of the electron shuttling compound cysteine (Cys) on various facets of hematite and the reallocations of surface-bound As(III) or As(V) on the respective surfaces. Our results demonstrate that the ET process between Cys and hematite generates Fe(II) and leads to reductive dissolution, with more Fe(II) generated on {001} facets of exposed hematite nanoplates (HNPs). Reductive dissolution of hematite leads to significantly enhanced As(V) reallocations on hematite. Nevertheless, upon the addition of Cys, a raipd release of As(III) can be halted by its prompt re-adsorption, leaving the extent of As(III) immobilization on hematite unchanged throughout the course of reductive dissolution. This is due to that Fe(II) can form new precipitates with As(V), a process that is facet-dependent and influenced by water chemistry. Electrochemical analysis reveals that HNPs exhibit higher conductivity and ET ability, which is beneficial for reductive dissolution and As reallocations on hematite. These findings highlight the facet-dependent reallocations of As(III) and As(V) facilitated by electron shuttling compounds and have implications for the biogeochemical processes of As in soil and subsurface environments.

Iron minerals, such as iron oxides and iron oxyhydroxides, are the main influential soil components in catalyzed hydrogen peroxide propagation (CHP). Due to their dual effects on H2O2 activation to produce reactive oxygen species (ROS) and invalid consumption to produce oxygen, the intrinsic reactivity of iron minerals toward H2O2 decomposition requires comprehensive investigations. Herein, six iron minerals (hematite, magnetite, maghemite, goethite, feroxyhyte, and ferrihydrite) for H2O2 decomposition were investigated by a combination of normalized kinetic rate constants of H2O2 decomposition (NkH2O2), O2 production (NkO2), benzoic acid degradation (NkBA), and hexachloroethane degradation (NkHCA) over the surface area of each mineral. The results indicate H2O2 decomposition over iron minerals is a surface-related heterogeneous process. Hematite and goethite are the most promising minerals for environmental cleanup in terms of ROS production, because their H2O2 utilization efficiency for benzoic acid (BA) degradation (0.138 and 0.024 mol BA/mol H2O2 for hematite and goethite, respectively) are highest among the six iron minerals. Magnetite and maghemite are highly active for both H2O2 decomposition and O2 production at neutral and basic pHs. The presence of organic compounds suppresses O2 production by more than 60%, which favors H2O2 utilization. Ferrihydrite and feroxyhyte are considered as the problematic mineral for CHP due to that the two minerals acquire a high O2 production and negligible ROS generation at all pHs. The results of this study provide new insights to increase the understandings of H2O2-iron mineral systems and guide the application of iron minerals in chemical oxidation technologies.

Iron hydroxides are ubiquitous in soils and aquifers and have been adopted as adsorbents for As(V) removal. However, the complexation mechanisms of As(V) have not been well understood due to the lack of information on the reactive sites and acidities of iron hydroxides. In this work, we first calculated the acidity constants (pKas) of surface groups on lepidocrocite (010), (001), and (100) surfaces by using the first-principles molecular dynamics (FPMD)-based vertical energy gap method. Then, the desorption free energies of As(V) on goethite (110) and lepidocrocite (001) surfaces were calculated by using constrained FPMD simulations. The point of zero charges and reactive sites of individual surfaces were obtained based on the calculated pKas. The structures, thermodynamics, and pH dependence for As(V) complexation were derived by integrating the pKas and desorption free energies. The pKa data sets obtained are fundamental parameters that control the charging and adsorption behavior of iron oxyhydroxides and will be very useful in investigating the adsorption processes on these minerals. The pH-dependent complexation mechanisms of As(V) derived in this study would be helpful for the development of effective adsorbent materials and the prediction of the long-term behavior of As(V) in natural environments.

Iron (Fe) oxyhydroxides provide many functions in soils, mainly owing to their large surface area and high surface charge density. The reactivity of Fe oxyhydroxides is function of their mineralogical characteristics (e.g., crystallinity degree and crystal size). Detailed studies of these features are essential for predicting the stability and reactivity of these minerals within soil and sediments. The present study aimed to evaluate geochemical changes in Fe-rich tailings after the world\'s largest mining disaster in SE Brazil (in 2015) and to predict the potential environmental implications for the estuary. The mineralogical characteristics of the tailings were studied at three different times (2015, 2107, and 2019) to assess how an active redox environment affects Fe oxyhydroxides and to estimate the time frame within which significant changes occur. The study findings indicate a large decrease in the Fe oxyhydroxides crystallinity, which were initially composed (93%) of highly crystalline Fe oxyhydroxides (i.e., goethite and hematite) and 6.7% of poorly crystalline Fe oxyhydroxides (i.e., lepidocrocite and ferrihydrite). Within 4 years the mineralogical features of Fe oxyhydroxides had shifted, and in 2019 poorly crystalline Fe oxyhydroxides represented 47% of the Fe forms. Scanning electron microscope micrographs and the mean crystal size evidenced a decrease in particle size from 109 nm to 49 nm for goethite in the d111 direction. The changes in mean crystal size increased the reactivity of Fe oxyhydroxides, resulting in a greater number of interactions with cationic and anionic species. The decreased crystallinity and increased reactivity led to the compounds being more susceptible to reductive dissolution. Overall, the findings show that the decrease in crystallinity along with higher susceptibility to reductive dissolution of Fe oxyhydroxides can affect the fate of environmentally detrimental elements (e.g., phosphorus and trace metals) thereby increasing the concentration of these pollutants in estuarine soils and waters.

The scavenging of soluble metals by iron (Fe) and aluminium (Al) oxyhydroxides is a natural process that occurs in acid mine drainage (AMD). This phenomenon is relevant to the immobilization, transport, and recovery of important natural resources such as rare earth elements (REE) and uranium (U). Furthermore, understanding the players and the reactions that govern the scavenging of REE and U by Fe and Al oxyhydroxides in aqueous systems is fundamental for natural and engineering sciences and for environmental management. In this scenario, the current work investigated the role of iron in the co-precipitation of REE and U when treating effluents by pH neutralization in an AMD system located in Brazil. The research employed water sampling, co-precipitation batch experiments, sequential extraction, X-ray diffraction and 57Fe Mössbauer spectroscopy. The results revealed that the presence and the amount of Fe in the initial solution can influence the REE removal efficiency positively. The effect of the addition of Fe over the REE removal efficiency was irrelevant when the pH of the AMD was raised to values equal to 7-8. The scavenging of U was not influenced by the addition of Fe to the AMD. The sequential extraction results showed that precipitates containing higher amounts of Fe tend to be less labile. The 57Fe Mössbauer spectra revealed that the REE can occupy iron sites in the structure of the amorphous precipitates. The findings of the current study can be extrapolated to other AMD systems and contribute to the development of novel REE recovery and hydrometallurgical techniques.

The presence of arsenic (As) in the sediment and the particulate and dissolved fractions of the water column determines its behavior and bioavailability. The main geochemical parameters responsible for As mobility are organic matter and oxide-forming metals such as Fe. The As distribution and its concentration were evaluated in the dissolved fraction, suspended particulate matter (SPM) and sediment of the lower Paraíba do Sul River (PSR), its main tributaries (Muriaé, Pomba, and Dois Rios rivers), and flooded and estuarine areas. As was not detected in the dissolved fraction. The river flow influenced the As concentration in the SPM, which was higher in the dry season than in the rainy season (2.6 ± 0.69 and 1.98 ± 0.29 mg kg-1, respectively). The Fe oxyhydroxides, organic carbon, and surface area measured in the sediment were positively related with As concentration (R2 = 0.11, 0.34, and 0.30; p < 0.05). The highest As concentrations in the sediment occurred in the secondary estuary and flooded areas (5.16 ± 4.78 and 1.23 ± 0.44 mg kg-1, respectively), in which finer granulometric fractions (silt and clay) predominated (64% and 71%, respectively), in addition to greater surface area. The measurement of stable carbon and nitrogen isotopes (δ13C and δ15N) and atomic ratio (C:N)a indicated the existence of a combination of autochthonous and allochthonous sources of organic matter composing the SPM. In general, the As concentrations in the sediment and SPM were low, with values below that permitted by Brazilian regulations (5.9 mg kg-1), which suggests that the As sources in the lower basin of the PSR are diffuse and natural.

Investigating uranium migration mechanisms related to the weathering of waste rocks is essential for developing strategies that can address the potential environmental issues caused by uranium mining. This work is based on environmental samples containing 2 L ferrihydrite, lepidocrocite and goethite collected in the technosols from granitic waste rock piles, mine drainage conduits and mine waters. The results show the important role of iron oxyhydroxide in U immobilization and re-concentration. EXAFS spectroscopy combined with mineralogical and geochemical studies (Scanning electronic microscopy, Wavelength-dispersive X-ray spectroscopy microprobe, inductively coupled plasma - optical emission spectrometry/mass spectrometry and X-ray diffraction) allowed for the identification of uranyl ternary surface complexes at the ferrihydrite surface that were either composed of phosphate groups or organic matter. Moreover, goethite and lepidocrocite were also identified as a secondary trap for U immobilization. U(VI) is known to be mobile in oxidizing conditions. This study highlights the control of the uranyl mobility by various iron oxyhydroxides in supergene conditions.