Soil microbiome feedbacks during disturbance-driven forest ecosystem conversion.

Disturbances cause rapid changes to forests, with different disturbance types and severities creating unique ecosystem trajectories that can impact the underlying soil microbiome. Pile burning-the combustion of logging residue on the forest floor-is a common fuel reduction practice that can have impacts on forest soils analogous to those following high-severity wildfire. Further, pile burning following clear-cut harvesting can create persistent openings dominated by nonwoody plants surrounded by dense regenerating conifer forest. A paired 60-year chronosequence of burn scar openings and surrounding regenerating forest after clear-cut harvesting provides a unique opportunity to assess whether belowground microbial processes mirror aboveground vegetation during disturbance-induced ecosystem shifts. Soil ectomycorrhizal fungal diversity was reduced the first decade after pile burning, which could explain poor tree seedling establishment and subsequent persistence of herbaceous species within the openings. Fine-scale changes in the soil microbiome mirrored aboveground shifts in vegetation, with short-term changes to microbial carbon cycling functions resembling a postfire microbiome (e.g. enrichment of aromatic degradation genes) and respiration in burn scars decoupled from substrate quantity and quality. Broadly, however, soil microbiome composition and function within burn scar soils converged with that of the surrounding regenerating forest six decades after the disturbances, indicating potential microbial resilience that was disconnected from aboveground vegetation shifts. This work begins to unravel the belowground microbial processes that underlie disturbance-induced ecosystem changes, which are increasing in frequency tied to climate change.

Fire Impacts on the Soil Metabolome and Organic Matter Biodegradability.

Global wildfire activity has increased since the 1970s and is projected to intensify throughout the 21st century. Wildfires change the composition and biodegradability of soil organic matter (SOM) which contains nutrients that fuel microbial metabolism. Though persistent forms of SOM often increase postfire, the response of more biodegradable SOM remains unclear. Here we simulated severe wildfires through a controlled "pyrocosm" approach to identify biodegradable sources of SOM and characterize the soil metabolome immediately postfire. Using microbial amplicon (16S/ITS) sequencing and gas chromatography-mass spectrometry, heterotrophic microbes (Actinobacteria, Firmicutes, and Protobacteria) and specific metabolites (glycine, protocatechuate, citric cycle intermediates) were enriched in burned soils, indicating that burned soils contain a variety of substrates that support microbial metabolism. Molecular formulas assigned by 21 T Fourier transform ion cyclotron resonance mass spectrometry showed that SOM in burned soil was lower in molecular weight and featured 20 to 43% more nitrogen-containing molecular formulas than unburned soil. We also measured higher water extractable organic carbon concentrations and higher CO2 efflux in burned soils. The observed enrichment of biodegradable SOM and microbial heterotrophs demonstrates the resilience of these soils to severe burning, providing important implications for postfire soil microbial and plant recolonization and ecosystem recovery.

Determination of Soil Contamination at the Wildland-Urban Interface after the 2021 Marshall Fire in Colorado, USA.

Wildfires at the wildland-urban interface (WUI) are increasingly common. The impacts of such events are likely distinct from those that occur strictly in wildland areas, as we would expect an elevated likelihood of soil contamination due to the combustion of anthropogenic materials. We evaluated the impacts of a wildfire at the WUI on soil contamination, sampling soils from residential and nonresidential areas located inside and outside the perimeter of the 2021 Marshall Fire in Colorado, USA. We found that fire-affected residential properties had elevated concentrations of some heavy metals (including Zn, Cu, Cr, and Pb), but the concentrations were still below levels of likely concern, and we observed no corresponding increases in concentrations of polycyclic aromatic hydrocarbons (PAHs). The postfire increases in metal concentrations were not generally observed in the nonresidential soils, highlighting the importance of combustion of anthropogenic materials for potential soil contamination from wildfires at the WUI. While soil contamination from the 2021 Marshall Fire was lower than expected, and likely below the threshold of concern for human health, our study highlights some of the challenges that need to be considered when assessing soil contamination after such fires.

Water monitoring with an automated smart sensor supported with solar power for real-time and long range detection of ferrous iron.

Low-power and smart sensing systems for iron detection are necessary for in situ monitoring of water quality. Here, a potentiometric Fe2+-selective electrode (ISE) was fabricated based on cyanomethyl N-methyl-N-phenyl dithiocarbamate for the first time as an ionophore. Under optimal conditions, the ISE showed a Nernstian slope of 29.76 ± 0.6 mV per decade for Fe2+ ions over a wide concentration range from 1.0 × 10-1 to 1.0 × 10-5 M with a lower detection limit (LOD) of 1.0 × 10-6 M. The ISE interference of various cations on the potentiometric response was also investigated. The ISE had a response time less than 3 s and the lifetime was two months. Also, an automated, long-range (LoRa), wireless enabled sampling microfluidic device powered with a solar panel as an autonomous power source was developed for a continuous sampling and sensing process. The sensing platform was employed in the determination of Fe2+ in acid mine drainage and spiked water samples with an average recovery of 100.7%. This simple, inexpensive (below $350), portable sensing platform will allow for rapid real-time monitoring of ground-, drinking-, and industrial waters contaminated with iron.

Multitask Deep Learning Enabling a Synergy for Cadmium and Methane Mitigation with Biochar Amendments in Paddy Soils.

Biochar has demonstrated significant promise in addressing heavy metal contamination and methane (CH4) emissions in paddy soils; however, achieving a synergy between these two goals is challenging due to various variables, including the characteristics of biochar and soil properties that influence biochar's performance. Here, we successfully developed an interpretable multitask deep learning (MTDL) model by employing a tensor tracking paradigm to facilitate parameter sharing between two separate data sets, enabling a synergy between Cd and CH4 mitigation with biochar amendments. The characteristics of biochar contribute similar weightings of 67.9% and 62.5% to Cd and CH4 mitigation, respectively, but their relative importance in determining biochar's performance varies significantly. Notably, this MTDL model excels in custom-tailoring biochar to synergistically mitigate Cd and CH4 in paddy soils across a wide geographic range, surpassing traditional machine learning models. Our findings deepen our understanding of the interactive effects of Cd and CH4 mitigation with biochar amendments in paddy soils, and they also potentially extend the application of artificial intelligence in sustainable environmental remediation, especially when dealing with multiple objectives.

Molecular insights into the bonding mechanisms between selenium and dissolved organic matter.

Natural organic matter (NOM) plays a critical role in the mobilization and bioavailability of metals and metalloids in the aquatic environment. Selenium (Se), an environmental contaminant of aquatic systems, has drawn increasing attention over the years. While Se is a vital micronutrient to human beings, animals and plants, excess Se intake may pose serious long-term risks. However, the interaction between Se and dissolved organic matter (DOM) remains relatively unexplored, especially the reaction mechanisms and interactions of specific NOM components of certain molecular weight and the corresponding functional group change. Herein, we report an investigation on the interactions between Se and DOM by focusing on the mass distribution profile change of operationally defined molecular weight fractions of humic acid (HA) and fulvic acid (FA). The results showed that across all molecular weights studied, HA fractions were more prone to enhanced aggregation upon introduction of Se into the system. For FA, the presence of Se species results in aggregation, dissociation, and redox reactions with the first two being the major mechanisms. Total organic carbon analysis (TOC), UV-vis spectroscopy (UV-vis), and Orbitrap MS data showed that [10, 30] kDa MW fraction had the largest aromatic decrease (CRAM-like, lignin-like and tannin-like) upon addition of SeO2 via dissociation as the dominant mechanism. Fourier transform infrared spectroscopy (FT-IR) revealed that Se based bridging or chelation of functional groups from individual DOM components through hydrogen bonding in the form of SeO⋯H and possibly Se⋯H and/or attractive electrostatic interactions lead to aggregated DOM1⋯Se⋯DOM2. It was concluded from two-dimensional correlation analyses of excitation emission matrix (EEM) and FT-IR that the preferred Se-binding follows lipid âž” peptide âž” tannin âž” aromatic functionalities. These results provide new understanding of Se interactions with various NOM components in aquatic environments and provide insight for Se assessing health risk and/or treatment of Se contaminated water.

Agricultural Sulfur Applications Alter the Quantity and Composition of Dissolved Organic Matter from Field-to-Watershed Scales.

Over the past several decades, agricultural sulfur (S) use has dramatically increased. Excess S in the environment can cause several biogeochemical and ecologic consequences, including methylmercury production. This study investigated agriculturally associated changes to organic S─the most dominant form of S within soils─from field-to-watershed scales. Using a novel complementary suite of analytical methods, we combined Fourier transform ion cyclotron resonance mass spectrometry, δ34S-DOS, and S X-ray absorption spectroscopy to characterize dissolved organic S (DOS) in soil porewater and surface water samples from vineyard agriculture (S addition) and forest/grassland areas (no S addition) within the Napa River watershed (California, U.S.). Vineyard soil porewater dissolved organic matter samples had two-fold higher S content compared to forest/grasslands and had unique CHOS2 chemical formulas─the latter also found in tributary and Napa River surface water. The isotopic difference between δ34S-DOS and δ34S-SO42- values provided insights into the likely dominant microbial S processes by land use/land cover (LULC), whereas the S oxidation state did not strongly differ by LULC. The results add to our understanding of the modern S cycle and point to upland agricultural areas as S sources with the potential for rapid S transformations in downgradient environments.

Persisting Effects in Daphnia magna Following an Acute Exposure to Flowback and Produced Waters from the Montney Formation.

Hydraulic fracturing extracts oil and gas through the injection of water and proppants into subterranean formations. These injected fluids mix with the host rock formation and return to the surface as a complex wastewater containing salts, metals, and organic compounds, termed flowback and produced water (FPW). Previous research indicates that FPW is toxic to Daphnia magna (D. magna), impairing reproduction, molting, and maturation time; however, recovery from FPW has not been extensively studied. Species unable to recover have drastic impacts on populations on the ecological scale; thus, this study sought to understand if recovery from an acute 48 h FPW exposure was possible in the freshwater invertebrate, D. magna by using a combination of physiological and molecular analyses. FPW (0.75%) reduced reproduction by 30% and survivorship to 32% compared to controls. System-level quantitative proteomic analyses demonstrate extensive perturbation of metabolism and protein transport in both 0.25 and 0.75% FPW treatments after a 48 h FPW exposure. Collectively, our data indicate that D. magna are unable to recover from acute 48 h exposures to ≥0.25% FPW, as evidence of toxicity persists for at least 19 days post-exposure. This study highlights the importance of considering persisting effects following FPW remediation when modeling potential spill scenarios.

Iron Vacancy Accelerates Fe(II)-Induced Anoxic As(III) Oxidation Coupled to Iron Reduction.

Chemical oxidation of As(III) by iron (Fe) oxyhydroxides has been proposed to occur under anoxic conditions and may play an important role in stabilization and detoxification of As in subsurface environments. However, this reaction remains controversial due to lack of direct evidence and poorly understood mechanisms. In this study, we show that As(III) oxidation can be facilitated by Fe oxyhydroxides (i.e., goethite) under anoxic conditions coupled with the reduction of structural Fe(III). An excellent electron balance between As(V) production and Fe(III) reduction is obtained. The formation of an active metastable Fe(III) phase at the defective surface of goethite due to atom exchange is responsible for the oxidation of As(III). Furthermore, the presence of defects (i.e., Fe vacancies) in goethite can noticeably enhance the electron transfer (ET) and atom exchange between the surface-bound Fe(II) and the structural Fe(III) resulting in a two time increase in As(III) oxidation. Atom exchange-induced regeneration of active goethite sites is likely to facilitate As(III) coordination and ET with structural Fe(III) based on electrochemical analysis and theoretical calculations showing that this reaction pathway is thermodynamically and kinetically favorable. Our findings highlight the synergetic effects of defects in the Fe crystal structure and Fe(II)-induced catalytic processes on anoxic As(III) oxidation, shedding a new light on As risk management in soils and subsurface environments.

Incorporation of Cu into Goethite Stimulates Oxygen Activation by Surface-Bound Fe(II) for Enhanced As(III) Oxidative Transformation.

The dark production of reactive oxygen species (ROS) coupled to biogeochemical cycling of iron (Fe) plays a pivotal role in controlling arsenic transformation and detoxification. However, the effect of secondary atom incorporation into Fe(III) oxyhydroxides on this process is poorly understood. Here, we show that the presence of oxygen vacancy (OV) as a result of Cu incorporation in goethite substantially enhances the As(III) oxidation by Fe(II) under oxic conditions. Electrochemical and density functional theory (DFT) evidence reveals that the electron transfer (ET) rate constant is enhanced from 0.023 to 0.197 s-1, improving the electron efficiency of the surface-bound Fe(II) on OV defective surfaces. The cascade charge transfer from the surface-bound Fe(II) to O2 mediated by Fe(III) oxyhydroxides leads to the O-O bond of O2 stretching to 1.46-1.48 Šequivalent to that of superoxide (•O2-), and •O2- is the predominant ROS responsible for As(III) oxidation. Our findings highlight the significant role of atom incorporation in changing the ET process on Fe(III) oxyhydroxides for ROS production. Thus, such an effect must be considered when evaluating Fe mineral reactivity toward changing their surface chemistry, such as those noted here for Cu incorporation, which likely determines the fates of arsenic and other redox sensitive pollutants in the environments with oscillating redox conditions.

Interactions between Extracellular DNA and Perfluoroalkyl Acids (PFAAs) Decrease the Bioavailability of PFAAs in Pakchoi (Brassica chinensis L.).

Perfluoroalkyl acids (PFAAs) are emerging ionic organic pollutants worldwide. Great amounts of extracellular DNA (∼mg/kg) coexist with PFAAs in the environment. However, PFAA-DNA interactions and effects of such interactions have not been well studied. Herein, we used isothermal titration calorimetry (ITC), spectroscopy, and computational simulations to investigate the PFAA-DNA interactions. ITC assays showed that specific binding affinities of PFHxA-DNA, PFOA-DNA, PFNA-DNA, and PFOS-DNA were 5.14 × 105, 3.29 × 105, 1.99 × 105, and 2.18 × 104 L/mol, respectively, which were about 1-2 orders of magnitude stronger than those of PFAAs with human serum albumin. Spectral analysis suggested interactions of PFAAs with adenine (A), cytosine (C), guanine (G), and thymine (T), among which grooves associated with thymine were the major binding sites. Molecular dynamics simulations and quantum chemical calculations suggested that hydrogen bonds and van der Waals forces were the main interaction forces. Such a PFAA-DNA binding decreased the bioavailability of PFAAs in plant seedlings. The findings will help to improve the current understanding of the interaction between PFAAs and biomacromolecules, as well as how such interactions affect the bioavailability of PFAAs.

Improved Dynamic Range, Resolving Power, and Sensitivity Achievable with FT-ICR Mass Spectrometry at 21 T Reveals the Hidden Complexity of Natural Organic Matter.

Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR MS) is the only mass analyzer that can resolve the molecular complexity of natural organic matter at the level of elemental composition assignment. Here, we leverage the high dynamic range, resolving power, resistance to peak coalescence, and maximum ion number and ion trapping duration in a custom built, 21 tesla hybrid linear ion trap /FT-ICR mass spectrometer for a dissolved organic matter standard (Suwanne River Fulvic Acid). We compare the effect of peak-picking threshold (3σ, 4σ, 5σ, and 6σ) on number of elemental composition assignments, mass measurement accuracy, and dynamic range for a 6.3 s transient across the mass range of m/z 200-1200 that comprises the highest achieved resolving power broadband FT-ICR mass spectrum collected to date. More than 36 000 species are assigned with signal magnitude greater than 3σ at root-mean-square mass error of 36 ppb, the most species identified reported to date for dissolved organic matter. We identify 18O and 17O isotopologues and resolve isobaric overlaps on the order of a few electrons across a wide mass range (up to m/z 1000) leveraging mass resolving powers (3 000 000 at m/z 200) only achievable by 21 T FT-ICR MS and increased by ∼30% through absorption mode data processing. Elemental compositions unique to the 3σ span a wide compositional range of aromaticity not detected at higher peak-picking thresholds. Furthermore, we leverage the high dynamic range at 21 T FT-ICR MS to provide a molecular catalogue of a widely utilized reference standard (SRFA) to the analytical community collected on the highest performing mass analyzer for complex mixture analysis to date. This instrument is available free of charge to scientists worldwide.

Wildfire-dependent changes in soil microbiome diversity and function.

Forest soil microbiomes have crucial roles in carbon storage, biogeochemical cycling and rhizosphere processes. Wildfire season length, and the frequency and size of severe fires have increased owing to climate change. Fires affect ecosystem recovery and modify soil microbiomes and microbially mediated biogeochemical processes. To study wildfire-dependent changes in soil microbiomes, we characterized functional shifts in the soil microbiota (bacteria, fungi and viruses) across burn severity gradients (low, moderate and high severity) 1 yr post fire in coniferous forests in Colorado and Wyoming, USA. We found severity-dependent increases of Actinobacteria encoding genes for heat resistance, fast growth, and pyrogenic carbon utilization that might enhance post-fire survival. We report that increased burn severity led to the loss of ectomycorrhizal fungi and less tolerant microbial taxa. Viruses remained active in post-fire soils and probably influenced carbon cycling and biogeochemistry via turnover of biomass and ecosystem-relevant auxiliary metabolic genes. Our genome-resolved analyses link post-fire soil microbial taxonomy to functions and reveal the complexity of post-fire soil microbiome activity.

Impact of beaver ponds on biogeochemistry of organic carbon and nitrogen along a fire-impacted stream.

Wildfires, which are increasing in frequency and severity in the western U.S., impact water quality through increases in erosion, and transport of nutrients and metals. Meanwhile, beaver populations have been increasing since the early 1900s, and the ponds they create slow or impound hydrologic and elemental fluxes, increase soil saturation, and have a high potential to transform redox active elements (e.g., oxygen, nitrogen, sulfur, and metals). However, it remains unknown how the presence of beaver ponds in burned watersheds may impact retention and transformation of chemical constituents originating in burned uplands (e.g., pyrogenic dissolved organic matter; pyDOM) and the consequences for downstream water quality. Here, we investigate the impact of beaver ponds on the chemical properties and molecular composition of dissolved forms of C and N, and the microbial functional potential encoded within these environments. The chemistry and microbiology of surface water and sediment changed along a stream sequence starting upstream of fire and flowing through multiple beaver ponds and interconnecting stream reaches within a burned high-elevation forest watershed. The relative abundance of N-containing compounds increased in surface water of the burned beaver ponds, which corresponded to lower C/N and O/C, and higher aromaticity as characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The resident microbial communities lack the capacity to process such aromatic pyDOM, though genomic analyses demonstrate their potential to metabolize various compounds in the anaerobic sediments of the beaver ponds. Collectively, this work highlights the role of beaver ponds as biological "hotspots" with unique biogeochemistry in fire-impacted systems.

Nitrogen Enrichment during Soil Organic Matter Burning and Molecular Evidence of Maillard Reactions.

Wildfires in forested watersheds dramatically alter stored and labile soil organic matter (SOM) pools and the export of dissolved organic matter (DOM). Ecosystem recovery after wildfires depends on soil microbial communities and revegetation and therefore is limited by the availability of nutrients, such as nitrogen-containing and labile, water-soluble compounds. However, SOM byproducts produced at different wildfire intensities are poorly understood, leading to difficulties in assessing wildfire severity and predicting ecosystem recovery. In this work, water-extractable organic matter (WEOM) from laboratory microcosms of soil burned at discrete temperatures was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to study the impacts of fire temperature on SOM and DOM composition. The molecular composition derived from different burn temperatures indicated that nitrogen-containing byproducts were enriched with heating and composed of a wide range of aromatic features and oxidation states. Mass difference-based analysis also suggested that products formed during heating could be modeled using transformations along the Maillard reaction pathway. The enrichment of N-containing SOM and DOM at different soil burning intensities has important implications for ecosystem recovery and downstream water quality.

Enhanced Speciation of Pyrogenic Organic Matter from Wildfires Enabled by 21 T FT-ICR Mass Spectrometry.

Wildfires affect soils through the formation of pyrogenic organic matter (pyOM) (e.g., char and soot). While many studies examine the connection between pyOM persistence and carbon (C) composition, nitrogen (N) transformation in wildfire-impacted systems remains poorly understood. Thermal reactions in wildfires transform biomass into a highly complex, polyfunctional, and polydisperse organic mixture that challenges most mass analyzers. High-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is the only mass analyzer that achieves resolving powers sufficient to separate species that differ in mass by the mass of an electron across a wide molecular weight range (m/z 150-1500). We report enhanced speciation of organic N by positive-ion electrospray ionization (ESI) that leverages ultrahigh resolving power (m/Δm50% = 1 800 000 at m/z 400) and mass accuracy (<10-100 ppb) achieved by FT-ICR MS at 21 T. Isobaric overlaps, roughly the mass of an electron (Me- = 548 µDa), are resolved across a wide molecular weight range and are more prevalent in positive ESI than negative ESI. The custom-built 21 T FT-ICR MS instrument identifies previously unresolved mass differences in CcHhNnOoSs formulas and assigns more than 30 000 peaks in a pyOM sample. This is the first molecular catalogue of pyOM by positive-ion ESI 21 T FT-ICR MS and presents a method to provide new insight into terrestrial cycling of organic carbon and nitrogen in wildfire impacted ecosystems.

PFAS Analysis with Ultrahigh Resolution 21T FT-ICR MS: Suspect and Nontargeted Screening with Unrivaled Mass Resolving Power and Accuracy.

Per- and polyfluoroalkyl substances (PFASs) are a large family of thousands of chemicals, many of which have been identified using nontargeted time-of-flight and Orbitrap mass spectrometry methods. Comprehensive characterization of complex PFAS mixtures is critical to assess their environmental transport, transformation, exposure, and uptake. Because 21 tesla (T) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers the highest available mass resolving power and sub-ppm mass errors across a wide molecular weight range, we developed a nontargeted 21 T FT-ICR MS method to screen for PFASs in an aqueous film-forming foam (AFFF) using suspect screening, a targeted formula database (C, H, Cl, F, N, O, P, S; ≤865 Da), isotopologues, and Kendrick-analogous mass difference networks (KAMDNs). False-positive PFAS identifications in a natural organic matter (NOM) sample, which served as the negative control, suggested that a minimum length of 3 should be imposed when annotating CF2-homologous series with positive mass defects. We putatively identified 163 known PFASs during suspect screening, as well as 134 novel PFASs during nontargeted screening, including a suspected polyethoxylated perfluoroalkane sulfonamide series. This study shows that 21 T FT-ICR MS analysis can provide unique insights into complex PFAS composition and expand our understanding of PFAS chemistries in impacted matrices.

High Spatial Resolution Fluorescence Imagery for Optimized Pest Management in a Huanglongbing-Infected Citrus Grove.

Huanglongbing (HLB), or citrus greening disease, has significantly decreased citrus production all over the world. The disease management currently depends on the efficient application and adequate distribution of insecticides to reduce the density of the disease vector, the Asian citrus psyllid. Here, we use a novel fluorescent-based method to evaluate insecticide distribution in an HLB-infected citrus grove in Florida. Specifically, we evaluated six different locations within citrus trees, the top and bottom sides of leaves, the effect of application approach (tractor versus airplane), and different application rates. We found that despite the insecticide distribution being highly variable among the different locations within a tree, the top of the leaves received an average increase of 21 times more than the bottom of the leaves. Application by tractor also resulted in a 4- to 87-fold increase in insecticide coverage compared with aerial application, depending on the location in the tree and side of the leaf. When taken to context with the type of insecticide that is applied (systemic vs. contact), these results can be used to optimize a pest management strategy to effectively target psyllids and other pests while minimizing the time and money spent on insecticide application and reducing risk to the environment.

Humidity induces the formation of radicals and enhances photodegradation of chlorinated-PAHs on Fe(III)-montmorillonite.

Chlorinated-PAHs (ClPAHs) are widely detected in the soil surface and atmospheric particles. However, the underlying mechanisms of their photodegradation are not well understood. In the present study, the formation of radicals on ClPAHs-contaminated clay minerals was quantitatively monitored via electron paramagnetic resonance (EPR) spectroscopy, and the impact of relative humidity (RH) was systematically explored. ClPAHs removal (> 75%) was attributed to electron transfer and •OH attack. The degradation easiness of ClPAHs follows: 2-ClNAP >2-ClANT >9-ClPHE >1-ClPYR. Light irradiation significantly improved the generation of reactive oxygen species (ROS, such as •OH and •O2-), and further generate a series of hydroxylated products of ClPAHs. Persistent free radicals (PFRs) were only detected on clay minerals contaminated with 2-ClANT and 1-ClPYR. RH 10-80%, the concentration of •OH and •O2- increased by 1.07 and 62.79 times respectively, which facilitated transformation of PFRs and ClPAHs degradation. The results of quantum chemical calculations indicate that the initial reaction of ClPAHs photodegradation is mediated by the substitution of •OH for chlorine groups. The present work implies that higher humidity may decrease the generation of PFRs on clay minerals and help mitigate the threats of PFRs and ClPAHs to human health.

Constructed wetlands for polishing oil and gas produced water releases.

Produced water (PW) is the largest waste stream associated with oil and gas (O&G) operations and contains petroleum hydrocarbons, heavy metals, salts, naturally occurring radioactive materials and any remaining chemical additives. In some areas in Wyoming, constructed wetlands (CWs) are used to polish PW downstream of National Pollutant Discharge Elimination System (NPDES) PW release points. In recent years, there has been increased interest in finding lower cost options, such as CWs, for PW treatment. The goal of this study was to understand the efficacy of removal and environmental fate of O&G organic chemical additives in CW systems used to treat PW released for agricultural beneficial reuse. To achieve this goal, we analyzed water and sediment samples for organic O&G chemical additives and conducted 16S rRNA gene sequencing for microbial community characterization on three such systems in Wyoming, USA. Three surfactants (polyethylene glycols, polypropylene glycols, and nonylphenol ethoxylates) and one biocide (alkyldimethylammonium chloride) were detected in all three PW discharges and >94% removal of all species from PW was achieved after treatment in two CWs in series. These O&G extraction additives were detected in all sediment samples collected downstream of PW discharges. Chemical and microbial analyses indicated that sorption and biodegradation were the main attenuation mechanisms for these species. Additionally, all three discharges showed a trend of increasingly diverse, but similar, microbial communities with greater distance from NPDES PW discharge points. Results of this study can be used to inform design and management of constructed wetlands for produced water treatment.