Abiotic Transformation Research Articles

Coupled Biotic-Abiotic Processes Control Biogeochemical Cycling of Dissolved Organic Matter in the Columbia River Hyporheic Zone

A critical component of assessing the impacts of climate change on watershed ecosystems involves understanding the role that dissolved organic matter (DOM) plays in driving whole ecosystem metabolism. The hyporheic zone—a biogeochemical control point where ground water and river water mix—is characterized by high DOM turnover and microbial activity and is responsible for a large fraction of lotic respiration. Yet, the dynamic nature of this ecotone provides a challenging but important environment to parse out different DOM influences on watershed function and net carbon and nutrient fluxes. We used high-resolution Fourier-transform ion cyclotron resonance mass spectrometry to provide a detailed molecular characterization of DOM and its transformation pathways in the Columbia river watershed. Samples were collected from ground water (adjacent unconfined aquifer underlying the Hanford 300 Area), Columbia river water, and its hyporheic zone. The hyporheic zone was sampled at five locations to capture spatial heterogeneity within the hyporheic zone. Our results revealed that abiotic transformation pathways (e.g., carboxylation), potentially driven by abiotic factors such as sunlight, in both the ground water and river water are likely influencing DOM availability to the hyporheic zone, which could then be coupled with biotic processes for enhanced microbial activity. The ground water profile revealed high rates of N and S transformations via abiotic reactions. The river profile showed enhanced abiotic photodegradation of lignin-like molecules that subsequently entered the hyporheic zone as low molecular weight, more degraded compounds. While the compounds in river water were in part bio-unavailable, some were further shown to increase rates of microbial respiration. Together, river water and ground water enhance microbial activity within the hyporheic zone, regardless of river stage, as shown by elevated putative amino-acid transformations and the abundance of amino-sugar and protein-like compounds. This enhanced microbial activity is further dependent on the composition of ground water and river water inputs. Our results further suggest that abiotic controls on DOM should be incorporated into predictive modeling for understanding watershed dynamics, especially as climate variability and land use could affect light exposure and changes to ground water essential elements, both shown to impact the Columbia river hyporheic zone.

Abiotic Transformation of Lamotrigine by Redox-Active Mineral and Phenolic Compounds

The anticonvulsant drug lamotrigine is a recalcitrant environmental pollutant. It was detected in drinking water, surface water, reclaimed wastewater, arable soils, and even in edible crops. In this work, we studied the mechanisms of lamotrigine transformation by a common redox soil mineral, birnessite, in a single-solute system and in bisolute systems with vanillic acid or o-methoxyphenol. In the single-solute system, 28% of lamotrigine was transformed and 14 transformation products (TPs) were identified. Based on a detailed analysis of the TPs, we suggested that lamotrigine is transformed mainly by oxidation, addition, and dechlorination reactions. In the bisolute systems, the redox-active phenolic compounds enhanced the elimination and transformation of lamotrigine. Vanillic acid was more efficient, generating 92% transformation of lamotrigine (58 TPs were identified), whereas o-methoxyphenol induced 48% transformation (35 TPs were identified). In the bisolute system with phenolic compounds, lamotrigine has possibly been transformed mainly via addition reactions with phenolic compounds and their oxidation products (protocatechuic acid, quinone, and oligomers). Thus, masses of the formed TPs were elevated as compared to the parent compound. The current study demonstrates the important role of redox-active minerals and naturally occurring phenolic compounds in abiotic removal and transformation of a recalcitrant environmental pollutant.

Combining In Silico Tools with Multicriteria Analysis for Alternatives Assessment of Hazardous Chemicals: Accounting for the Transformation Products of decaBDE and Its Alternatives

Transformation products ought to be an important consideration in chemical alternatives assessment. In this study, a recently established hazard ranking tool for alternatives assessment based on in silico data and multicriteria decision analysis (MCDA) methods was further developed to include chemical transformation products. Decabromodiphenyl ether (decaBDE) and five proposed alternatives were selected as case chemicals; biotic and abiotic transformation reactions were considered using five in silico tools. A workflow was developed to select transformation products with the highest occurrence potential. The most probable transformation products of the alternative chemicals were often similarly persistent but more mobile in aquatic environments, which implies an increasing exposure potential. When persistence (P), bioaccumulation (B), mobility in the aquatic environment (M), and toxicity (T) are considered (via PBT, PMT, or PBMT composite scoring), all six flame retardants have at least one transformation product that can be considered more hazardous, across diverse MCDA. Even when considering transformation products, the considered alternatives remain less hazardous than decaBDE, though the range of hazard of the five alternatives was reduced. The least hazardous of the considered alternatives were melamine and bis(2-ethylhexyl)-tetrabromophthalate. This developed tool could be integrated within holistic alternatives assessments considering use and life cycle impacts or additionally prioritizing transformation products within (bio)monitoring screening studies.

Chlorinated Ethene Degradation Rate Coefficients Simulated with Intact Sandstone Core Microcosms.

Abiotic transformation of trichloroethene (TCE) in fractured porous rock such as sandstone is challenging to characterize and quantify. The objective of this study was to estimate the pseudo first-order abiotic reaction rate coefficients in diffusion-dominated intact core microcosms. The microcosms imitated clean flow through a fracture next to a contaminated rock matrix by exchanging uncontaminated groundwater, unamended or lactate-amended, in a chamber above a TCE-infused sandstone core. Rate coefficients were assessed using a numerical model of the microcosms that were calibrated to monitoring data. Average initial rate coefficients for complete dechlorination of TCE to acetylene, ethene, and ethane were estimated as 0.019 y-1 in unamended microcosms and 0.024 y-1 in lactate-amended microcosms. Moderately higher values (0.026 y-1 for unamended and 0.035 y-1 for lactate-amended) were obtained based on 13C enrichment data. Abiotic transformation rate coefficients based on gas formation were decreased in unamended microcosms after ∼25 days, to an average of 0.0008 y-1. This was presumably due to depletion of reductive capacity (average values of 0.12 ± 0.10 μeeq/g iron and 18 ± 15 μeeq/g extractable iron). Model-derived rate coefficients and reductive capacities for the intact core microcosms aligned well with results from a previous microcosm study using crushed sandstone from the same site.

Impact of long-term irrigation with municipal reclaimed wastewater on the uptake and degradation of organic contaminants in lettuce and leek

A two years drip irrigation of lettuce and leek crops with treated municipal wastewater without and with spiking with fourteen wastewater relevant contaminants at 10 μg/L concentration level was conducted under greenhouse cultivation conditions to investigate their potential accumulation in soil and leaves and to assess human health related risks. Lettuce and leek crops were selected as a worse-case scenario since leafy green vegetable has a high potential for organic contaminants uptake. The results revealed limited accumulation of contaminants in soil and plant leaves, their concentration levels being in the range of 1–30 ng/g and 1–660 ng/g range in soil and leaves, respectively. This was likely related to abiotic and biotic transformation or simply binding processes in soil, which limited contaminants plant uptake. This assumption was underpinned by studies of the enantiomeric fractionation of chiral compounds (e.g. climbazole and metoprolol) in soil as pieces of evidence of biodegradation and by the identification of transformation products or metabolites in leaves by means of liquid chromatography - high resolution - mass spectrometry using a suspect screening workflow. The high bioconcentration factors were not limited to compounds with intermediate Dow (100 to 1000) such as carbamazepine but also observed for hydrophilic compounds such as clarithromycin, hydrochlorothiazide and the food additives acesulfame and sucralose. This result assumed that accumulation was not only driven by passive processes (e.g. lipoidal diffusion through lipid bilayer cell membranes or Casparian strip) but might be supported by carrier-mediated transporters. As a whole, this study confirmed earlier reports on the a de minimis human health risk related to the consumption of raw leafy green vegetable irrigated with domestic TWW containing organic contaminants residues.

Performance and potential mechanism of transformation of polycyclic aromatic hydrocarbons (PAHs) on various iron oxides

The abiotic transformation of polycyclic aromatic hydrocarbons (PAHs) is significantly impacted by soil components, especially inorganic redox species like iron oxides. In this study, the catalytic activities of three types of iron oxides in PAHs degradation without light irradiation were evaluated using a combination of experimental techniques. The results showed that α-Fe2O3 possessed the highest transformation rate for anthracene (ANT), with a reaction rate constant (Kobs) up to 0.28 d−1, followed by Fe3O4 (Kobs = 0.06 d−1) and α-FeOOH (Kobs = 0.06 d−1). X-ray photoelectron spectroscopy (XPS) characterization suggested that α-Fe2O3 had the highest oxygen vacancy concentration, which was conducive to the adsorption of O2 by α-Fe2O3, providing sufficient adsorbed oxygen species. Oxygen vacancy contributed to the exposure of Fe(III), and accordingly, more active sites were created that were responsible for ANT degradation. According to these results, two possible pathways for the degradation of PAHs on iron oxides can be concluded: (1) direct oxidation by Fe(III) and (2) oxidation by the O2•− generated onto oxygen vacancies. This study provides significant insights into the environmental fate of PAHs on iron oxides, and raises the possibility that iron oxides may be used as catalytic materials in the remediation PAHs-contaminated soil.

Two distinct Dehalobacter strains sequentially dechlorinate 1,1,1-trichloroethane and 1,1-dichloroethane at a field site treated with granular zero valent iron and guar gum

Chlorinated ethanes are environmental pollutants found frequently at many contaminated industrial sites. 1,1,1-Trichloroethane (1,1,1-TCA) can be dechlorinated and detoxified via abiotic transformation or biologically by the action of dechlorinating microorganisms such as Dehalobacter (Dhb). At a field site, it is challenging to distinguish abiotic vs. biotic mechanisms as both processes share common transformation products. In this study, we evaluated using the Dhb 16S rRNA gene and specific reductive dehalogenase genes as biomarkers for 1,1,1-TCA and 1,1-dichloroethane (1,1-DCA) dechlorination. We analyzed samples from laboratory groundwater microcosms and from an industrial site where a mixture of granular zero valent iron (ZVI) and guar gum was injected for 1,1,1-TCA remediation. Abiotic and biotic transformation products were monitored and the changes in dechlorinating organisms were tracked using quantitative PCR (qPCR) with primers targeting the Dhb 16S rRNA gene and two functional genes cfrA and dcrA encoding enzymes that dechlorinate 1,1,1-TCA to 1,1-DCA and 1,1-DCA to chloroethane (CA), respectively. The abundance of the cfrA- and dcrA-like genes confirmed that the two dechlorination steps were carried out by two distinct Dhb populations at the site. The biomarkers used in this study proved useful for monitoring different Dhb populations responsible for step-wise dechlorination and tracking biodegradation of 1,1,1-TCA and 1,1-DCA where both abiotic (e.g., with ZVI) and biotic processes co-occur.

Contrasting impacts of pH on the abiotic transformation of hydrochar-derived dissolved organic matter mediated by δ-MnO2

Hydrochar produced from hydrothermal carbonization of agricultural waste becomes a promising soil conditioner, and especially, its labile fraction, dissolved organic matter (DOM) may play an important role in improving soil fertility and quality. However, little is known about the interaction and transformation of hydrochar-derived DOM with soil reactive components after its amendment into soil. The abiotic transformation of hydrochar-derived DOM by a common soil metal oxide, δ-MnO2 at environmentally relevant pHs (4, 6 and 8) was investigated by using a combination of batch experiments and advanced spectroscopic techniques. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and fluorescence spectroscopy revealed that lignins and carboxyl-rich alicyclic molecules were predominant in hydrochar-derived DOM and phenolic fluorophores were the dominant fluorescent composition. In the presence of δ-MnO2, hydrochar-derived DOM was rapidly transformed via both decomposition and polycondensation, resulting in significant structure changes of hydrochar-derived DOM with increasing humic-like fraction similar to soil organic matter (SOM). The transformation process of hydrochar-derived DOM molecules was highly pH-dependent, with polycondensation occurring preferentially at pH 8 and more rapid oxidation at pH 4. Meanwhile, δ-MnO2 was reduced to Mn(II) and Mn(III) during the reaction, and the accumulation of Mn(III) in the solid phase of δ-MnO2 reached a maximum at pH 4. Collectively, the results characterized the transformation mechanism of DOM by δ-MnO2 at molecular level, which provided a new perspective for better understanding of the biogeochemical processes of biochar for its application in soil quality improvement and remediation.

Reactivity of Pyrogenic Carbonaceous Matter (PCM) in mediating environmental reactions: Current knowledge and future trends

Pyrogenic Carbonaceous Matter (PCM; e.g., black carbon, biochar, and activated carbon) are solid residues from incomplete combustion of fossil fuel or biomass. They are traditionally viewed as inert adsorbents for sequestering contaminants from the aqueous phase or providing surfaces for microbes to grow. In this account, we reviewed the recently discovered reactivity of PCM in promoting both chemical and microbial synergies that are important in pollutant transformation, biogeochemical processes of redox-active elements, and climate change mitigation with respect to the interaction between biochar and nitrous oxide (N2O). Moreover, we focused on our group’s work in the PCM-enhanced abiotic transformation of nitrogenous and halogenated pollutants and conducted in-depth analysis of the reaction pathways. To understand what properties of PCM confer its reactivity, our group pioneered the use of PCM-like polymers, namely conjugated microporous polymers (CMPs), to mimic the performance of PCM. This approach allows for the controlled incorporation of specific surface properties (e.g., quinones) into the polymer network during the polymer synthesis. As a result, the relationship between specific characteristics of PCM and its reactivity in facilitating the decay of a model pollutant was systematically studied in our group’s work. The findings summarized in this account help us to better understand an overlooked environmental process where PCM synergistically interacts with various environmental reagents such as hydrogen sulfide and water. Moreover, the knowledge gained in these studies could inform the design of a new generation of reactive carbonaceous materials with tailored properties that are highly efficient in contaminant removal.

Microcystins: Biogenesis, Toxicity, Analysis, and Control.

Microcystins are cyclic peptide toxins formed by cyanobacteria. These toxins are recognized for their association with algal blooms, posing a significant threat to ecosystems and drinking water quality. Due to the growing environmental concerns they raise, a comprehensive review on microcystins' genesis, toxicity, and analytical methods for their quantitative determination is outlined. Genes, including the mcyABC cluster, regulate microcystin biogenesis. Bioanalytical experiments have identified key environmental factors, such as temperature and nitrogen availability, that promote microcystin production. Microcystin toxicity is explored based on its modulatory effects on protein phosphatases 1 and 2A in specific tissues and organs. Additionally, biochemical mechanisms of chelation, transportation, resultant oxidative stress, and tumor promotion abilities of microcystins are also discussed. Various analytical methods to separate, detect, and quantify microcystins, including the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy, and chromatographic platforms-linked tandem mass spectrometry (LC-MS) for unequivocal structural identification, are also reviewed. Since control of microcystins in water is of great necessity, both water treatment and mechanisms of abiotic transformation and microbial degradation are also discussed.

Formalin-preserved zooplankton are not reliable for historical reconstructions of methylmercury bioaccumulation

Time-series measurements of methylmercury (MeHg) concentrations in short-lived planktic animals, such as copepods, could allow for an evaluation of mercury (Hg) inputs and transferability to organisms in marine environments. If reliable, MeHg measurements in formalin-preserved marine animals could offer insights into past environmental MeHg levels. In the present study, we examined whether the amount of MeHg changed over time in formalin-preserved copepods for two species, Acartia tonsa, and Temora longicornis. Over a 51 (A. tonsa) and 7 (T. longicornis) week incubation, we found significant changes in MeHg content in both copepods, while the timing of these changes differed between species. Furthermore, we investigated the mechanism behind these temporal changes through a separate incubation experiment of formalin spiked with two levels of organic matter (OM), and stable-isotope-enriched Hg tracers. We found that the methylation of an inorganic 199Hg tracer was significantly higher in OM-enriched solutions in comparison to a control seawater-formalin solution. Our results suggest that formalin-preserved copepods are not fit for studies of past trends due to ongoing and unpredictable abiotic transformations of Hg in chemically preserved animal tissue.

Multi-elemental C-Br-Cl isotope analysis for characterizing biotic and abiotic transformations of 1-bromo-2-chloroethane (BCE)

Multi-elemental C-Br-Cl compound-specific isotope analysis was applied for characterizing abiotic and biotic degradation of the environmental pollutant 1-bromo-2-chloroethane (BCE). Isotope effects were determined in the model processes following hydrolytic dehalogenation and dihaloelimination pathways as well as in a microcosm experiment by the microbial culture from the contaminated site. Hydrolytic dehalogenation of BCE under alkaline conditions and by DhaA enzyme resulted in similar dual isotope slopes (ɅC/Br 21.9 ± 4.7 and 19.4 ± 1.8, respectively, and ɅC/Cl ~ ∞). BCE transformation by cyanocobalamin (B12) and by Sulfurospirillum multivorans followed dihaloelimination and was accompanied by identical, within the uncertainty range, dual isotope slopes (ɅC/Br 8.4 ± 1.7 and 7.9 ± 4.2, respectively, and ɅC/Cl 2.4 ± 0.3 and 1.5 ± 0.6, respectively). Changes over time in the isotope composition of BCE from the contaminated groundwater showed only a slight variation in δ13C values and were not sufficient for the elucidation of the BCE degradation pathway in situ. However, an anaerobic microcosm experiment with the enrichment cultures from the contaminated groundwater presented dual isotope slopes similar to the hydrolytic pathway, suggesting that the potential for BCE degradation in situ by the hydrolytic dehalogenation pathway exists in the contaminated site.

Humic Substances Mediate Anaerobic Methane Oxidation Linked to Nitrous Oxide Reduction in Wetland Sediments.

Humic substances are redox-active organic molecules, which play pivotal roles in several biogeochemical cycles due to their electron-transferring capacity involving multiple abiotic and microbial transformations. Based on the redox properties of humic substances, and the metabolic capabilities of microorganisms to reduce and oxidize them, we hypothesized that they could mediate the anaerobic oxidation of methane (AOM) coupled to the reduction of nitrous oxide (N2O) in wetland sediments. This study provides several lines of evidence indicating the coupling between AOM and the reduction of N2O through an extracellular electron transfer mechanism mediated by the redox active functional groups in humic substances (e.g., quinones). We found that the microbiota of a sediment collected from the Sisal wetland (Yucatán Peninsula, southeastern Mexico) was able to reduce N2O (4.6 ± 0.5 μmol N2O g sed.–1 day–1) when reduced humic substances were provided as electron donor in a close stoichiometric relationship. Furthermore, a microbial enrichment derived from the wetland sediment achieved simultaneous 13CH4 oxidation (1.3 ± 0.1 μmol 13CO2 g sed.–1 day–1) and N2O reduction (25.2 ± 0.5 μmol N2O g sed.–1 day–1), which was significantly dependent on the presence of humic substances as an extracellular electron shuttle. Taxonomic characterization based on 16S rRNA gene sequencing revealed Acinetobacter (a ɣ-proteobacterium), the Rice Cluster I from the Methanocellaceae and an uncultured archaeon from the Methanomicrobiaceae family as the microbes potentially involved in AOM linked to N2O reduction mediated by humic substances. The findings reported here suggest that humic substances might play an important role to prevent the emission of greenhouse gases (CH4 and N2O) from wetland sediments. Further efforts to evaluate the feasibility of this novel mechanism under the natural conditions prevailing in ecosystems must be considered in future studies.

Evidence for extensive anaerobic dechlorination and transformation of the pesticide chlordecone (C10Cl10O) by indigenous microbes in microcosms from Guadeloupe soil.

The historic use of chlordecone (C10Cl10O) as a pesticide to control banana weevil infestations has resulted in pollution of large land areas in the French West Indies. Although currently banned, chlordecone persists because it adsorbs strongly to soil and its complex bis-homocubane structure is stable, particularly under aerobic conditions. Abiotic chemical transformation catalyzed by reduced vitamin B12 has been shown to break down chlordecone by opening the cage structure to produce C9 polychloroindenes. More recently these C9 polychloroindenes were also observed as products of anaerobic microbiological transformation. To investigate the anaerobic biotransformation of chlordecone by microbes native to the French West Indies, microcosms were constructed anaerobically from chlordecone impacted Guadeloupe soil and sludge to mimic natural attenuation and eletron donor-stimulated reductive dechlorination. Original microcosms and transfers were incubated over a period of 8 years, during which they were repeatedly amended with chlordecone and electron donor (ethanol and acetone). Using LC-MS, chlordecone and degradation products were detected in all the biologically active microcosms. Observed products included monohydro-, dihydro- and trihydrochlordecone derivatives (C10Cl10-nO2Hn; n = 1,2,3), as well as “open cage” C9 polychloroindene compounds (C9Cl5-nH3+n n = 0,1,2) and C10 carboxylated polychloroindene derivatives (C10Cl4-nO2H4+n, n = 0–3). Products with as many as 9 chlorine atoms removed were detected. These products were not observed in sterile (poisoned) microcosms. Chlordecone concentrations decreased in active microcosms as concentrations of products increased, indicating that anaerobic dechlorination processes have occurred. The data enabled a crude estimation of partitioning coefficients between soil and water, showing that carboxylated intermediates sorb poorly and as a consequence may be flushed away, while polychlorinated indenes sorb strongly to soil. Microbial community analysis in microcosms revealed enrichment of anaerobic fermenting and acetogenic microbes possibly involved in anaerobic chlordecone biotransformation. It thus should be possible to stimuilate anaerobic dechlorination through donor amendment to contaminated soils, particularly as some metabolites (in particular pentachloroindene) were already detected in field samples as a result of intrinsic processes. Extensive dechlorination in the microcosms, with evidence for up to 9 Cl atoms removed from the parent molecule is game-changing, giving hope to the possibility of using bioremediation to reduce the impact of CLD contamination.

Abiotic and biotic transformation of torasemide - Occurrence of degradation products in the aquatic environment

The pharmaceutical torasemide is an important loop diuretic and was 2017 one of the ten most prescribed drugs in Germany. Despite its detection in different compartments of the urban water cycle including drinking water, no studies were so far performed to elucidate its fate in the environment and the occurrence of transformation products (TPs). Therefore, we investigated the phototransformation, microbial degradation, transformation with human liver microsomes and anodic oxidation of torasemide to obtain good coverage of environmentally relevant degradation products. Overall sixteen products were identified, covering the following reaction mechanisms: aromatic and aliphatic hydroxylation, including further oxidation to carboxylic acids and quinone imines, amide cleavage, N-dealkylation, N-dearylation, and sulfonamide hydrolysis to sulfonic acids. Especially the formation of quinone imines could be of concern as they are highly reactive electrophiles. Torasemide itself was observed in all investigated wastewater treatment plant (WWTP) samples and wastewater-impacted surface waters. The maximum detected concentration was about 350 ng L−1. Only three of the sixteen transformation products were generally observed in at least one of the samples and the most frequently detected TPs were the human metabolites hydroxytorasemide (TP 364a) and carboxytorasemide (TP 378a). The complete removal of TP 364a during wastewater treatment was in agreement with the results of microbial degradation experiments. TP 364a was most likely transformed into TP 378a, which was microbially less degraded in lab experiments. Based on estimated concentrations, TP 378a could reach about 1 μg L−1 in the investigated wastewater matrices.

Sorption and abiotic transformation of monensin by iron and manganese oxides

Monensin, an ionophore antibiotic, is commonly administered as a feed additive to cattle and poultry. A large percentage of the administered dose is excreted in animal waste, which is often applied to agricultural fields as fertilizer. The objective of this work is to gain insight into the fate of monensin in soil by investigating the interactions between monensin and common soil minerals, including sorption and transformation to unmonitored partial oxidation products. Batch sorption experiments across varying conditions (i.e., pH, ionic strength) and desorption experiments (i.e., methanol, PO43−, methyl tert-butyl ether) were used to determine the extent to which a selection of common redox-active soil minerals [birnessite (δ-MnO2), goethite (α-FeOOH), hematite (α-Fe2O3)] can bind and transform monensin. Monensin was bound by hematite (pH < 7.5, up to 7.5 mmol kg−1), goethite (pH < 7.5, up to 3.4 mmol kg−1), and birnessite (pH < 7, up to 0.1 mmol kg−1). Combined sorption and transformation were the greatest for hematite and the lowest for birnessite. Sorption to hematite was more reversible than to goethite. Each desorption from goethite recovered <10% of sorbed monensin, whereas desorption from hematite recovered up to 69% of sorbed monensin, dependent on the solution. The potential for iron and manganese (hydr)oxides to abiotically transform monensin through reductive dissolution to partial oxidation products was evaluated by mass spectral analysis following sorption experiments. Additionally, the dominant sorption mechanism was inferred through ATR-FTIR spectroscopy, via examination of the carboxylate peak separation differences, on goethite and hematite to be bridging bidentate.

Transformation of catechol coupled to redox alteration of humic acids and the effects of Cu and Fe cations

Humic substances are reactive during redox alteration. However, the role of this reactivity in the transformation of organic compounds and in carbon cycling in the environment is still unclear. Here, we used 14C-radioactive tracer to study abiotic transformation and humification of catechol, a representative of naturally occurring monomeric phenols and phenolic pollutants, in suspensions of humic acids (HAs) at original and H2/Pd-reduced redox states with flux of air (HAorg-Air and HAred-Air, respectively) or N2 (HAorg-N2 and HAred-N2, respectively) for 20 min in absence and presence of Cu(II) and Fe(II). Both HAorg and HAred can transform catechol in the absence of O2 to 19% and 25% of the initially applied amount, respectively. The transformation of catechol strongly increased when air was introduced, amounting to 75% in HAred-Air treatment and 43% in HAorg-Air treatment, owing to the generation of reactive oxygen species. Considerable amounts of catecholic carbons were incorporated into HAs (26% for HAred-Air and 19% for HAorg-Air), constituting humification of catechol. The presence of Cu(II) strongly inhibited the overall transformation and humification of catechol, although it significantly increased humification at the start of incubation. The presence of Fe(II) overall enhanced both the transformation and humification. The results provide first insights into the impacts of redox alteration of humic substances together with the presence of metal ions with variable valences on the fate of phenolic compounds in the environment. This study points out that redox alteration-induced abiotic transformation may be one important process for dissipation of phenolic pollutants and humification of phenolic carbons in environments rich in HAs and subject to redox fluctuation.

Effect of Microbial Biomass and Humic Acids on Abiotic and Biotic Magnetite Formation.

Magnetite (Fe3O4) is an environmentally ubiquitous mixed-valent iron (Fe) mineral, which can form via biotic or abiotic transformation of Fe(III) (oxyhydr)oxides such as ferrihydrite (Fh). It is currently unclear whether environmentally relevant biogenic Fh from Fe(II)-oxidizing bacteria, containing cell-derived organic matter, can transform to magnetite. We compared abiotic and biotic transformation: (1) abiogenic Fh (aFh); (2) abiogenic Fh coprecipitated with humic acids (aFh-HA); (3) biogenic Fh produced by phototrophic Fe(II)-oxidizer Rhodobacter ferrooxidans SW2 (bFh); and (4) biogenic Fh treated with bleach to remove biogenic organic matter (bFh-bleach). Abiotic or biotic transformation of Fh was promoted by Feaq2+ or Fe(III)-reducing bacteria. Feaq2+-catalyzed abiotic reaction with aFh and bFh-bleach led to complete transformation to magnetite. In contrast, aFh-HA only partially (68%) transformed to magnetite, and bFh (17%) transformed to goethite. We hypothesize that microbial biomass stabilized bFh against reaction with Feaq2+. All four Fh substrates were transformed into magnetite during biotic reduction, suggesting that Fh remains bioavailable even when associated with microbial biomass. Additionally, there were poorly ordered magnetic components detected in the biogenic end products for aFh and aFh-HA. Nevertheless, abiotic transformation was much faster than biotic transformation, implying that initial Feaq2+ concentration, passivation of Fh, and/or sequestration of Fe(II) by bacterial cells and associated biomass play major roles in the rate of magnetite formation from Fh. These results improve our understanding of factors influencing secondary mineralization of Fh in the environment.

Spatio-temporal distribution and transformation of 17α- and 17β-estradiol in sterilized soil: A column experiment

The environmental behaviors of steroid estrogens (SEs) associated with land irrigation and application are of critical concern worldwide. Understanding the spatio-temporal distribution and transformation process of these estrogenic compounds in soil is greatly significant. In this study, laboratory soil column experiments were conducted to investigate and explore the migration and abiotic transformation of 17α-estradiol (17α-E2) and 17β-estradiol (17β-E2) over spatial and time scales. Results indicated that the migration tendency of 17α-E2 and 17β-E2 was similar. Discrepancies in transport for different SEs groups might be due to the competitive sorption and isomeric transformation in the binary-solute system. 17α-E2 and 17β-E2 can also undergo the abiotic transformation during soil column transport. The soil with naturally abundant mineral substances (e.g., iron and manganese oxides) indicated that E2 isomers tended to mineral-promoted racemization, oxidation, reduction, and radical coupling reactions. Some possible transformation products (e.g., SE239, E2378, and SE dimer476) were identified and proposed in soil samples. Compared to the single compound tests, the estimated 17β-estradiol equivalency (EEQ) values of E2 mixture were higher during SEs migration process.

Reductive transformations of dichloroacetamide safeners: effects of agrochemical co-formulants and iron oxide + manganese oxide binary-mineral systems.

The toxic effects of herbicides are often incompletely selective and can harm crops. Safeners are "inert" ingredients commonly added to herbicide formulations to protect crops from herbicide-induced injury. Dichloroacetamide safeners have been previously shown to undergo reductive dechlorination in anaerobic abiotic systems containing an iron (hydr)oxide mineral (goethite or hematite) amended with Fe(ii). Manganese oxides (e.g., birnessite) are important redox-active species that frequently co-occur with iron (hydr)oxides, yet studies examining the effects of more than one mineral on transformations of environmental contaminants are rare. Herein, we investigate the reactivity of dichloroacetamide safeners benoxacor, furilazole, and dichlormid in binary-mineral, anaerobic systems containing Fe(ii)-amended hematite and birnessite. As the molar ratio of Fe(ii)-to-Mn(iv) oxide increased, the transformation rate of benoxacor and furilazole increased. The safener dichlormid did not transform appreciably over the sampling period (6 hours). The concentration of pH buffer ([MOPS] = 10-50 mM), ionic strength ([NaCl] = 10-200 mM), and order of solute addition (e.g., safener followed by Fe(ii) or vice versa) do not appreciably affect transformation rates of the examined dichloroacetamide safeners in Fe(ii) + hematite slurries. The presence of agrochemical co-formulants, including the herbicide S-metolachlor and three surfactants, in solutions containing Cr(H2O)62+ (as a model homogeneous reductant) also did not substantially influence rates of safener transformation. This study is among the first to examine laboratory systems of intermediate complexity (e.g., systems containing mixtures of agrochemical co-formulants or mineral phases) when assessing the environmental fate of emerging contaminants such as dichloroacetamide safeners.