Compound-Specific Carbon, Nitrogen, and Hydrogen Isotope Analysis to Characterize Aerobic Biodegradation of 2,3-Dichloroaniline by a Mixed Enrichment Culture.

Compound-specific isotope analysis (CSIA) is an established tool to track the in situ transformation of organic chemicals at contaminated sites. In this work, we evaluated the potential of multi-element CSIA to assess biodegradation of 2,3-dichloroaniline (2,3-DCA), which is a major industrial feedstock. Using controlled laboratory experiments, we determined, for the first time, negligible carbon (<0.5‰) and hydrogen (<10‰) isotope fractionation and a significant inverse nitrogen isotope fractionation (>10‰) during aerobic 2,3-DCA biodegradation by a mixed enrichment culture. The tentative identification of a glutamate conjugate of 2,3-DCA as a reaction intermediate indicates that the initial multistep enzymatic reaction may be rate-limiting. The formation of the glutamate adduct would increase the bond energy at the N atom, thus likely explaining the observed inverse N isotope fractionation. The corresponding nitrogen enrichment factor was +6.8 ± 0.6‰. This value was applied to investigate the in situ 2,3-DCA biodegradation at a contaminated site where the carbon and nitrogen isotope signatures from field samples suggested similar aerobic processes by native microorganisms. Under the assumption of the applicability of the Rayleigh model in a pilot wetland treating contaminated groundwater, the extent of biodegradation was estimated to be up to 80-90%. This study proposes multi-element CSIA as a novel application to study 2,3-DCA fate in groundwater and surface water and provides insights into biodegradation pathways.

Compound-Specific Carbon, Hydrogen, and Nitrogen Isotope Analysis of Nitro- and Amino-Substituted Chlorobenzenes in Complex Aqueous Matrices.

Compound-specific isotope analysis (CSIA) is an established tool to study the fate of legacy groundwater contaminants but is only emerging for nonconventional contaminants, e.g., nitro- and amino-substituted chlorobenzenes that are widely used as industrial feedstock and the target of this work. To date, CSIA of the target compound groups used special combustion interfaces and the potential matrix interferences in environmental samples has not been assessed. We validated CSIA methods for δ13C, δ2H, and δ15N of four analytes from each chemical group and developed a solid-phase extraction (SPE) method to minimize matrix interferences during preconcentration of complex aqueous samples. The SPE recovery was >80% and the method quantification limits of SPE-CSIA for δ13C, δ2H, and δ15N were 0.03-0.57, 1.3-2.7, and 3.4-10.2 µM aqueous-phase concentrations, respectively, using 2 L of spiked MQ water. The SPE-CSIA procedure showed negligible isotope fractionation for δ13C (≤0.5‰), δ15N (≤0.5‰), and δ2H (≤5‰ for nitroaromatics and ≤10‰ for aminoaromatics). In addition, solvent evaporation, water sample storage up to 7 months, and SPE extract storage for 1.5 years did not change analytes' δ13C signatures beyond ±0.5‰. However, to avoid significant δ2H and δ15N fractionation of aminoaromatics, cartridge breakthrough should be avoided and SPE preconcentration must be conducted at pH > pKa + 2. Application of the method at a contaminated site showed excellent precision, at ≤0.3‰ for C and N, and ≤1.5‰ for H. The methods validated here now allow the use of multielement CSIA to track the environmental fate of nitro- and amino-substituted chlorobenzenes in complex aqueous samples.

Modeling multi-year phosphorus dynamics in a bioretention cell: Phosphorus partitioning, accumulation, and export.

Phosphorus (P) export from urban areas via stormwater runoff contributes to eutrophication of downstream aquatic ecosystems. Bioretention cells are a Low Impact Development (LID) technology promoted as a green solution to attenuate urban peak flow discharge, as well as the export of excess nutrients and other contaminants. Despite their rapidly growing implementation worldwide, a predictive understanding of the efficiency of bioretention cells in reducing urban P loadings remains limited. Here, we present a reaction-transport model to simulate the fate and transport of P in a bioretention cell facility in the greater Toronto metropolitan area. The model incorporates a representation of the biogeochemical reaction network that controls P cycling within the cell. We used the model as a diagnostic tool to determine the relative importance of processes immobilizing P in the bioretention cell. The model predictions were compared to multi-year observational data on 1) the outflow loads of total P (TP) and soluble reactive P (SRP) during the 2012-2017 period, 2) TP depth profiles collected at 4 time points during the 2012-2019 period, and 3) sequential chemical P extractions performed on core samples from the filter media layer obtained in 2019. Results indicate that exfiltration to underlying native soil was principally responsible for decreasing the surface water discharge from the bioretention cell (63 % runoff reduction). From 2012 to 2017, the cumulative outflow export loads of TP and SRP only accounted for 1 % and 2 % of the corresponding inflow loads, respectively, hence demonstrating the extremely high P reduction efficiency of this bioretention cell. Accumulation in the filter media layer was the predominant mechanism responsible for the reduction in P outflow loading (57 % retention of TP inflow load) followed by plant uptake (21 % TP retention). Of the P retained within the filter media layer, 48 % occurred in stable, 41 % in potentially mobilizable, and 11 % in easily mobilizable forms. There were no signs that the P retention capacity of the bioretention cell was approaching saturation after 7 years of operation. The reactive transport modeling approach developed here can in principle be transferred and adapted to fit other bioretention cell designs and hydrological regimes to estimate P surface loading reductions at a range of temporal scales, from a single precipitation event to long-term (i.e., multi-year) operation.

Is In-Service Granular Activated Carbon Biologically Active? An Evaluation of Alternative Experimental Methods to Distinguish Adsorption and Biodegradation in GAC.

In-service granular activated carbon (GAC) may transform into biological activated carbon (BAC) and remove contaminants through both adsorption and biodegradation, but it is difficult to determine its biodegradative capacity. One approach to understand the GAC biodegradative capacity is to compare the performance between unsterilized and sterilized GAC, but the sterilization methods may not ensure effective microbial inhibition and may affect adsorption. This study identified the 14C-glucose respiration rate as the best metric to evaluate the effectiveness of three sterilization methods: sodium azide addition, autoclaving, and γ irradiation. The sterilization protocols were refined, including continuously feeding 300 mg/L of sodium azide, three cycles of autoclaving, and 10-12 kGy of γ irradiation. Parallel minicolumn tests were conducted to identify sodium azide addition as the most broadly effective sterilization method with an insignificant effect on adsorption in most cases, except for the adsorption of anionic compounds under certain conditions. Nevertheless, this problem was solved by decreasing the azide dosage as long as it is still sufficient to provide effective microbial inhibition. This study helps to develop an approach that differentiates adsorption and biodegradation in GAC, which could be used by future studies to advance our understanding of BAC filtration.

Harnessing plant-microbiome interactions for bioremediation across a freshwater urbanization gradient.

Urbanization impacts land, air, and water, creating environmental gradients between cities and rural areas. Urban stormwater delivers myriad co-occurring, understudied, and mostly unregulated contaminants to aquatic ecosystems, causing a pollution gradient. Recipient ecosystems host interacting species that can affect each others' growth and responses to these contaminants. For example, plants and their microbiomes often reciprocally increase growth and contaminant tolerance. Here, we identified ecological variables affecting contaminant fate across an urban-rural gradient using 50 sources of the aquatic plant Lemna minor (duckweed) and associated microbes, and two co-occurring winter contaminants of temperate cities, benzotriazole and salt. We conducted experiments totalling >2,500 independent host-microbe-contaminant microcosms. Benzotriazole and salt negatively affected duckweed growth, but not microbial growth, and duckweeds maintained faster growth with their local, rather than disrupted, microbiota. Benzotriazole transformation products of plant, microbial, and phototransformation pathways were linked to duckweed and microbial growth, and were affected by salt co-contamination, microbiome disruption, and source sites of duckweeds and microbes. Duckweeds from urban sites grew faster and enhanced phytotransformation, but supported less total transformation of benzotriazole. Increasing microbial community diversity correlated with greater removal of benzotriazole, but taxonomic groups may explain shifts across transformation pathways: the genus Aeromonas was linked to increasing phototransformation. Because benzotriazole toxicity could depend on amount and type of in situ transformation, this variation across duckweeds and microbes could be harnessed for better management of urban stormwater. Broadly, our results demonstrate that plant-microbiome interactions harbour manipulable variation for bioremediation applications.

Implications of polar organic chemical integrative sampler for high membrane sorption and suitability of polyethersulfone as a single-phase sampler.

Polar organic chemical integrative sampler (POCIS) contains sorbent, which is typically enclosed between two polyethersulfones (PES) membranes. A significant PES uptake is reported for many contaminants, yet, aqueous concentration is mainly correlated with the sorbent uptake using first-order kinetics. Under high PES sorption, the first-order kinetics often provide erroneous sampling rate for the sorbent phase due to increased membrane resistance. This work evaluated the uptake of four high PES sorbing chemicals, i.e., three Cl- and CH3-substituted nitrobenzenes and one chlorinated aniline using POCIS and the potential of a single-phase PES sampler using laboratory experiments. POCIS calibration results demonstrated that both sorbent and membrane had similar affinity for the target compounds. A rapid PES sorption occurred in the earlier days (<7 days) followed by a gradual increase in the PES phase concentration (equilibrium not achieved after 60 days). Especially, the membrane was the primary sink for 3,4-dichloroaniline and 3,4-dichloronitrobenzene for up to 14 and 31 days, respectively. On the other hand, the single-phase PES sampler showed similar mass uptake as POCIS and reached equilibrium within 19 days under static condition, indicating its potential suitability in the equilibrium regime. PES-water partition coefficient of the target compounds was between 1.2 and 6.5 L/g. Finally, we present a poly-parameter linear-free energy relationship (pp-LFER) using published data to predict the PES-water partition coefficients. The pp-LFER models showed moderate predictability as indicated by R2adj values between 0.7 and 0.9 for both internal and external data set consisting of a wide range of hydrophobic and hydrophilic compounds (-0.1 ≤ logKOW ≤ 7.4). The proposed pp-LFER model can be used to screen high PES-sorbing chemicals to increase the reliability and accuracy of aqueous concentration prediction from POCIS sampling and to select the most appropriate sampling approach for new compounds.

Evaluating perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) removal across granular activated carbon (GAC) filter-adsorbers in drinking water treatment plants.

Granular activated carbon (GAC) was harvested from six filter-adsorbers that are used for taste and odour control in three drinking water treatment plants in Ontario, Canada, and evaluated for the removal of perfluorooctanic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) using minicolumn tests under different operational conditions. Parallel column tests were conducted using unsterilized GAC and sterilized GAC to distinguish adsorption from potential biodegradation of PFOA and PFOS across the GAC. It was observed that the GAC could achieve approximately 20% to 55% of PFOA and PFOS removal even after a long period of GAC operation (e.g., 6 years). There was no evidence of PFOA and PFOS biodegradation, so the removal in GAC can be attributed solely to adsorption under the conditions tested. However, in one location, there was evidence suggesting both removal and formation of PFOS and PFOA across the GAC, with the formation presumably due to the biotransformation of pre-existing precursors in the source water. Additionally, GAC service time and empty bed contact time (EBCT) were identified to be important factors that could affect the removal of PFOA and PFOS. Based on this information, an empirical model was proposed to predict PFOA and PFOS removal in GAC filter-adsorbers as a function of GAC service time and EBCT. This study provides useful information for utilities that have installed GAC for taste and odour control but may consider per- and polyfluoroalkyl substances (PFAS) removal as an additional voluntary objective or due to more stringent guidelines.

Stormwater Bioretention Cells Are Not an Effective Treatment for Persistent and Mobile Organic Compounds (PMOCs).

Bioretention cells are a stormwater management technology intended to reduce the quantity of water entering receiving bodies. They are also used to reduce contaminant releases, but their performance is unclear for hydrophilic persistent and mobile organic compounds (PMOCs). We developed a novel eight-compartment one-dimensional (1D) multimedia model of a bioretention cell ("Bioretention Blues") and applied it to a spike and recovery experiment conducted on a system near Toronto, Canada, involving PMOC benzotriazole and four organophosphate esters (OPEs). Compounds with (log DOC) (organic carbon-water distribution coefficients) < ∼2.7 advected through the system, resulting in infiltration or underdrain flow. Compounds with log DOC > 3.8 were mostly sorbed to the soil, where subsequent fate depended on transformation. For compounds with 2.7 ≤ log DOC ≤ 3.8, sorption was sensitive to event size and compound-specific diffusion parameters, with more sorption expected for smaller rain events and for compounds with larger diffusion coefficients. Volatilization losses were minimal for all compounds tested. Direct uptake by vegetation also played a negligible role regardless of the compounds' physicochemical properties. Nonetheless, model simulations showed that vegetation could play a role by increasing transpiration, thereby increasing sorption to the bioretention soil and reducing PMOC release. Model results suggest design modifications to bioretention cells.

Triclosan uptake and transformation by the green algae Euglena gracilis strain Z.

Triclosan is an antimicrobial chemical present in consumer products that is frequently detected in aquatic environments. In this research, we investigated the role of a common freshwater microalgae species, Euglena gracilis for triclosan uptake and transformation in open-water treatment wetlands. Lab-scale wetland bioreactors were created under various conditions of light (i.e., continuous (white) light, red light, and in the dark), media (i.e., wetland, autoclaved wetland, Milli-Q, and growth media water), and presence or absence of algae. Triclosan and its potential transformation products were identified in the water and algae phases. Triclosan transformation occurred most rapidly with reactors that received continuous (white) light, with pseudo first-order rate constants, k, ranging from 0.035 to 0.292 day-1. This indicates that phototransformation played a major role in triclosan transformation during the day, despite light screening by algae. Algae contributed to the uptake and transformation of triclosan in all reactors, and algae and bacteria both contributed to triclosan biotransformation under dark conditions, representative of nighttime conditions. Some transformation products were formed and further transformed, e.g., triclosan-O-sulfate, methoxy and diglucosyl conjugate of hydroxylated triclosan, and dimethoxy and glucosyl conjugate of 2,4-dichlorophenol, suggesting their minimal accumulation over the 25 days of the experiments. This study shows that the combined action of light, microbes, and algae allows the safe transfer and transformation of triclosan in open-water treatment wetlands.

Evaluating the relative adsorption and biodegradation of 2-methylisoborneol and geosmin across granular activated carbon filter-adsorbers.

This study investigated the relative contributions of adsorption vs. biodegradation towards 2-methylisoborneol (MIB) and geosmin removal in the granular activated carbon (GAC) harvested from six filter-adsorbers in three drinking water treatment plants in the Great Lakes region. Column tests using azide-treated (sterilized) and untreated GAC in parallel were used to isolate the two effects. It was identified that substantial MIB and geosmin biodegradation in the GAC was occurring in one location, and that GAC in some cases had significant adsorption capacity after as much as 9 years of operation. Four alternative biological parameters (adenosine triphosphate, esterase activity, phosphatase activity, and 14C-glucose respiration rate) were measured to quantify the biological activity of the GAC, and 14C-glucose respiration rate was identified to be a potential indicator for GAC biodegradative capacity in terms of MIB, geosmin, and dissolved organic carbon. Several potential MIB and geosmin biodegradation products were also identified using non-targeted screening analysis. By using the new tools identified in this study, we can begin to better understand where adsorption vs. biodegradation may predominate under real-world conditions (e.g., different temperatures, influent concentrations, and empty bed contact time), leading ultimately to more cost-effective use of GAC.

Automatic quantification and classification of microplastics in scanning electron micrographs via deep learning.

Microplastics quantification and classification are demanding jobs to monitor microplastic pollution and evaluate the potential health risks. In this paper, microplastics from daily supplies in diverse chemical compositions and shapes are imaged by scanning electron microscopy. It offers a greater depth and finer details of microplastics at a wider range of magnification than visible light microscopy or a digital camera, and permits further chemical composition analysis. However, it is labour-intensive to manually extract microplastics from micrographs, especially for small particles and thin fibres. A deep learning approach facilitates microplastics quantification and classification with a manually annotated dataset including 237 micrographs of microplastic particles (fragments or beads) in the range of 50 µm-1 mm and fibres with diameters around 10 µm. For microplastics quantification, two deep learning models (U-Net and MultiResUNet) were implemented for semantic segmentation. Both significantly outmatched conventional computer vision techniques and achieved a high average Jaccard index over 0.75. Especially, U-Net was combined with object-aware pixel embedding to perform instance segmentation on densely packed and tangled fibres for further quantification. For shape classification, a fine-tuned VGG16 neural network classifies microplastics based on their shapes with high accuracy of 98.33%. With trained models, it takes only seconds to segment and classify a new micrograph in high accuracy, which is remarkably cheaper and faster than manual labour. The growing datasets may benefit the identification and quantification of microplastics in environmental samples in future work.

Understanding adsorption and biodegradation in granular activated carbon for drinking water treatment: A critical review.

Drinking water treatment plants use granular activated carbon (GAC) to adsorb and remove trace organics, but the GAC has a limited lifetime in terms of adsorptive capacity and needs to be replaced before it is exhausted. Biological degradation of target contaminants can also occur in GAC filters, which might allow the GAC to remain in service longer than expected. However, GAC biofiltration remains poorly understood and unpredictable. To increase the understanding of adsorption and biodegradation in GAC, previous studies have conducted parallel column tests that use one column of GAC (potentially biologically active) to assess overall removal via both adsorption and biodegradation, and one column with either sterilized GAC or biological non-adsorbing media to assess adsorption or biodegradation alone. Mathematical models have also been established to give insight into the adsorption and biodegradation processes in GAC. In this review, the experimental and modeling approaches and results used to distinguish between the role of adsorption and biodegradation were summarized and critically discussed. We identified several limitations: (1) using biological non-adsorbing media in column tests might lead to non-representative extents of biodegradation; (2) sterilization methods may not effectively inhibit biological activity and may affect adsorption; (3) using virgin GAC coated with biofilm could overestimate adsorption; (4) potential biofilm detachment during column experiments could lead to biased results; (5) the parallel column test approach itself is not universally applicable; (6) competitive adsorption was neglected by previous models; (7) model formulations were based on virgin GAC only. To overcome these limitations, we proposed four new approaches: the use of gamma irradiation for sterilization, a novel minicolumn test, compound-specific isotope analysis to decipher the role of adsorption and biodegradation in situ, and a new model to simulate trace organic adsorption and biodegradation in a GAC filter .

Trace Organic Contaminant Transfer and Transformation in Bioretention Cells: A Field Tracer Test with Benzotriazole.

Bioretention cells can effectively infiltrate stormwater runoff and partly remove conventional water contaminants. A field tracer injection experiment in a conventionally designed bioretention cell was used to investigate the fate of benzotriazole, a model trace organic contaminant, during and between runoff events. Moderate (29%) benzotriazole load reductions were measured during the 6 h long injection experiment. The detection of 1-methyl benzotriazole, hydroxy benzotriazole, and methoxy benzotriazole provided in situ evidence of some rapid benzotriazole microbial transformation during the tracer test and more importantly between the events. The detection of benzotriazole alanine and benzotriazole acetyl alanine also showed fast benzotriazole phytotransformation to amino acid conjugates during the tracer test and suggests further transformation of phytotransformation products between events. These data provide conclusive full-scale evidence of benzotriazole microbial and phytotransformation in bioretention cells. Non-target chemical analysis revealed the presence of a diverse range of trace organic contaminants in urban runoff and exiting the bioretention cell, including pesticides and industrial, household, and pharmaceutical compounds. We have demonstrated the in situ potential of urban green infrastructure such as bioretention cells to eliminate polar trace organic contaminants from stormwater. However, targeted design and operation strategies, for example, hydraulic control and the use of soil amendments, should be incorporated for improved bioretention cell performance for such compounds.

Carbon, hydrogen and nitrogen stable isotope fractionation allow characterizing the reaction mechanisms of 1H-benzotriazole aqueous phototransformation.

1H-benzotriazole is part of a larger family of benzotriazoles, which are widely used as lubricants, polymer stabilizers, corrosion inhibitors, and anti-icing fluid components. It is frequently detected in urban runoff, wastewater, and receiving aquatic environments. 1H-benzotriazole is typically resistant to biodegradation and hydrolysis, but can be transformed via direct photolysis and photoinduced mechanisms. In this study, the phototransformation mechanisms of 1H-benzotriazole were characterized using multi-element compound-specific isotope analysis (CSIA). The kinetics, transformation products, and isotope fractionation results altogether revealed that 1H-benzotriazole direct photolysis and indirect photolysis induced by OH radicals involved two alternative pathways. In indirect photolysis, aromatic hydroxylation dominated and was associated with small carbon (εC = -0.65 ± 0.03‰), moderate hydrogen (εH = -21.6‰), and negligible nitrogen isotope enrichment factors and led to hydroxylated forms of benzotriazole. In direct photolysis of 1H-benzotriazole, significant nitrogen (εN = -8.4 ± 0.4 to -4.2 ± 0.3‰) and carbon (εC = -4.3 ± 0.2 to -1.64 ± 0.04‰) isotope enrichment factors indicated an initial N-N bond cleavage followed by nitrogen elimination with a C-N bond cleavage. The results of this study highlight the potential for multi-element CSIA application to track 1H-benzotriazole degradation in aquatic environments.

Bioretention cells remove microplastics from urban stormwater.

Microplastic pathways in the environment must be better understood to help select appropriate mitigation strategies. In this 2-year long field study, microplastics were characterized and quantified in urban stormwater runoff and through a bioretention cell, a type of low impact development infrastructure. Concentrations of microparticles ranged from below the detection limit to 704 microparticles/L and the dominant morphology found were fibers. High rainfall intensity and longer antecedent dry days resulted in larger microparticle concentrations. In addition, atmospheric deposition was a source of microplastics to urban runoff. Overall, these results demonstrate that urban stormwater runoff is a concentrated source of microplastics whose concentrations depend on specific climate variables. The bioretention cell showed an 84% decrease in median microparticle concentration in the 106-5,000 µm range, and thus is effective in filtering out microplastics and preventing their spread to downstream environments. Altogether, these results highlight the large contribution of urban stormwater runoff to microplastic contamination in larger aquatic systems and demonstrate the potential for current infiltration-based low impact development practices to limit the spread of microplastic contamination downstream.

Optimization of a solid-phase microextraction technique for chloro­ and nitro- substituted aromatic compounds using design of experiments.

A rapid and sensitive direct immersion solid-phase microextraction (SPME) technique for the analysis of seven chloro (Cl-) and nitro (NO2-) substituted anilines, toluenes, and nitrobenzenes from small volume (1.5 mL) aqueous samples was optimized for gas chromatography using Design of Experiments (DoE). Screening of the SPME factors was performed by a fractional factorial DoE, and the optimization of influential factors was achieved with a central composite multi-response surface DoE. Extraction time, pre-SPME agitation speed, extraction temperature, and desorption temperature were identified as significant factors and their values were set using a desirability function that maximized the extraction of the seven target analytes. Extraction time and agitation speed showed significant interactions for most analytes (α = 0.05). The relative standard deviations (RSDs) for within-day and between-day analyses were below 8%, suggesting that the method was repeatable and reproducible. The obtained limits of detection were in the low µg/L range (1-10) using a Flame Ionization Detector, far below what is needed for industrial contaminated sites (usually >1 mg/L). The optimized SPME method increased the analyte concentration up to 2-3 orders of magnitude compared with direct GC injection. The optimized SPME method was applied to two groundwater samples from a contaminated site in which the concentrations of three of the target analytes were ranged from 0.06 to 9.42 mg/L with RSDs <11%. When the concentrations of the target analytes in the sample matrix were higher than 0.5 mg/L, a competition for the SPME extraction sites was observed where analytes with higher affinity for the fiber material replaced the analytes with lower affinity. As a result, dilution of highly contaminated samples is recommended. This study provided for the first time an analytical method for the quantification of frequently co-occurring contaminants from the chloro­ and nitro- substituted aniline, toluene, and nitrobenzene families.

Sulfidated nano zerovalent iron (S-nZVI) for in situ treatment of chlorinated solvents: A field study.

Sulfidated nano zerovalent iron (S-nZVI), stabilized with carboxymethyl cellulose (CMC), was successfully synthesized on site and injected into the subsurface at a site contaminated with a broad range of chlorinated volatile organic compounds (cVOCs). Transport of CMC-S-nZVI to the monitoring wells, both downgradient and upgradient, resulted in a significant decrease in concentrations of aqueous-phase cVOCs. Short-term (0-17 days) total boron and chloride measurements indicated dilution and displacement in these wells. Importantly however, compound specific isotope analysis (CSIA), changes in concentrations of intermediates, and increase in ethene concentrations confirmed dechlorination of cVOCs. Dissolution from the DNAPL pool into the aqueous phase at the deepest levels (4.0-4.5 m bgs) was identifiable from the increased cVOCs concentrations during long-term monitoring. However, at the uppermost levels (∼1.5 m above the source zone) a contrasting trend was observed indicating successful dechlorination. Changes in cVOCs concentrations and CSIA data suggest both sequential hydrogenolysis as well as reductive ß-elimination as the possible transformation mechanisms during the short-term abiotic and long-term biotic dechlorination. One of the most positive outcomes of this CMC-S-nZVI field treatment is the non-accumulation of lower chlorinated VOCs, particularly vinyl chloride. Post-treatment soil cores also revealed significant decreases in cVOCs concentrations throughout the targeted treatment zones. Results from this field study show that sulfidation is a suitable amendment for developing more efficient nZVI-based in situ remediation technologies.

Resilience to multiple stressors in an aquatic plant and its microbiome.

PREMISE: Outcomes of species interactions, especially mutualisms, are notoriously dependent on environmental context, and environments are changing rapidly. Studies have investigated how mutualisms respond to or ameliorate anthropogenic environmental changes, but most have focused on nutrient pollution or climate change and tested stressors one at a time. Relatively little is known about how mutualisms may be altered by or buffer the effects of multiple chemical contaminants, which differ fundamentally from nutrient or climate stressors and are especially widespread in aquatic habitats. METHODS: We investigated the impacts of two contaminants on interactions between the duckweed Lemna minor and its microbiome. Sodium chloride (salt) and benzotriazole (a corrosion inhibitor) often co-occur in runoff to water bodies where duckweeds reside. We tested three L. minor genotypes with and without the culturable portion of their microbiome across field-realistic gradients of salt (3 levels) and benzotriazole (4 levels) in a fully factorial experiment (24 treatments, tested on each genotype) and measured plant and microbial growth. RESULTS: Stressors had conditional effects. Salt decreased both plant and microbial growth and decreased plant survival more as benzotriazole concentrations increased. In contrast, benzotriazole did not affect microbial abundance and even benefited plants when salt and microbes were absent, perhaps due to biotransformation into growth-promoting compounds. Microbes did not ameliorate duckweed stressors; microbial inoculation increased plant growth, but not at high salt concentrations. CONCLUSIONS: Our results suggest that multiple stressors matter when predicting responses of mutualisms to global change and that beneficial microbes may not always buffer hosts against stress.

Optimizing Constructed Wetlands for Safe Removal of Triclosan: A Box-Behnken Approach.

Traditional constructed wetland designs typically result in variable efficiencies for trace organic contaminant removal. In this work, we used a Box-Behnken experimental design for optimizing the conditions of pH, nitrate concentration, and dissolved organic carbon (DOC) concentration that would maximize the rate of triclosan phototransformation while minimizing the accumulation of toxic byproducts. Triclosan is a frequently detected and toxic antimicrobial agent present in many consumer and industrial products. The results showed that high pH values (9.9) and low DOC concentration (11 mg/L-) would maximize triclosan phototransformation rate while minimizing the accumulation of toxic byproducts. As long as DOC concentrations were larger than 33 mg/L, nitrate concentration did not show a significant effect on triclosan phototransformation rate. The major transformation products detected were 2,4-dichlorophenol and compounds with chemical formulas C12H8Cl2O2 and C12H9ClO3, resulting from a chlorine loss or replacement by a OH group. In addition, 4-chlorocatechol was mainly detected during direct photolysis and 2,8-dichlorodibenzo-p-dioxin was only found during direct photolysis at pH 8. This study showed that wetland efficiency at removing triclosan can theoretically be increased by limiting DOC-contributing factors, e.g., emergent vegetation, and supporting pH-increase processes, e.g., via algae growth or by incorporating alkaline geomedia.

Mechanisms of pharmaceutical and personal care product removal in algae-based wastewater treatment systems.

The widespread distribution of pharmaceuticals and personal care products (PPCPs), particularly in the built environment, has led to increased concern about their effects on both human and ecosystem health. In this research, we investigated the role of algae species Scenedesmus obliquus and Chlorella vulgaris in governing PPCP transfer and transformation mechanisms in algae-containing environments. Lab-scale algal bioreactors were created under various conditions of light, water matrix, and sterilization method to isolate and elucidate reaction mechanisms affecting carbamazepine, ibuprofen, gemfibrozil, and triclosan. The parent compounds and their potential transformation products were analyzed in both the water and algae phases. The results showed that ibuprofen was primarily biotransformed due to synergistic relationships between the algae and the bacteria. Ibuprofen biotransformation products tentatively identified as hydroxy-ibuprofen, carboxy-ibuprofen, and 4-isobutylcatechol were detected in several samples. In all the reactors exposed to light, triclosan underwent both phototransformation and biotransformation. Triclosan biotransformation took place in Scenedesmus obliquus, as demonstrated by the presence of triclosan-O-sulfate in the algae extracts. No evidence of significant carbamazepine and gemfibrozil transfer or transformation was observed under the experimental conditions tested. These results suggest that microalgal-bacterial consortia can facilitate PPCP transformation in algae-based passive water treatment systems.