Metal cation saturation on montmorillonites facilitates the adsorption of DNA via cation bridging

Micro-interfacial behavior of antibiotic-resistant bacteria and antibiotic resistance genes in the soil environment: A review

Overutilization and misuse of antibiotics in recent decades markedly intensified the rapid proliferation and diffusion of antibiotic resistance genes (ARGs) within the environment, thereby elevating ARGs to the status of a global public health crisis. Recognizing that soil acts as a critical reservoir for ARGs, environmental researchers have made great progress in exploring the sources, distribution, and spread of ARGs in soil. However, the microscopic state and micro-interfacial behavior of ARGs in soil remains inadequately understood. In this study, we reviewed the micro-interfacial behaviors of antibiotic-resistant bacteria (ARB) in soil and porous media, predominantly including migration-deposition, adsorption, and biofilm formation. Meanwhile, adsorption, proliferation, and degradation were identified as the primary micro-interfacial behaviors of ARGs in the soil, with component of soil serving as significant determinant. Our work contributes to the further comprehension of the microstates and processes of ARB and ARGs in the soil environments and offers a theoretical foundation for managing and mitigating the risks associated with ARG contamination.

Plasmid size determines adsorption to clay and breakthrough in a saturated sand column

Horizontal gene transfer (HGT) is a major factor in the spread of antibiotic resistant genes (ARG). Transformation, one mode of HGT, involves the acquisition and expression of extracellular DNA (eDNA). eDNA in soils is degraded rapidly by extracellular nucleases. However, if bound to a clay particle, eDNA can persist for long periods of time without losing its transformation ability. To better understand the mechanism of eDNA persistence in soil, this experiment assessed the effects of 1) clay mineralogy, 2) mixed salt solution, 3) plasmid size on DNA adsorption to clay and 4) breakthrough behavior of three differently sized plasmids in an environmentally relevant solution. Batch test methods were used to determine adsorption trends of three differently sized DNA plasmids, pUC19, pBR322, and pTYB21, to several pure clay minerals, goethite (α-FeOOH), illite, and kaolinite, and one environmental soil sample. Results show not all sorbents have equal adsorption capacity based on surface area with adsorption capacities decreasing from goethite > illite = kaolinite > bulk soil, and low ionic strength solutions will likely not significantly alter sorption trends. Additionally, plasmid DNA size (i.e., length) was shown to be a significant predictor of adsorption efficiency and that size affects DNA breakthrough, with breakthroughs occurring later with larger plasmids. Given that DNA persistence is linked to its adsorption to soil constituents and breakthrough, eDNA size is likely an important contributor to the spread of ARG within natural microbial communities.

Formation of cation bridges and its promoting mechanism for sorption of sulfamethoxazole by montmorillonite

The coexistence of metal cations is often accompanied by organic pollution and could affect the environmental fate of organics by mediating the formation of cation bridges. However, the environmental fate and risk of organics in cation co-existing environments are poorly understood due to the lack of accurate identification of cation bridge formation and stability. In this study, the sorption of sulfamethoxazole (SMX) on montmorillonite (MT) with the coexistence of three different valence metal cations (Na+, Ca2+, and Cr3+) was investigated. Ca2+ and Cr3+ can significantly promote the sorption of SMX on MT for about 5∼10 times promotion, respectively, while Na+ bridges displayed little effect on the sorption of SMX. The sorption binding energy of SMX with MT-Ca (-44.01 kcal/mol) and MT-Cr (-64.57 kcal/mol) bridges was significantly lower than that with MT-Na (-38.45 kcal/mol) and MT (-39.39 kcal/mol), indicating that the sorption affinity of SMX on Cr and Ca bridges was much stronger. The higher valence of the cations also resulted in a more stable adsorbed SMX with less desorption fluctuation. In addition, the relatively higher initial concentration of SMX and the valence of cations increased the bonding density of the cation bridges, thus promoting the apparent sorption of SMX on MT to a certain extent. This work reveals the formation and function of cation bridges in the sorption of SMX on MT. It lays a theoretical foundation for further understanding the environmental fate and risk of organics.

Synergetic effects of Mn(II) production and site availability on arsenite oxidation and arsenate adsorption on birnessite in the presence of low molecular weight organic acids

Manganese oxides and organic acids are key factors affecting arsenic mobility, but As(III) oxidation and adsorption in the coexistence of birnessite and low molecular weight organic acids (LMWOAs) are poorly understood. Herein, As(III) immobilization by birnessite was investigated with/without LMWOAs (including tartaric (TA), malate (MA), and succinic acids (SA) with two, one and zero hydroxyl groups, respectively). In the low-As(III) system with less Mn(II) production, LMWOAs generally inhibited As(III) oxidation. The slower decrease in As(III) concentration in TA-amended batches resulted from stronger bonding interaction between TA and edge sites, evidenced by higher removal of TA than MA and SA in solutions and the higher proportion of shifted C-OH component in solids. In high-As(III) systems with abundant Mn(II) production, higher concentrations of dissolved Mn and Mn(III) in LMWOA-amended batches than in LMWOA-free batches revealed that LMWOA-induced complexing dissolution caused the release of adsorbed Mn(II), which was conducive to As(III) oxidation and As(V) adsorption onto the edge sites. The lowest concentrations of dissolved Mn and Mn(III) in TA-amended batches indicated that the hydroxyl group constrained complexing dissolution. This study reveals that concentrations of produced Mn(II) determined the roles of LMWOAs in As(III) behavior and highlights the impacts of the hydroxyl group on arsenic mobility.

Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms

Soil, the largest terrestrial carbon reservoir, is central to climate change and relevant feedback to environmental health. Minerals are the essential components that contribute to over 60% of soil carbon storage. However, how the interactions between minerals and organic carbon shape the carbon transformation and stability remains poorly understood. Herein, we critically review the primary interactions between organic carbon and soil minerals and the relevant mechanisms, including sorption, redox reaction, co-precipitation, dissolution, polymerization, and catalytic reaction. These interactions, highly complex with the combination of multiple processes, greatly affect the stability of organic carbon through the following processes: (1) formation or deconstruction of the mineral-organic carbon association; (2) oxidative transformation of the organic carbon with minerals; (3) catalytic polymerization of organic carbon with minerals; and (4) varying association stability of organic carbon according to the mineral transformation. Several pieces of evidence related to the carbon turnover and stability during the interaction with soil minerals in the real eco-environment are then demonstrated. We also highlight the current research gaps and outline research priorities, which may map future directions for a deeper mechanisms-based understanding of the soil carbon storage capacity considering its interactions with minerals.

New discovery of extremely high adsorption of environmental DNA on cuttlefish bone pyrolysis derivative via large pore structure and carbon film

Environmental DNA (eDNA) carrying antibiotic resistance gene (ARG) has attracted a great deal of attention because of its threat to the ecology and human health. Traditional porous adsorbents, such as microporous biochar and natural mineral, are low-effective in removing eDNA from sewage. This study used cuttlefish-bone (CB), a fishery waste, as an anticipated material to adsorb a model compound of eDNA from herring sperm (hsDNA). An interesting result was firstly observed that extremely high DNA adsorption on cuttlefish-bone pyrolysis derivative (CCB) was up to 88.7 mg/g, 3-10 folds higher than that of most other adsorbents in the existing literatures, which was attributed to the carbon film and large pores. To achieve an adsorption rate of 75 %, hsDNA adsorption took 96 h on CB but only 24 h on CCB, which was attributed to the fluent channel of CCB. The ligand exchange, Ca2+ bridge and π-π interaction were identified as dominated adsorption mechanisms, based on FTIR and phosphate competition experiments. This study exploited a high-efficient, environmentally friendly, and low-cost adsorbent for treating ARG-contaminated soil and water.

Electrostatic coupling and water bridging in adsorption hierarchy of biomolecules at water-clay interfaces

Clay minerals are implicated in the retention of biomolecules within organic matter in many soil environments. Spectroscopic studies have proposed several mechanisms for biomolecule adsorption on clays. Here, we employ molecular dynamics simulations to investigate these mechanisms in hydrated adsorbate conformations of montmorillonite, a smectite-type clay, with ten biomolecules of varying chemistry and structure, including sugars related to cellulose and hemicellulose, lignin-related phenolic acid, and amino acids with different functional groups. Our molecular modeling captures biomolecule-clay and biomolecule-biomolecule interactions that dictate selectivity and competition in adsorption retention and interlayer nanopore trapping, which we determine experimentally by NMR and X-ray diffraction, respectively. Specific adsorbate structures are important in facilitating the electrostatic attraction and Van der Waals energies underlying the hierarchy in biomolecule adsorption. Stabilized by a network of direct and water-bridged hydrogen bonds, favorable electrostatic interactions drive this hierarchy whereby amino acids with positively charged side chains are preferentially adsorbed on the negatively charged clay surface compared to the sugars and carboxylate-rich aromatics and amino acids. With divalent metal cations, our model adsorbate conformations illustrate hydrated metal cation bridging of carboxylate-containing biomolecules to the clay surface, thus explaining divalent cation-promoted adsorption from our experimental data. Adsorption experiments with a mixture of biomolecules reveal selective inhibition in biomolecule adsorption, which our molecular modeling attributes to electrostatic biomolecule-biomolecule pairing that is more energetically favorable than the biomolecule-clay complex. In sum, our findings highlight chemical and structural features that can inform hypotheses for predicting biomolecule adsorption at water-clay interfaces.

Revealing the infiltration process and retention mechanisms of surface applied free DNA tracer through soil under flood irrigation

It has been recently demonstrated that free DNA tracers have the potential in tracing water flow and contaminant transport through the vadose zone. However, whether the free DNA tracer can be used in flood irrigation area to track water flow and solute/contaminant transport is still unclear. To reveal the infiltration process and retention mechanisms of surface applied free DNA tracer through soil under flood irrigation, we tested the fate and transport behavior of surface applied free DNA tracers through packed saturated sandy soil columns with a 10 cm water head mimicking flood irrigation. From the experimental breakthrough curves and by fitting a two-site kinetic sorption model (R2 = 0.83-0.91 and NSE = 0.79-0.89), adsorption/desorption rates could be obtained and tracer retention profiles could be simulated. Together these results revealed that 1) the adsorption of free DNA was dominantly to clay particles in the soil, which took up 1.96 % by volume, but took up >97.5 % by surface area and densely cover the surface of sand particles; and 2) at a pore water pH of 8.0, excluding the 4.9 % passing through and 3.1 % degradation amount, the main retention mechanisms in the experimental soil were ligand exchange (42.0 %), Van der Waals interactions (mainly hydrogen bonds), electrostatic forces and straining (together 44.7 %), and cation bridge (5.3 %). To our knowledge, this study is the first to quantify the contribution of each of the main retention mechanisms of free synthetic DNA tracers passing through soil. Our findings could facilitate the application of free DNA tracer to trace vadose zone water flow and solute/contaminant transport under flood irrigation and other infiltration conditions.

Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.

Manganese losses induced by severe soil acidification in the extensive Lei bamboo (Phyllostachys violascens) plantation stands in Eastern China

Manganese (Mn) is a critical element in soils, essential to plant growth. Long-term and intensively managed Lei bamboo (Phyllostachys violascens) stands are usually subjected to severe soil acidification and Mn activation. However, Mn migration from topsoil to deep soil induced by severe soil acidification was poorly recognized and studied. The distribution and changes of the total and the operationally defined Mn forms in soil profiles and its potential stress and environmental effect were investigated in a chronosequence of Lei bamboo stands (0, 2, 6, 11, and 16 years of stand age). The results showed that the Mn amount was significantly decreased in topsoil and accumulated in subsoil with the long-term and intensive fertilizer application. Soil exchangeable Mn and superphosphate extractable Mn demonstrated large different variation to total Mn, whereas their sum was largely higher than and highly correlated with 8-hydroxyquinoline (HQN) extractable Mn. Soil organic carbon, pH value, exchangeable bases, and soil redox simultaneously controlled soil Mn depletion. In conclusion, long-term and intensive fertilizer application leads to soil acidification and accelerated soil Mn depletion in bamboo stand soil, promoting Mn accumulation in bamboo shoots.

Sulfur: a neglected driver of the increased abundance of antibiotic resistance genes in agricultural reclaimed subsidence land located in coal mines with high phreatic water levels

Due to the shallow burial of groundwater in coal mines with a high phreatic water level, a large area of subsidence lakes is formed after the mine collapses. Agricultural and fishery reclamation activities have been carried out, which introduced antibiotics and exacerbated the contamination of antibiotic resistance genes (ARGs), but this has received limited attention. This study analyzed ARG occurrence in reclaimed mining areas, the key impact factors, and the underlying mechanism. The results show that sulfur is the most critical factor impacting the abundance of ARGs in reclaimed soil, which is due to changes in the microbial community. The species and abundance of ARGs in the reclaimed soil were higher than those in the controlled soil. The relative abundances of most ARGs increased with the depth of reclaimed soil (from 0 to 80 cm). In addition, the microbial structures of the reclaimed and controlled soils were significantly different. Proteobacteria, was the most dominant microbial phylum in the reclaimed soil. This difference is likely related to the high abundance of sulfur metabolism functional genes in the reclaimed soil. Correlation analysis showed that the differences in ARGs and microorganisms in the two soil types were highly correlated with the sulfur content. High levels of sulfur promoted the proliferation of sulfur-metabolizing microbial populations such as Proteobacteria and Gemmatimonadetes in the reclaimed soils. Remarkably, these microbial phyla were the main antibiotic-resistant bacteria in this study, and their proliferation created conditions for the enrichment of ARGs. Overall, this study underscores the risk of the abundance and spread of ARGs driven by high-level sulfur in reclaimed soils and reveals the mechanisms.

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems

Widespread antibiotic resistance genes (ARGs) have emerged as a focus of attention for public health. Transformation is essential for ARGs dissemination in soils and associated environments; however, the mechanisms of how soil components contribute to the transformation of ARGs remain elusive. Here we demonstrate that three representative mineral-humic acid (HA) composites exert contrasting influence on the transformation of plasmid-borne ARGs in Bacillus subtilis. Mineral surface-bound HA facilitated transformation in kaolinite and montmorillonite systems, while an inhibitory effect of HA was observed for goethite. The elevated transformation by HA-coated kaolinite was mainly attributed to the enhanced activity of competence-stimulating factor (CSF), while increased transformation by montmorillonite-HA composites was assigned to the weakened adsorption affinity of DNA and enhanced gene expression induced by flagella-driven cell motility. In goethite system, HA played an overriding role in suppressing transformation via alleviation of cell membrane damage. The results obtained offer insights into the divergent mechanisms of humic substances in modulating bacterial transformation by soil minerals. Our findings would help for a better understanding on the fate of ARGs in soil systems and provide potentials for the utilization of soil components, particularly organic matter, to mitigate the spread of ARGs in a range of settings.

Irrigation water quality, gypsum, and city waste compost addition affect P dynamics in saline-sodic soils

The amendments used for sodicity reclamation also profoundly influence P dynamics and leaching losses. This study characterized the effect of irrigation water quality on P dynamics and leaching from saline-sodic soil during reclamation utilizing gypsum alone or in combination with manure and city compost. Changes in properties of unleached and leached soils were fitted with labile P pools using redundancy analysis. The relation between leachate properties and P loss was explained by means of monitoring leachate properties up to ten pore volumes. During incubation, the water-extractable P (P_H2O) concentration was greater than Olsen's P (P_NaHCO3) in all treatments. The P_NaHCO3 decreased in proportion to the amount of gypsum applied. Applying the organics with gypsum increased the P_NaHCO3, P_H2O, and organic P concentration compared to gypsum alone. The labile P pools in soil were positively correlated with HCO₃^- content (r = 0.39-0.77; P < 0.05) of leached and unleached soils. Adding gypsum and compost caused a 10-14% decrease in cumulative P leaching. The cumulative P leaching were greater with rainwater compared to saline water of SAR (sodium adsorption ratio) 5 and 15. The CO₃^2-, HCO₃^-, pH, and SO₄^2-content of the leachate explained about 71% variability in total P leaching (adj. R² = 0.71; P < 0.001). This study concludes that low electrolyte water had a greater risk of P leaching and associated environmental pollution. Leaching of the saline-sodic soil amended with gypsum and city waste compost with low SAR saline water can reduce P leaching compared to good quality rainwater.

The Multiple States of Environmental DNA and What Is Known about Their Persistence in Aquatic Environments

Increased use of environmental DNA (eDNA) analysis for indirect species detection has spurred the need to understand eDNA persistence in the environment. Understanding the persistence of eDNA is complex because it exists in a mixture of different states (e.g., dissolved, particle adsorbed, intracellular, and intraorganellar), and each state is expected to have a specific decay rate that depends on environmental parameters. Thus, improving knowledge about eDNA conversion rates between states and the reactions that degrade eDNA in different states is needed. Here, we focus on eukaryotic extraorganismal eDNA, outline how water chemistry and suspended mineral particles likely affect conversion among each eDNA state, and indicate how environmental parameters affect persistence of states in the water column. On the basis of deducing these controlling parameters, we synthesized the eDNA literature to assess whether we could already derive a general understanding of eDNA states persisting in the environment. However, we found that these parameters are often not being measured or reported when measured, and in many cases very few experimental data exist from which to draw conclusions. Therefore, further study of how environmental parameters affect eDNA state conversion and eDNA decay in aquatic environments is needed. We recommend analytic controls that can be used during the processing of water to assess potential losses of different eDNA states if all were present in a water sample, and we outline future experimental work that would help determine the dominant eDNA states in water.

Clays as Vehicles for Drug Photostability

Clay minerals are often used due to their high adsorption capacity, which has sparked interest in their biological applications to stabilize drugs and pharmaceutical products. This research aims to summarize information about the stability of drugs, cosmetics, dermocosmetics, and pharmaceutical compounds incorporated in the structure of different clay minerals. The databases used to search the articles were Web of Science, Scopus, PubMed, and Science Direct. Photostabilization of these compounds is reviewed and its importance demonstrated. For biological applications, the increase in solubility and bioavailability of clay minerals has proven useful for them as drug carriers. While their natural abundance, low toxicity, and accessible cost have contributed to classical applications of clay minerals, a wide range of interesting new applications may be facilitated, mainly through incorporating different organic molecules. The search for new functional materials is promising to challenge research on clay minerals in biological or biotechnological approaches.

Implications for mitigation of antibiotic resistance: Differential response of intracellular and extracellular antibiotic resistance genes to sludge fermentation coupled with thermal hydrolysis

Thermal hydrolysis pretreatment (THP) can effectively remove the antibiotic resistance genes (ARGs) from sewage sludge, but the rebounding effects in the subsequent anaerobic fermentation are often observed. The purpose of this study was to elucidate the distribution and fate of intracellular and extracellular ARGs (iARGs and eARGs) in the sludge acidogenic fermentation process coupled with THP. Our results revealed that THP significantly reduced the absolute abundance of total ARGs in raw sludge but increased eARGs by 0.3-1.4 log units under practical conditions (140 °C for 30 min). There is no significant difference in the removal of total ARGs between the two acidogenic fermenters receiving raw and hydrolyzed sludge, with iARGs prevailing in the produced biosolids. The succession of bacterial community and the co-occurrence relationships among ARG type, mobile genetic elements and bacterial taxa were observed, suggesting a phylogenetic basis for the iARGs patterns in fermented sludge. However, eARGs were susceptible to biodegradation with a half-life of 2.34 h and they contributed limitedly to the ARGs propagation through transformation. These findings suggest an emphasis on the mitigation of iARGs during the acidogenic fermentation of sludge, which would be achieved by lowering the richness and physicochemical destruction of potential hosts.

Montmorillonite with essential oils as antimicrobial agents, packaging, repellents, and insecticides: an overview

Essential oils (EOs) are complex natural mixtures of secondary plant metabolites that function as biocides and therapeutic agents. They are extensively used in bactericidal, virucidal, fungicidal, antiparasitic, insecticidal, pharmaceutical, and cosmetic products. However, certain characteristics, such as the volatility of EOs, hinder their widespread use. To mitigate this limitation, several studies have investigated combinations of EOs with natural materials, including clay minerals. Clay minerals are abundant in nature, biocompatible, and non-toxic to the environment and humans. Clay minerals such as montmorillonite possess available sites where EO molecules can interact. The combination of EOs with clay minerals produces new materials for various applications including antibacterial, antifungal, insecticidal/repellent, and active packaging materials. Therefore, this review focuses on the immobilization of several types of EOs in raw and modified montmorillonites. The applications of the described systems were evaluated and demonstrated the synergism of the properties of the isolated components as a function of different EOs incorporated in the silicate matrix.

A Critical Review on the Multiple Roles of Manganese in Stabilizing and Destabilizing Soil Organic Matter

Manganese (Mn) is a biologically important and redox-active metal that may exert a poorly recognized control on carbon (C) cycling in terrestrial ecosystems. Manganese influences ecosystem C dynamics by mediating biochemical pathways that include photosynthesis, serving as a reactive intermediate in the breakdown of organic molecules, and binding and/or oxidizing organic molecules through organo-mineral associations. However, the potential for Mn to influence ecosystem C storage remains unresolved. Although substantial research has demonstrated the ability of Fe- and Al-oxides to stabilize organic matter, there is a scarcity of similar information regarding Mn-oxides. Furthermore, Mn-mediated reactions regulate important litter decomposition pathways, but these processes are poorly constrained across diverse ecosystems. Here, we discuss the ecological roles of Mn in terrestrial environments and synthesize existing knowledge on the multiple pathways by which biogeochemical Mn and C cycling intersect. We demonstrate that Mn has a high potential to degrade organic molecules through abiotic and microbially mediated oxidation and to stabilize organic molecules, at least temporarily, through organo-mineral associations. We outline research priorities needed to advance understanding of Mn-C interactions, highlighting knowledge gaps that may address key uncertainties in soil C predictions.

Low mobility of CuO and TiO2 nanoparticles in agricultural soils of contrasting texture and organic matter content

The fate of nanoparticles (NPs) in soil under relevant environmental conditions is still poorly understood. In this study, the mobility of two metal-oxide nanoparticles (CuO and TiO₂) in contrasting agricultural soils was investigated in water-saturated soil columns. The transport of TiO₂ and CuO-NPs were assessed in six soils with three different textures (from sand to clay) and two contrasted organic matter (OM) contents for each texture. TiO₂ mobility was very low in all soils, regardless of texture and OM content. Mass recoveries were always less than 5%, probably in relation with the strong homo-aggregation of TiO₂-NPs observed in all soil solutions, with apparent sizes 3-6 times larger than their nominal size. This low mobility suggests that TiO₂-NPs present a low risk of direct groundwater contamination in contrasted surface soils. Although their retention was also generally high (more than 86%), CuO nanoparticles were found to be mobile in all soils. This is probably related to their smaller apparent size and low capacity of homo-aggregation of CuO-NPs in all soil solutions. No clear influence of neither soil texture or soil total organic matter content could be observed on CuO transport. However, this study shows that in contrasted agricultural soils, CuO-NPs transport is mainly controlled by the solutes dissolved in soil solution (DOC and PO₄ species), rather than by the properties of the soil solid phase.

New insights into the different adsorption kinetics of gallic acid and tannic acid on minerals via 1H NMR relaxation of bound water

The slower adsorption of lower molecular weight organic molecules remains poorly understood. This study investigated the adsorption kinetics of gallic acid (GA) and tannic acid (TA) on kaolinite (Kao), montmorillonite (Mon) and hematite (Hem), with an emphasis on the role of the bound water on the minerals. The lower adsorption of TA and GA on Kao than on Mon attributed to the lower specific surface area of Kao. Because of the electrostatic attraction, the adsorption of TA and GA on Hem was higher than that on Mon, even the specific surface area of the former was much lower than that of the later. The adsorption rates of TA on the three minerals were generally two orders of magnitude higher than those of GA. The adsorption kinetics of GA was strongly diffusion dependent; however, the diffusion process had limited influence on TA adsorption kinetics. The decreased c values of the intraparticle diffusion model of GA with increasing ionic strength provided additional direct evidence for the diffusion-dependent adsorption and the reduced hindrance by bound water via hydration layer compression. However, hydration layer compression had no effect on TA adsorption kinetics. The reduced ¹H NMR relaxation rate of bound water indicated that the bound water quantity on minerals decreased with increasing ionic strength, which proved the occurrence of hydration layer compression. This study highlighted the importance of bound water and the relative sizes of organic molecules in the adsorption kinetics of organic compounds on minerals, which should be carefully considered for their environmental fate studies.

Adsorption of double-stranded ribonucleic acids (dsRNA) to iron (oxyhydr-)oxide surfaces: comparative analysis of model dsRNA molecules and deoxyribonucleic acids (DNA)

Double-stranded ribonucleic acid (dsRNA) molecules are novel plant-incorporated protectants expressed in genetically modified RNA interference (RNAi) crops. Ecological risk assessment (ERA) of RNAi crops requires a heretofore-missing detailed understanding of dsRNA adsorption in soils, a key fate process. Herein, we systematically study the adsorption of a model dsRNA molecule and of two double-stranded deoxyribonucleic acid (DNA) molecules of varying lengths to three soil iron (oxyhydr-)oxides - goethite, lepidocrocite, and hematite - over a range of solution pH (4.5-10), ionic strength (I = 10-100 mM NaCl) and composition (0.5, 1, and 3 mM MgCl2) and in the absence and presence of phosphate (0.05-5 mM) as co-adsorbate. We hypothesized comparable adsorption characteristics of dsRNA and DNA based on their structural similarities. Consistently, the three nucleic acids (NAs) showed high adsorption affinities to the iron (oxyhydr-)oxides with decreasing adsorption in the order goethite, lepidocrocite, and hematite, likely reflecting a decrease in the hydroxyl group density and positive charges of the oxide surfaces in the same order. NA adsorption also decreased with increasing solution pH, consistent with weakening of NA electrostatic attraction to and inner-sphere complex formation with the iron (oxyhydr-)oxides surfaces as pH increased. Adsorbed NA concentrations increased with increasing I and in the presence of Mg2+, consistent with adsorbed NA molecules adopting more compact conformations. Strong NA-phosphate adsorption competition demonstrates that co-adsorbates need consideration in assessing dsRNA fate in soils. Comparable adsorption characteristics of dsRNA and DNA molecules to iron (oxyhydr-)oxides imply that information on DNA adsorption to soil particle surfaces can inform dsRNA ERA.

Towards the Optimization of eDNA/eRNA Sampling Technologies for Marine Biosecurity Surveillance

The field of eDNA is growing exponentially in response to the need for detecting rare and invasive species for management and conservation decisions. Developing technologies and standard protocols within the biosecurity sector must address myriad challenges associated with marine environments, including salinity, temperature, advective and deposition processes, hydrochemistry and pH, and contaminating agents. These approaches must also provide a robust framework that meets the need for biosecurity management decisions regarding threats to human health, environmental resources, and economic interests, especially in areas with limited clean-laboratory resources and experienced personnel. This contribution aims to facilitate dialogue and innovation within this sector by reviewing current approaches for sample collection, post-sampling capture and concentration of eDNA, preservation, and extraction, all through a biosecurity monitoring lens.

Interactions of extracellular DNA with aromatized biochar and protection against degradation by DNase I

With increasing environmental application, biochar (BC) will inevitably interact with and impact environmental behaviors of widely distributed extracellular DNA (eDNA), which however still remains to be studied. Herein, the adsorption/desorption and the degradation by nucleases of eDNA on three aromatized BCs pyrolyzed at 700 °C were firstly investigated. The results show that the eDNA was irreversibly adsorbed by aromatized BCs and the pseudo-second-order and Freundlich models accurately described the adsorption process. Increasing solution ionic strength or decreasing pH below 5.0 significantly increased the eDNA adsorption on BCs. However, increasing pH from 5.0 to 10.0 faintly decreased eDNA adsorption. Electrostatic interaction, Ca ion bridge interaction, and π-π interaction between eDNA and BC could dominate the eDNA adsorption, while ligand exchange and hydrophobic interactions were minor contributors. The presence of BCs provided a certain protection to eDNA against degradation by DNase I. BC-bound eDNA could be partly degraded by nuclease, while BC-bound nuclease completely lost its degradability. These findings are of fundamental significance for the potential application of biochar in eDNA dissemination management and evaluating the environmental fate of eDNA.

Polyvalent Metal Ion Promoted Adsorption of DNA Oligonucleotides by Montmorillonite

Montmorillonite (MMT) is a two-dimensional (2D) clay material. Its abundance on the early earth has attracted studies for its role in prebiotic reactions, and adsorption of DNA to MMT is potentially important for understanding the origin of life. Although several possible models of DNA adsorption on MMT have been established, a consensus on the adsorption mechanism has yet to be formed, thereby a fundamental adsorption study is performed here. Adding up to 300 mM NaCl failed to promote DNA adsorption on MMT, Al₂O₃, or SiO₂ nanoparticles. For polyvalent metals, DNA adsorption was achieved following the order Ce³⁺ > Cu²⁺ > Ni²⁺ > Zn²⁺. Among them, Ce³⁺ and Cu²⁺ inverted the surface charge of MMT to positive. In addition, using washing experiments, Cu²⁺- and Ce³⁺-mediated adsorption mainly depended on the DNA phosphate backbone, while Ni²⁺ and Zn²⁺ interacted with the backbone phosphate groups and adenine bases of DNA. Overall, these polyvalent metal ions promoted DNA adsorption via a cation bridge model. This research provides new insights into the surface interactions of MMT and DNA, which is conducive to future work on the interaction between clays and biopolymers.

Facile synthesis of polyoxometalate-modified metal organic frameworks for eliminating tetrabromobisphenol-A from water

Removal of tetrabromobisphenol-A (TBBPA) from wastewater is of significance to protect the aquatic life. The present study reports the facile preparation of polyoxometalate-modified metal-organic framework (MOFs) materials for TBBPA removal from water. The polyoxometalate-modified MOFs exhibited significantly higher affinity towards TBBPA than the control MOFs. The experimental data were fitted with the Langmuir, Freundlich and Dubinin-Radushkevich models. The TBBPA adsorption onto modified MOFs fitted the pseudo-second-order kinetic model. The equilibrium adsorption isotherms showed that the adsorption of TBBPA can be fitted by the Langmuir model. The maximum adsorption capacity of adsorbent composites reached 3.65 mg/g, with 95 % removal of TBBPA. The thermodynamic parameters indicated that adsorption was spontaneous. A blue shift of phosphorus peaks obtained from XPS spectra implied the formation of intrinsic chemical bonding between TBBPA and MOFs composites. Moreover, response surface methodology was employed to characterize the TBBPA adsorption in the co-existence of different factors. BPA had strong competition for TBBPA adsorption in a wide range of pH, but not at the middle level of Ca²⁺ concentration. Polyoxometalate-modified MOFs can easily be recycled using a simple organic solvent washing. This study provides a novel strategy for developing cost effective adsorbents to remove TBBPA from contaminated water.

Struvite crystallization induced the discrepant transports of antibiotics and antibiotic resistance genes in phosphorus recovery from swine wastewater

Struvite (MgNH₄PO₃·6H₂O) crystallization is one of important methods of phosphorus recovery from wastewater. As to livestock wastewater, the high-strength occurrence of antibiotics and antibiotic resistance genes might induce struvite recovery to spread antibiotic resistance to the environment. However, limited information has been reported on the simultaneous transport of antibiotics and ARGs in struvite recovery. In the present study, tetracyclines (TCs) and tetracyclines antibiotic resistance genes (ARGs) were selected as the targeted pollutants, and their discrepant residues in struvite recovery from swine wastewater were investigated. TCs and ARGs were obviously detected, with their contents of 4.88-79.5 mg/kg and 6.99 × 10⁷-2.14 × 10¹¹ copies/g, notably higher than those of TCs 0.550-1.94 mg/kg and ARGs 3.98 × 10⁴-5.66 × 10⁷ copies/g obtained from synthetic wastewater. The correlational relationship revealed that predominant factors affecting TCs and ARGs transports were different. Results from network analyses indicated that among the total edges, the negative correlations between TCs and ARGs predominately occupied 18.0%. The redundancy analysis revealed that mineral components in the recovered products, including struvite, K-struvite and amorphous calcium phosphate, coupling with organic contents, displayed insignificant roles on TCs residues, where heavy metals exerted positive and remarkable functions to boost TCs migration. Unexpectedly, mineral components and heavy metals did not displayed significant promotion on ARGs transport as a whole.

Facile Fabrication of Natural Polyelectrolyte-Nanoclay Composites: Halloysite Nanotubes, Nucleotides and DNA Study

Complexation of biopolymers with halloysite nanotubes (HNTs) can greatly affect their applicability as materials building blocks. Here we have performed a systematic investigation of fabrication of halloysite nanotubes complexes with nucleotides and genomic DNA. The binding of DNA and various nucleotide species (polyAU, UMP Na₂, ADP Na₃, dATP Na, AMP, uridine, ATP Mg) by halloysite nanotubes was tested using UV-spectroscopy. The study revealed that binding of different nucleotides to the nanoclay varied but was low both in the presence and absence of MgCl₂, while MgCl₂ facilitated significantly the binding of longer molecules such as DNA and polyAU. Modification of the nanotubes with DNA and nucleotide species was further confirmed by measurements of ζ-potentials. DNA-Mg-modified nanotubes were characterized using transmission electron (TEM), atomic force (AFM) and hyperspectral microscopies. Thermogravimetric analysis corroborated the sorption of DNA by the nanotubes, and the presence of DNA on the nanotube surface was indicated by changes in the surface adhesion force measured by AFM. DNA bound by halloysite in the presence of MgCl₂ could be partially released after addition of phosphate buffered saline. DNA binding and release from halloysite nanotubes was tested in the range of MgCl₂ concentrations (10–100 mM). Even low MgCl₂ concentrations significantly increased DNA sorption to halloysite, and the binding was leveled off at about 60 mM. DNA-Mg-modified halloysite nanotubes were used for obtaining a regular pattern on a glass surface by evaporation induced self-assembly process. The obtained spiral-like pattern was highly stable and resisted dissolution after water addition. Our results encompassing modification of non-toxic clay nanotubes with a natural polyanion DNA will find applications for construction of gene delivery vehicles and for halloysite self-assembly on various surfaces (such as skin or hair).