Reaction of decabromodiphenyl ether with organo-modified clay-templated zero-valent iron in water-tetrahydrofuran solution: Nano- to micrometric scale effects.

Smectite clay-templated nanoscale zero-valent iron (CZVI) was modified with tetramethylammonium (TMA), trimethylphenylammonium (TMPA) and hexadecyltrimethylammonium (HDTMA) to achieve organoclay-templated ZVI (OCZVI). The reactivity of various OCZVIs was evaluated on the basis of degradation of decabromodiphenyl ether (DBDE) in tetrahydrofuran (THF)-water binary solution. Characterization of OCZVI interlayer at nanometric scale indicated that the clay particles had the domains with three basal spacings in the THF/water solution. In the 50 % THF solution TMPA modification promoted the formation of the domains with a basal spacing at 1.56 nm, which could promote the degradation of DBDE. At the micrometric scale, in the 90 % THF solution TMA and TMPA modification tended to enhance the aggregation of OCZVI particles, while the HDTMA modification reduced the aggregation, and high percentage of modification yielded viscous gel structures. The relatively rapid sedimentation processes in 90 % THF solution (compared to that in 50 % THF solution) and formation gel structures could reduce the access of DBDE to the interlayer reactive nZVIs, and lead to the significant reduction in reaction rate. These results provide important insights to the organo-modification on clays which could alter their orientations and dispersion in organic-water binary solution to achieve the desired reactivity on confined clay surfaces.

Bacterial community assembly and antibiotic resistance genes in soils exposed to antibiotics at environmentally relevant concentrations.

Understanding how bacterial community assembly and antibiotic resistance genes (ARGs) respond to antibiotic exposure is essential to deciphering the ecological risk of anthropogenic antibiotic pollution in soils. In this study, three loam soils with different land management (unmanured golf course, dairy-manured pasture, and swine-manured cornfield) were spiked with a mixture of 11 antibiotics at the initial concentration of 100 and 1000 µg kg-1 for each antibiotic and incubated over 132 days, mimicking a scenario of pulse disturbance and recovery in soils, with unspiked soil samples as the control treatment. The Infer Community Assembly Mechanisms by Phylogenetic-bin-based null model (iCAMP) analysis demonstrated that drift and dispersal limitation contributed to 57%-65% and 16%-25%, and homogeneous selection 12%-16% of soil bacterial community assembly. Interestingly, antibiotic exposure to 1000 µg kg-1 level significantly increased the contribution of drift to community assembly, largely due to the positive response from Acidobacteria-6 in the golf course and pasture soils and from Chthoniobacteraceae in the cornfield soil to the antibiotic exposure. However, ARG abundance and diversity in the three soils exhibited antibiotics-independent temporal fluctuations, but were associated with the changes in soil bacterial communities over time. This study provides the first insight into the relative contributions of different bacterial community assembly processes in soils upon antibiotic exposure at environmentally relevant concentrations.

Tetracycline accumulation in biofilms enhances the selection pressure on Escherichia coli for expression of antibiotic resistance.

Microorganisms are present as either biofilm or planktonic species in natural and engineered environments. Little is known about the selection pressure emanating from exposure to sub-minimal inhibitory concentration of antibiotics on planktonic vs. biofilm bacteria. In this study, an E. coli bioreporter was used to develop biofilms on glass and high-density polyethylene (HDPE) surfaces, and compared with the corresponding planktonic bacteria in antibiotic resistance expression when exposed to a range of µg/L levels of tetracycline. The antibiotic resistance-associated fluorescence emissions from biofilm E. coli reached up to 1.6 times more than those from planktonic bacteria. The intensively developed biofilms on glass surfaces caused the embedded bacteria to experience higher selection pressure and express more antibiotic resistance than those on HDPE surfaces. The temporal pattern of fluorescence emissions from biofilm E. coli was consistent with the biofilm-developing processes during the experimental period. The increased expression of antibiotic resistance from biofilm bacteria could be attributed to the high affinity of tetracycline with extracellular polymeric substances (EPS). The enhanced accumulation of tetracycline in biofilms could exert higher selection pressure on the embedded bacteria. These results suggest that in many natural and engineered systems the higher antibiotic resistance in biofilm bacteria could be attributed partially to the retention antibiotics by the EPS in biofilms.

Characterization of Plant Accumulation of Pharmaceuticals from Soils with Their Concentration in Soil Pore Water.

Predicting plant uptake of pharmaceuticals from soils is very challenging because many pharmaceuticals are ionizable compounds, which experience highly variable sorption/desorption and transformation processes in soils. This study aimed to elucidate how the equilibrium between sorbed and dissolved phases influences radish uptake of 15 pharmaceuticals from three soils with different properties. After 30 days of uptake, the accumulation of acetaminophen, carbamazepine, lamotrigine, carbadox, trimethoprim, and triclosan in radish ranked as Riddles > Capac > Spinks soil. In contrast, radish accumulation of caffeine, lincomycin, monensin, tylosin, sulfadiazine, and sulfamethoxazole exhibited the opposite order of Riddles < Capac < Spinks soil. Oxytetracycline and estrone demonstrated similar accumulation in radish grown in the three soils. Accumulation of pharmaceuticals in radish demonstrated no apparent relation with their concentration in soils. However, we identified strong positive correlation between pharmaceutical accumulation in radish and their corresponding concentration in soil pore water. These results reveal that pharmaceutical in soil pore water is the dominant fraction bioavailable to plant uptake. Relatively constant root concentration factors (RCFs) on the basis of pharmaceutical concentration in soil pore water, compared to the highly variable RCFs derived from soils, suggest that pore water-based RCF is superior for describing pharmaceutical accumulation in plants grown in soils. We recommend that pharmaceuticals in soil pore water should be evaluated and included in modeling their uptake by plants.

A coupled UV photolysis-biodegradation process for the treatment of decabrominated diphenyl ethers in an aerobic novel bioslurry reactor.

The commercial flame retardant is an emerging contaminant (EC) commonly found in soils and sediments. A coupled UV-photolysis-biodegradation process was used to decompose decabromodiphenyl ether (BDE-209) in clay slurries. A novel bioslurry bioreactor (NBB) was employed in which BDE-209 degradation was maximized by the simultaneous application of LED UVA irradiation and biodegradation by a mixed bacterial culture. The rate of BDE-209 degradation decreased in the order: coupled UV photolysis-biodegradation (1.31 × 10-2 day-1) > UV photolysis alone (1.10 × 10-2 day-1) > biodegradation alone (1.00 × 10-2 day-1). Degradation intermediates detected included hydroxylated polybrominated diphenylethers, partially debrominated PBDE congeners and polybrominated dibenzofuran. The UV-resistant bacterial strains isolated that could utilize BDE-209 as a sole carbon source included Stenotrophomonas sp., Pseudomonas sp., and Microbacterium sp. These strains encoded important functional genes such as dioxygenase and reductive dehalogenases. Continuous UV irradiation during the NBB process affected various biochemical oxidative reactions during PBDEs biodegradation. Simultaneous photolysis and biodegradation in the NBB system described reduces operational time, energy, expense, and maintenance-demands required for the remediation of BDE-209 when compared to sequential UV-biodegradation process or to biodegradation alone.

Natural organic matter does not diminish the mammalian bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic and persistent organic pollutant found in soils and sediments. It has been linked to several adverse health outcomes in humans and wildlife, including suppression of the immune system. TCDD is strongly sorbed to soils/sediments due to its extremely low water solubility. Presently, the bioavailability of soil/sediment-sorbed TCDD to mammals is not completely understood. Our previous studies demonstrated that TCDD adsorbed to representative inorganic geosorbents (i.e. porous silica and smectite clay) exhibited the same bioavailability to mice as TCDD dissolved in corn oil, whereas sequestration by activated carbons eliminated TCDD bioavailability. In this study, we evaluated the effects of amorphous natural organic matter (NOM), primarily in the form of aquatic humic and fulvic acids, on the mouse bioavailability of TCDD. An aqueous suspension of TCDD mixed with NOM was administered to mice via oral gavage. The relative bioavailability of TCDD was assessed by two sensitive aryl hydrocarbon receptor-mediated responses in mice: 1) hepatic induction of cyp1A1 mRNA; and 2) suppression of immunoglobulin M (IgM) antibody-forming cell (AFC) response which is an indicator of immunotoxicity. Hepatic induction of cyp1A1 mRNA and suppression of IgM AFC induced by TCDD were similar in the NOM-sorbed form and dissolved in corn oil, revealing no loss of bioavailability when associated with NOM. Hence, NOM-associated TCDD is as capable of suppressing humoral immunity in mice as TCDD dissolved in corn oil, indicating that NOM-sorbed TCDD is likely to fully retain its bioavailability to mammals and, by inference, humans.

Uptake of cephalexin by lettuce, celery, and radish from water.

The introduction of pharmaceuticals into agricultural lands from the application of biosolids and animal manure, and irrigation with treated wastewater has led to concern for animal and human health after the ingestion of pharmaceutical-tainted agricultural products. In this study, the uptake and accumulation of cephalexin, a commonly prescribed antibiotic, was compared in three common vegetables (lettuce, celery, and radish) grown in nutrient solution for 144 h. During the uptake experiments, cephalexin concentration in the nutrient solution decreased in the order of radish > celery > lettuce, while the accumulation of cephalexin in vegetable roots followed the rank of lettuce > celery > radish. The accumulation of cephalexin was below the limit of detection in radish roots. No accumulation of cephalexin was observed in the shoots of all three vegetables. The behaviors of cephalexin in vivo were further elucidated using in vitro measurements of cephalexin sorption by vegetable roots and transformation in plant enzyme extracts. The affinity of cephalexin to lettuce > celery > radish roots, and the respective sorption coefficients of 687, 303, and 161 mL g-1, coupled to the transformation of cephalexin in root enzyme extracts with estimated reaction rate constants of 0.020, 0.027 and 0.024 hr-1 for lettuce, celery and radish, could help elucidate the accumulation observed in the in vivo experiments. Overall, sorption by plant roots (affinity) and reaction with plant enzymes could collectively influence the uptake and accumulation of cephalexin in vegetables.

Synthesis and evaluation of Fe3O4-impregnated activated carbon for dioxin removal.

Polychlorinated dibenzo-p-dioxins and -furans (PCDD/PCDFs) are highly toxic organic pollutants in soils and sediments which persist over timescales that extend from decades to centuries. There is a growing need to develop effective technologies for remediating PCDD/Fs-contaminated soils and sediments to protect human and ecosystem health. The use of sorbent amendments to sequester PCDD/Fs has emerged as one promising technology. A synthesis method is described here to create a magnetic activated carbon composite (AC-Fe3O4) for dioxin removal and sampling that could be recovered from soils using magnetic separation. Six AC-Fe3O4 composites were evaluated (five granular ACs (GACs) and one fine-textured powder AC(PAC)) for their magnetization and ability to sequester dibenzo-p-dioxin (DD). Both GAC/PAC and GAC/PAC-Fe3O4 composites effectively removed DD from aqueous solution. The sorption affinity of DD for GAC-Fe3O4 was slightly reduced compared to GAC alone, which is attributed to the blocking of sorption sites. The magnetization of a GAC-Fe3O4 composite reached 5.38 emu/g based on SQUID results, allowing the adsorbent to be easily separated from aqueous solution using an external magnetic field. Similarly, a fine-textured PAC-Fe3O4 composite was synthesized with a magnetization of 9.3 emu/g.

Impact of biochar amendment on the uptake, fate and bioavailability of pharmaceuticals in soil-radish systems.

Crops grown in soils receiving wastewaters, biosolids, or manures can accumulate pharmaceuticals in edible parts, raising concerns over potential human exposure to multiple pharmaceuticals. Nonetheless, viable mitigation options for minimizing plant uptake of pharmaceuticals are limited. This study evaluated how biochar amendment could influence the uptake of 15 pharmaceuticals by radish (Raphanus sativus) grown in a sandy loam at two amendment rates (0.1 and 1% w/w). Comparing with that in the unamended soil, the accumulation of acetaminophen, carbamazepine, sulfadiazine, sulfamethoxazole, lamotrigine, carbadox, trimethoprim, oxytetracycline, tylosin, estrone, and triclosan in radish grown in the soil amended with 1.0% of biochar was significantly decreased by 33.3-83.0%. However, the concentration of lincomycin in radish was increased by 36.7-48.2% in the soil amended with 1% biochar. While the soil amended with 1.0% of biochar had increased sorption of all 15 pharmaceuticals, the persistence of 7 pharmaceuticals in the soil were prolonged, including caffeine, sulfadiazine, sulfamethoxazole, lincomycin, estrone, 17 ß-estradiol and triclosan. The reduced plant uptake of pharmaceuticals was mainly due to their lowered concentrations in pore water by the presence of biochar. Overall, the estimated daily intake data suggest that biochar amendment could potentially decrease total human exposure to a mixture of pharmaceuticals.

Characterization of a Sequential UV Photolysis-Biodegradation Process for Treatment of Decabrominated Diphenyl Ethers in Sorbent/Water Systems.

Decabrominated diphenyl ether (BDE-209) is a primary component of the brominated flame retardants used in a variety of industrial and domestic applications. BDE-209 bioaccumulates in aquatic organisms and has been identified as an emerging contaminant that threatens human and ecosystem health. Sequential photolysis-microbial biodegradation processes were utilized here to treat BDE-209 in clay- or soil-water slurries. The removal efficiency of BDE-209 in the clay-water slurries was high; i.e., 96.5%, while that in the soil-water slurries was minimal. In the clay-water slurries the first order rate constants for the UV photolysis and biodegradation of BDE-209 were 0.017 1/day and 0.026 1/day, respectively. UV wavelength and intensity strongly influenced the BDE-209 photolysis and the subsequent biodegradation of photolytic products. Facultative chemotrophic bacteria, including Acidovorax spp., Pseudomonas spp., Novosphingobium spp. and Sphingomonas spp., were the dominant members of the bacterial community (about 71%) at the beginning of the biodegradation; many of these organisms have previously been shown to biodegrade BDE-209 and other polybrominated diphenyl ether (PBDE) congeners. The Achromobacter sp. that were isolated (NH-2; NH-4; NH-6) were especially effective during the BDE-209 degradation. These results indicated the effectiveness of the sequential UV photolysis and biodegradation for treating certain BDE-209-contaminated solids; e.g., clays; in bioreactors containing such solids as aqueous slurries. Achieving a similar treatment effectiveness for more heterogeneous solids containing natural organic matter, e.g., surface solids, appears to be significantly more difficult. Further investigations are needed in order to understand the great difference between the clay-water or soil-water slurries.

Bioavailability of clay-adsorbed dioxin to Sphingomonas wittichii RW1 and its associated genome-wide shifts in gene expression.

Polychlorinated dibenzo-p-dioxins and dibenzofurans are a group of chemically-related pollutants categorically known as dioxins. Some of their chlorinated congeners are among the most hazardous pollutants that persist in the environment. This persistence is due in part to the limited number of bacteria capable of metabolizing these compounds, but also to their limited bioavailability in soil. We used Sphingomonas wittichii strain RW1 (RW1), one of the few strains able to grow on dioxin, to characterize its ability to respond to and degrade clay-bound dioxin. We found that RW1 grew on and completely degraded dibenzo-p-dioxin (DD) intercalated into the smectite clay saponite (SAP). To characterize the effects of DD sorption on RW1 gene expression, we compared transcriptomes of RW1 grown with either free crystalline DD or DD intercalated clay, i.e. sandwiched between the clay interlayers (DDSAP). Free crystalline DD appeared to cause greater expression of toxicity and stress related functions. Genes coding for heat shock proteins, chaperones, as well as genes involved in DNA repair, and efflux were up-regulated during growth on crystalline dioxin compared to growth on intercalated dioxin. In contrast, growth on intercalated dioxin up-regulated genes that might be important in recognition and uptake mechanisms, as well as surface interaction/attachment/biofilm formation such as extracellular solute-binding protein and LuxR. These differences in gene expression may reflect the underlying adaptive mechanisms by which RW1 cells sense and deploy pathways to access dioxin intercalated into clay. These data show that intercalated DD remains bioavailable to the degrading bacterium with implications for bioremediation alternatives.

Mechanistic study on uptake and transport of pharmaceuticals in lettuce from water.

The dissemination of pharmaceuticals in agroecosystems originating from land application of animal manure/sewage sludge and irrigation with treated wastewater in agricultural production has raised concern about the accumulation of pharmaceuticals in food products. The pathways of pharmaceutical entries via plant roots, transport to upper fractions, and the factors influencing these processes have yet been systematically elucidated, thus impeding the development of effective measures to mitigate pharmaceutical contamination in food crops. In this study, lettuce uptake of thirteen commonly used pharmaceuticals was investigated using a hydroponic experimental setting. Pharmaceutical sorption by lettuce roots was measured in order to evaluate the influence on pharmaceutical transport from roots to shoots. Small-sized pharmaceuticals e.g., caffeine and carbamazepine with molecular weight (MW) <300 g mol-1 and a low affinity to lettuce roots (sorption coefficient Kp < 0.05 L g-1) manifested substantial transport to shoots. Small-sized molecules lamotrigine and trimethoprim had a relatively strong affinity to lettuce roots (Kp > 12.0 L g-1) and demonstrated a reduced transport to shoots. Large-sized pharmaceuticals (e.g. MW >400 g mol-1) including lincomycin, monensin sodium, and tylosin could be excluded from cell membranes, resulting in the predominant accumulation in lettuce roots. Large-sized oxytetracycline existed as zwitterionic species that could slowly enter lettuce roots; however, the relatively strong interaction with lettuce roots limits its transport to shoots. The mass balance analysis revealed that acetaminophen, ß-estradiol, carbadox, estrone and triclosan were readily metabolized in lettuce with >90% loss during 144-h exposure period. A scheme was proposed to describe pharmaceutical uptake and transport in plant, which could reasonably elucidate many literature-reported results. Molecular size, reactivity and ionic speciation of pharmaceuticals, as well as plant physiology, collectively determine their uptake, transport and accumulation in plants.

Long-term sorption of lincomycin to biochars: The intertwined roles of pore diffusion and dissolved organic carbon.

Sequestration of anthropogenic antibiotics by biochars from waters may be a promising strategy to minimize environmental and human health risks of antibiotic resistance. This study investigated the long-term sequestration of lincomycin by 17 slow-pyrolysis biochars using batch sorption experiments during 365 days. Sorption kinetics were well fitted to the Weber-Morris intraparticle diffusion model for all tested biochars with the intraparticle diffusion rate constant (kid) of 25.3-166 µg g-1 day-0.5 and intercept constant (Cid) of 39.0-339 µg g-1, suggesting that the sorption kinetics were controlled by fast initial sorption and slow pore diffusion. The quasi-equilibrium sorption isotherms became more nonlinear with increasing equilibration time at 1, 7, 30, and 365 days, likely due to increasing abundance of heterogeneous sorption sites in biochars over time. Intriguingly, low-temperature (300 °C) and high-temperature (600 °C) biochars had faster sorption kinetics than intermediate-temperature (400-500 °C) biochars at the long term, which was attributed to greater specific surface area and pore volume of high-temperature biochars and the substantial and continuous release of dissolved organic carbon (DOC) from low-temperature biochars, respectively. DOC release enhanced lincomycin sorption by decreasing biochar particle size and/or increasing the accessibility of sorption sites and pores initially blocked by DOC. Additionally, a large fraction (>75%) of sorbed lincomycin in biochars after a 240-day equilibration could not be extracted by the acetonitrile/methanol extractant. The strong sorption and low extraction recovery demonstrated the great potential of biochars as soil amendments for long-term sequestration of antibiotics in-situ.

Antibiotic resistance genes and bacterial communities in cornfield and pasture soils receiving swine and dairy manures.

Land application of animal manure could change the profiles of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and bacterial communities in receiving soils. Using high-throughput real-time quantitative PCR and 16S rRNA amplicon sequencing techniques, this study investigated the ARGs and bacterial communities in field soils under various crop (corn and pasture) and manure (swine and dairy) managements, which were compared with those of two non-manured reference soils from adjacent golf course and grassland. In total 89 unique ARG subtypes were found in the soil samples and they conferred resistance via efflux pump, cellular protection and antibiotic deactivation. Compared to the ARGs in the golf course and grassland soils (28 and 34 subtypes respectively), manured soils generally had greater ARG diversity (36-55 subtypes). Cornfield soil frequently receiving raw swine manure had the greatest ARG abundance. The short-term (one week) application of composted and liquid swine manures increased the diversity and total abundance of ARGs in cornfield soils. Intriguingly the composted swine manure only marginally increased the total abundance of ARGs, but substantially increased the number of ARG subtypes in the cornfield soils. The network analysis revealed three major network modules in the co-occurrence patterns of ARG subtypes, and the hubs of these major modules (intl1-1, vanC, and pncA) may be candidates for selecting indicator genes for surveillance of ARGs in manured soils. The network analyses between ARGs and bacteria taxa revealed the potential host bacteria for the detected ARGs (e.g., aminoglycoside resistance gene aacC4 may be mainly carried by Acidobacteriaceae). Overall, this study highlighted the potentially varying impact of various manure management on antibiotic resistome and microbiome in cornfield and pasture soils.

Insight into the distribution of pharmaceuticals in soil-water-plant systems.

Pharmaceuticals in agricultural soils originating from irrigation with treated wastewater and land-applied biosolids can enter field crops. However, little is known about the role of pore water in plant uptake of pharmaceuticals from soils. In this study, the fate, uptake and distribution of fifteen commonly used pharmaceuticals in soil-water-radish systems were investigated to examine the relationship between the accumulation and their physicochemical processes in soils. The results indicate that the distribution of pharmaceuticals between soil and pore water, as well as their biodegradation, combined to govern the bioavailability of pharmaceuticals to plant uptake. Fourteen out of 15 pharmaceuticals could enter radish tissues in which the accumulation ranged from 2.1 to 14080 ng/g. Comparison of bioconcentration factors (BCFs) on the basis of pharmaceutical concentration in bulk soil vs. in pore water implies that pharmaceuticals present in soil pore water are the major bioavailable fractions to plant uptake. The pore water-based BCFs exhibited a positive linear relationship with log Dow for the pharmaceuticals with >90% as neutral species in soil pore water, while such relationship was not observed between bulk soil-based BCFs and log Dow mainly due to sorption by soil. Other than hydrophobicity, the dissociation of ionizable pharmaceuticals in the soil pore water and (or) root cells may lead to the "ion-trap" effects and thus influence the uptake and translocation process. The large molecular-size pharmaceuticals (e.g., tylosin) manifested a minimum uptake due plausibly to the limited permeability of cell membranes.

Activated carbons of varying pore structure eliminate the bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin to a mammalian (mouse) model.

The use of activated carbon (AC) as an in situ sorbent amendment to sequester polychlorinated-dibenzo-p-dioxins and furans (PCDD/Fs) present in contaminated soils and sediments has recently gained attention as a novel remedial approach. This remedy could be implemented at much lower cost while minimizing habitat destruction as compared to traditional remediation technologies that rely on dredging/excavation and landfilling. Several prior studies have demonstrated the ability of AC amendments to reduce pore water concentrations and hence bioaccumulation of PCDD/Fs in invertebrate species. However, our recent study was the first to show that AC had the ability to sequester 2,3,7,8­tetrachlorodibenzo­p­dioxin (TCDD) in a form that eliminated bioavailability to a mammalian (mouse) model. Here we show that three commercially available ACs, representing a wide range of pore size distributions, were equally effective in eliminating the bioavailability of TCDD based upon two sensitive bioassays, hepatic induction of cyp1A1 mRNA and immunoglobulin M antibody-forming cell response. These results provide direct evidence that a wide range of structurally diverse commercially available ACs may be suitable for use as in situ sorbent amendments to provide a cost-effective remedy for PCDD/F contaminated soils and sediments. Potentially, adaption of this technology would minimize habitat destruction and be protective of ecosystem and human health.

Potential metabolism of pharmaceuticals in radish: Comparison of in vivo and in vitro exposure.

Metabolism of pharmaceuticals in plants is important to evaluate their fate and accumulation in vegetables, and subsequently the risks to human health. However, limited knowledge is available to evaluate metabolism of pharmaceuticals in plants due to the lack of appropriate research approaches. In this study, radish was selected as a model plant to investigate metabolism of pharmaceuticals in intact plants (in vivo) growing in hydroponic solution and in plant tissue enzyme extracts (in vitro). For caffeine, six phase-I demethylation metabolites identified in the intact radish plant were also found in the plant enzyme extracts. After 7 days of in vivo exposure, the amount of the identified metabolites was about 5.4 times greater than the parent compound caffeine in radish roots. Furthermore, the metabolism potential of fifteen pharmaceuticals in radish was evaluated on the basis of mass balance. After 7 days of hydroponic exposure, oxytetracycline, trimethoprim, carbamazepine, lincomycin, monensin and tylosin manifested relatively less extent of metabolism with the mass recoveries ranging from 52.3 to 78.2%. In contrast, 17 ß-estradiol, sulfamethoxazole, sulfadiazine, estrone, triclosan, acetaminophen, caffeine, carbadox and lamotrigine underwent extensive metabolism with only 3.0 to 32.1% of the parent compound recovered. In the in vitro system, 17 ß-estradiol, estrone, triclosan, oxytetracycline, acetaminophen, sulfadiazine and sulfamethoxazole were readily metabolized in radish root enzyme extracts with 1.8 to 34.0% remaining after 96-h exposure. While in the leaf enzyme extracts, only triclosan was rapidly metabolized with 49.2% remaining, and others pharmaceuticals were ≥60%, indicating that the varying extents of metabolism occurred in different plant parts. This study highlights the importance of pharmaceutical metabolism in plants, and suggests that plant tissue enzyme extracts could serve as an alternative tool to assess pharmaceutical metabolism in plants.

Bioavailability of tetracycline to antibiotic resistant Escherichia coli in water-clay systems.

Tetracyclines are a class of antimicrobials frequently found in the environment, and have promoted the proliferation of antibiotic resistance. An unanswered research question is whether tetracycline sorbed to soils is still bioavailable to bacteria and exerts selective pressure on the bacterial community for the development of antibiotic resistance. In this study, bioreporter E. coli MC4100/pTGM strain was used to probe the bioavailability of tetracycline sorbed by smectite clay, a class of common soil minerals. Batch sorption experiments were conducted to prepare clay samples with a wide range of sorbed tetracycline concentration. The bioreporter was incubated with tetracycline-sorbed clay at different clay/solution ratios and water contents, as well as using dialysis tubings to prevent the direct contact between bacterial cells and clay particles. The expression of antibiotic resistance genes from the bioreporter was measured using a flow cytometer as a measurement of bioavailability/selective pressure. The direct contact of bioreporter cells to clay surfaces represented an important pathway facilitating bacterial access to clay-sorbed tetracycline. In clay-water suspensions, reducing solution volume rendered more bacteria to attach to clay surfaces enhancing the bioavailability of clay-sorbed tetracycline. The strong fluorescence emission from bioreporter cells on clay surfaces indicated that clay-sorbed tetracycline was still bioavailable to bacteria. The formation of biofilms on clay surfaces could increase bacterial access to clay-sorbed tetracycline. In addition, desorption of loosely sorbed tetracycline into bulk solution contributed to bacterial exposure and activation of the antibiotic resistance genes. Tetracycline sorbed by soil geosorbents could exert selective pressure on the surrounding microbial communities via bacterial exposure to tetracycline in solution from desorption and to the geosorbent-sorbed tetracycline as well.

Metabolic Demethylation and Oxidation of Caffeine during Uptake by Lettuce.

Pharmaceuticals can be metabolized after being taken up by plants. The metabolites could manifest similar or equivalent bioactivity to the parent compound, promoting the critical need to understand the metabolism in plants. Caffeine has been frequently detected in agriculture produce; however, little attention is given to its metabolites in vegetables. This study examined uptake and metabolism of caffeine in lettuce in a hydroponic system. Caffeine and its metabolites in aqueous solution and lettuce were identified and quantified using a liquid chromatography coupled to a QTrap tandem mass spectrometry instrument. After 144 h, over 50% of applied caffeine dissipated in the hydroponic lettuce system, and eight caffeine metabolites were identified primarily in the shoots. Caffeine underwent demethylation reactions, which were confirmed with authentic standards, and the total amount accounted for 20% of the initially applied caffeine. Other metabolism pathways included oxidation and hydroxylation, and the amount of metabolites increased over uptake time.

TCDD administered on activated carbon eliminates bioavailability and subsequent shifts to a key murine gut commensal.

Activated carbon (AC) is an increasingly attractive remediation alternative for the sequestration of dioxins at contaminated sites globally. However, the potential for AC to reduce the bioavailability of dioxins in mammals and the residing gut microbiota has received less attention. This question was partially answered in a recent study examining 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced hallmark toxic responses in mice administered with TCDD sequestered by AC or freely available in corn oil by oral gavage. Results from that study support the use of AC to significantly reduce the bioavailability of TCDD to the host. Herein, we examined the bioavailability of TCDD sequestered to AC on a key murine gut commensal and the influence of AC on the community structure of the gut microbiota. The analysis included qPCR to quantify the expression of segmented filamentous bacteria (SFB) in the mouse ileum, which has responded to TCDD-induced host toxicity in previous studies and community structure via sequencing the 16S ribosomal RNA (rRNA) gene. The expression of SFB 16S rRNA gene and functional genes significantly increased with TCDD administered with corn oil vehicle. Such a response was absent when TCDD was sequestered by AC. In addition, AC appeared to have a minimal influence on murine gut community structure and diversity, affecting only the relative abundance of Lactobacillaceae and two other groups. Results of this study further support the remedial use of AC for eliminating bioavailability of TCDD to host and subsequent influence on the gut microbiome.