1,4-Dioxane (dioxane) is a groundwater contaminant of emerging concern for which bioremediation may be a promising strategy. Several bacterial strains can metabolize dioxane or degrade it cometabolically. However, the molecular basis of dioxane biodegradation is only partially understood, and the gene coding for dioxane/tetrahydrofuran (THF) monooxygenase in Pseudonocardia dioxanivorans CB1190 is the only well-characterized catabolic gene. Here, we identify a novel group-6 propane monooxygenase gene cluster (prmABCD) in Mycobacterium dioxanotrophicus PH-06, which is a bacterium with superior dioxane degradation kinetics compared with CB1190. Whole genome sequencing of PH-06 revealed the existence of a single soluble di-iron monooxygenase (SDIMO). RNA sequencing and reverse transcription quantitative PCR (RT-qPCR) subsequently confirmed that all four components of this gene cluster are upregulated when PH-06 is grown on dioxane compared with growth on acetate or glucose as negative controls. This first characterization of a group-6 SDIMO associated with dioxane biodegradation suggests that dioxane-degrading genes may be more diverse than previously appreciated. A primer/probe set designed to target the large hydroxylase subunit of this gene cluster exhibited high selectivity (no false positives) and high sensitivity (detection limit = 3000–4000 gene copies/mL culture), which may be useful to help assess the presence of dioxane degraders at contaminated sites and minimize false negatives.

Bacteriophages are widely recognized for their importance in microbial ecology and bacterial control. However, little is known about how phage polyvalence (i.e., broad host range) affects bacterial suppression and interspecies competition in environments harboring enteric pathogens and soil bacteria. Here we compare the efficacy of polyvalent phage PEf1 versus coliphage T4 in suppressing a model enteric bacterium (E. coli K-12) in mixtures with soil bacteria (Pseudomonas putida F1 and Bacillus subtilis 168). Although T4 was more effective than PEf1 in infecting E. coli K-12 in pure cultures, PEf1 was 20-fold more effective in suppressing E. coli under simulated multispecies biofilm conditions because polyvalence enhanced PEf1 propagation in P. putida. In contrast, soil bacteria do not propagate coliphages and hindered T4 diffusion through the biofilm. Similar tests were also conducted under planktonic conditions to discern how interspecies competition contributes to E. coli suppression without the confounding effects of restricted phage diffusion. Significant synergistic suppression was observed by the combined effects of phages plus competing bacteria. T4 was slightly more effective in suppressing E. coli in these planktonic mixed cultures, even though PEf1 reached higher concentrations by reproducing also in P. putida (7.2 ± 0.4 vs 6.0 ± 1.0 log10PFU/mL). Apparently, enhanced suppression by higher PEf1 propagation was offset by P. putida lysis, which decreased stress from interspecies competition relative to incubations with T4. In similar planktonic tests with more competing soil bacteria species, P. putida lysis was less critical in mitigating interspecies competition and PEf1 eliminated E. coli faster than T4 (36 vs 42 h). Overall, this study shows that polyvalent phages can propagate in soil bacteria and significantly enhance suppression of co-occurring enteric species.

Bacteriophage-based microbial control could help address a growing need to attenuate the proliferation of antibiotic-resistant bacteria (ARB) in wastewater treatment plants (WWTPs). However, the infectivity of commonly isolated narrow-host-range phages decreases quickly upon addition to activated sludge (i.e., plaque-forming units had a half-life of 0.63 h). Here, we show that polyvalent (broad-host-range) phages proliferate and thrive in activated sludge microcosms, especially when added along with their production hosts. Polyvalent phage cocktails (PER01 and PER02) were significantly more effective than narrow-host-range coliphage cocktails (MER01 and MER02) in suppressing a model ARB [β-lactam-resistant Escherichia coli NDM-1, initially present at 6.2 ± 0.1 log10 colony-forming units (CFU)/mL]. After 5 days, the NDM-1 concentration significantly decreased to 3.8 ± 0.2 log10 CFU/mL in the presence of the polyvalent phage cocktail, compared to 4.7 ± 0.3 log10 CFU/mL for the coliphage cocktail treatment. Because of the presence of alternative hosts, polyvalent phages reached greater densities, which increased the probability of ARB infection. The fraction of surviving E. coli harboring the blaNDM-1 resistance gene was also significantly lower for the polyvalent phage cocktail treatment (0.57 ± 0.07) than for the control (0.74 ± 0.08). Therefore, polyvalent phages safely produced with nonpathogenic hosts could offer a novel approach to controlling problematic ARB in WWTPs and mitigating the propagation and discharge of associated resistance genes to the environment.

Biofilms may shelter pathogenic or other problematic microorganisms that are difficult to eradicate due to hindered penetration of antimicrobial chemicals. Here, we demonstrate the potential for efficient bacterial suppression using polyvalent (broad host-range) phages attached to magnetic colloidal nanoparticle clusters (CNCs) that facilitate biofilm penetration under a relatively small magnetic field (660 gauss). The polyvalent phage PEL1 (Podoviridae family) was immobilized onto Fe3O4-based magnetic CNCs that had been coated with chitosan (and thus functionalized with amino groups). This facilitated conjugation with phages via covalent bonding (i.e., amide linkages) and enabled phage loading, which reached (5.2 ± 0.7) × 103 centers of infection per 1 μg of chitosan-coated CNCs (CS-Fe3O4). The plaque formation capability of PEL1–CS-Fe3O4 on Pseudomonas aeruginosa PA01 and Escherichia coli C3000 lawns was significantly higher than that of phages conjugated with similar CNCs that had been functionalized with carboxyl groups (99.1% vs. 3.2% Petri dish area of infection). In newly established biofilms formed from these two species on a glass surface, PEL1–CS-Fe3O4 removed 88.7 ± 2.8% of the biofilm coverage area after 6 h of treatment. Overall, this conjugation approach could extend the application of phages for microbial control by enhancing their delivery to relatively inaccessible locations within biofilms.

A major challenge for photocatalytic water purification with TiO2 is the strong inhibitory effect of natural organic matter (NOM), which can scavenge photogenerated holes and radicals and occlude ROS generation sites upon adsorption. This study shows that phosphate counteracts the inhibitory effect of humic acids (HA) by decreasing HA adsorption and mitigating electron–hole recombination. As a measure of the inhibitory effect of HA, the ratios of first-order reaction rate constants between photocatalytic phenol degradation in the absence versus presence of HA were calculated. This ratio was very high, up to 5.72 at 30 mg/L HA and pH 4.8 without phosphate, but was decreased to 0.76 (5 mg/L HA, pH 8.4) with 2 mM phosphate. The latter ratio indicates a surprising favorable effect of HA on TiO2 photocatalysis. FTIR analyses suggest that this favorable effect is likely due to a change in the conformation of adsorbed HA, from a multiligand exchange arrangement to a complexation predominantly between COOH groups in HA and the TiO2 surface in the presence of phosphate. This configuration can reduce hole consumption and facilitate electron transfer to O2 by the adsorbed HA (indicated by linear sweep voltammetry), which mitigates electron–hole recombination and enhances contaminant degradation. A decrease in HA surface adsorption and hole scavenging (the predominant inhibitory mechanisms of HA) by phosphate (2 mM) was indicated by a 50% decrease in the photocatalytic degradation rate of HA and 80% decrease in the decay rate coefficient of interfacial-related photooxidation in photocurrent transients. These results, which were validated with other compounds (FFA and cimetidine), indicate that anchoring phosphate - or anions that exert similar effects on the TiO2 surface - might be a feasible strategy to counteract the inhibitory effect of NOM during photocatalytic water treatment.

Responsible development of nanotechnology calls for improved understanding of how nanomaterial surface energy and reactivity affect potential toxicity. Here, we challenge the paradigm that cytotoxicity increases with nanoparticle reactivity. Higher-surface-energy {001}-faceted CdS nanorods (CdS-H) were less toxic to Saccharomyces cerevisiae than lower-energy ({101}-faceted) nanorods (CdS-L) of similar morphology, aggregate size, and charge. CdS-H adsorbed to the yeast’s cell wall to a greater extent than CdS-L, which decreased endocytosis and cytotoxicity. Higher uptake of CdS-L decreased cell viability and increased endoplasmatic reticulum stress despite lower release of toxic Cd2+ ions. Higher toxicity of CdS-L was confirmed with five different unicellular microorganisms. Overall, higher-energy nanocrystals may exhibit greater propensity to adsorb to or react with biological protective barriers and/or background constituents, which passivates their reactivity and reduces their bioavailability and cytotoxicity.

Pyrolysis of contaminated soils at 420 °C converted recalcitrant heavy hydrocarbons into “char” (a carbonaceous material similar to petroleum coke) and enhanced soil fertility. Pyrolytic treatment reduced total petroleum hydrocarbons (TPH) to below regulatory standards (typically <1% by weight) within 3 h using only 40–60% of the energy required for incineration at 600–1200 °C. Formation of polycyclic aromatic hydrocarbons (PAHs) was not observed, with post-pyrolysis levels well below applicable standards. Plant growth studies showed a higher biomass production of Arabidopsis thaliana and Lactuca sativa (Simpson black-seeded lettuce) (80–900% heavier) in pyrolyzed soils than in contaminated or incinerated soils. Elemental analysis showed that pyrolyzed soils contained more carbon than incinerated soils (1.4–3.2% versus 0.3–0.4%). The stark color differences between pyrolyzed and incinerated soils suggest that the carbonaceous material produced via pyrolysis was dispersed in the form of a layer coating the soil particles. Overall, these results suggest that soil pyrolysis could be a viable thermal treatment to quickly remediate soils impacted by weathered oil while improving soil fertility, potentially enhancing revegetation.

Hydrocarbon souring represents a significant safety and corrosion challenge to the oil and gas industry. H2S may originate from geochemical or biogenic sources, although its source is rarely discerned. Biocides are sometimes utilized during well operations to prevent or inhibit H2S generation. Here we develop a regional temperature map showing that downhole temperatures in Bakken reservoir wells equal or exceed the upper known temperature limit for microbial life. Attempts to extract microbial DNA from produced water yielded little to no detectable quantities. Stable isotope analysis yielded 34Sδ values from 4.4 to 9.8‰, suggesting souring had a geochemical origin. Under Bakken reservoir conditions, anhydrite can react with hydrocarbons to form H2S. Anhydrite present near the sour areas studied could be the underlying geochemical source creating this H2S. In cases of geochemical souring, reevaluation of the need for biocide addition may provide significant reductions in both operational costs and overall environmental footprint.

Seeking economic growth and job creation to tackle the nation’s extreme poverty, the Nicaraguan government awarded a concession to build an interoceanic canal and associated projects to a recently formed Hong Kong based company with no track record or related expertise. This concession was awarded without a bidding process and in advance of any feasibility, socio-economic or environmental impact assessments; construction has begun without this information. The 278 km long interoceanic canal project may result in significant environmental and social impairments. Of particular concern are damage to Lake Cocibolca, a unique freshwater tropical lake and Central America’s main freshwater reservoir; damage to regional biodiversity and ecosystems; and socio-economic impacts. Concerned about the possibly irreparable damage to the environment and to native communities, conservationists and the scientific community at large are urging the Nicaraguan government to devise and reveal an action plan to address and mitigate the possible negative repercussions of this interoceanic canal and associated projects. Critical research needs for preparation of a comprehensive benefit-cost analysis for this megaproject are presented.

Although silver nanoparticles (AgNPs) are used as antimicrobial agents in a wide variety of commercial products, sublethal exposure can counterproductively promote the development of biofilms. We observed by fluorescence microscopy denser biofilm growth with mixed cultures from a wastewater treatment plant after exposure to 21.6 μg/L 10 nm AgNPs. To further understand biofilm promotion mechanisms, experiments were conducted with a pure culture of Pseudomonas aeruginosa PAO1. Sublethal exposure of PAO1 to AgNPs (10.8 and 21.6 μg/L) also enhanced biofilm development and upregulated quorum sensing, lipopolysaccharide biosynthesis, and antibiotic resistance (efflux pump) genes. An increase in the sugar and protein contents of the PAO1 biofilm matrix (by 55 ± 3 and 114 ± 32%, respectively, relative to unexposed controls) corroborated the transcriptional upregulation of PAO1 biofilm-related genes. Enhanced biofilm development by exposure to low AgNP concentrations might accelerate biofouling and biocorrosion and harbor pathogens that pose a risk to public health.

1,4-Dioxane (dioxane) is relatively recalcitrant to biodegradation, and its physicochemical properties preclude effective removal from contaminated groundwater by volatilization or adsorption. Through this microcosm study, we assessed the biodegradation potential of dioxane for three sites in California. Groundwater and sediment samples were collected at various locations at each site, including the presumed source zone, middle and leading edge of the plume. A total of 16 monitoring wells were sampled to prepare the microcosms. Biodegradation of dioxane was observed in 12 of 16 microcosms mimicking natural attenuation within 28 weeks. Rates varied from as high as 3,449 ± 459 µg/L/week in source-zone microcosms to a low of 0.3 ± 0.1 µg/L/week in microcosms with trace level of dioxane (<10 µg/L as initial concentration). The microcosms were spiked with 14C-labeled dioxane to assess the fate of dioxane. Biological oxidizer-liquid scintillation analysis of bound residue infers that 14C-dioxane was assimilated into cell material only in microcosms exhibiting significant dioxane biodegradation. Mineralization was also observed per 14CO2 recovery (up to 44 % of the amount degraded in 28 weeks of incubation). Degradation and mineralization activity significantly decreased with increasing distance from the contaminant source area (p < 0.05), possibly due to less acclimation. Furthermore, both respiked and repeated microcosms prepared with source-zone samples from Site 1 confirmed relatively rapid dioxane degradation (i.e., 100 % removal by 20 weeks). These results show that indigenous microorganisms capable of degrading dioxane are present at these three sites, and suggest that monitored natural attenuation should be considered as a remedial response.

Microorganisms can cause detrimental effects in shale gas production, such as reservoir souring, plugging, equipment corrosion, and a decrease in hydrocarbon production volume and quality, thus representing a multi-billion-dollar problem. Prefracturing fluids, drilling mud, and impoundment water likely introduce deleterious microorganisms into shale gas reservoirs. Conditions within the reservoir generally select for halotolerant anaerobic microorganisms. Microbial abundance and diversity in flowback waters decrease shortly after hydraulic fracturing, with Clostridia, a class that includes spore-forming microorganisms, becoming dominant. The rapid microbial community successions observed suggest biocides are not fully effective, and more targeted treatment strategies are needed. At the impoundment level, microbial control strategies should consider biocide rotation, seasonal loading adjustments, and biocide pulse dosing. In shale plays where souring is common, stable 34S/32S isotope analysis to identify abiotic H2S is recommended to evaluate the merits of biocide application in treating reservoir souring. Overall, an improved understanding of the microbial ecology of shale gas reservoirs is needed to optimize microbial control, maximize well productivity, and reduce environmental and financial burdens associated with the ad hoc misuse and overuse of biocides.

1,4-Dioxane (dioxane) is a cocontaminant of emerging concern at thousands of sites impacted by chlorinated solvents, and there is an urgent need to assess site-specific dioxane biodegradation capabilities. In this study, a primer/probe set was developed to target bacterial genes encoding the large hydroxylase subunit of a putative tetrahydrofuran/dioxane monooxygenase (an enzyme proposed to initiate dioxane catabolism), using TaqMan (5′-nuclease) chemistry. This effort relied on multiple-sequence alignment of the four thmA/dxmA genes available on the National Center for Biotechnology Information database. The probe targets conserved regions surrounding the active site, thus allowing detection of multiple dioxane degraders. Real-time polymerase chain reaction using reference strain genomic DNA demonstrated the high selectivity (no false positives) and sensitivity of this probe (7000–8000 copies/g of soil). Microcosm tests prepared with groundwater samples from 16 monitoring wells at five different dioxane-impacted sites showed that enrichment of this catabolic gene (up to 114-fold) was significantly correlated with the amount of dioxane degraded. A significant correlation was also found between biodegradation rates and the abundance of thmA/dxmA genes. In contrast, 16S rRNA gene copy numbers (a measure of total bacteria) were neither sensitive nor reliable indicators of dioxane biodegradation activity. Overall, these results suggest that this novel catabolic biomarker (thmA/dxmA) has great potential for the rapid assessment of the performance of natural attenuation or bioremediation of dioxane plumes.

The transformation of engineered nanomaterials in the environment can significantly affect their transport, fate, bioavailability, and toxicity. Little is known about the biotransformation potential of single-walled carbon nanotubes (SWNTs). In this study, we compared the enzymatic transformation of SWNTs and oxidized (carboxylated) SWNTs (O-SWNTs) using three ligninolytic enzymes: lignin peroxidase, manganese peroxidase (MnP), and laccase. Only MnP was capable of transforming SWNTs, as determined by Raman spectroscopy, near-infrared spectroscopy, and transmission electron microscopy. Interestingly, MnP degraded SWNTs but not O-SWNTs. The recalcitrance of O-SWNTs to enzymatic transformation is likely attributable to the binding of Mn2+ by their surface carboxyl groups at the enzyme binding site, which inhibits critical steps in the MnP catalytic cycle (i.e., Mn2+ oxidation and Mn3+ dissociation from the enzyme). Our results suggest that oxygen-containing surface functionalities do not necessarily facilitate the biodegradation of carbonaceous nanomaterials, as is commonly assumed.

The New Delhi metallo-β-lactamase (NDM-1) increases bacterial resistance to a broad range of antibiotics, and bacteria that produce it can cause infections that are very difficult to treat, thus posing great risks to human health. This paper addresses the occurrence of NDM-1 genes through different processes in wastewater treatment plants (WWTPs). NDM-1 genes prevailed through several treatment units (including disinfection by chlorination) in two WWTPs in northern China. Significant NDM-1 gene levels were present in the effluent discharged from both WWTPs (from 1316 ± 232 to 1431 ± 247 copies/mL, representing from 4.4 to 93.2%, respectively, of influent levels). NDM-1 genes were present at much higher concentrations in dewatered waste sludge that is applied to soils [(4.06 ± 0.98) × 107 to (6.21 ± 2.23) × 107 copies/g of dry weight], raising the possibility of propagation to indigenous bacteria. This concern was validated by a conjugation experiment with Haihe River sediment not harboring NDM-1 genes at detectable levels, where an NDM-1-positive Achromobacter sp. isolated from a WWTP transferred the NDM-1 gene to an indigenous Comamonas sp. The discharge of NDM-1 genes in the effluent and dewatered waste sludge from WWTPs (even at rates higher than influent values) underscores the need to better understand and mitigate their proliferation and propagation from WWTPs.

Manipulation of the organic coatings of nanoparticles such as quantum dots (QDs) to enhance specific applications may also affect their interaction and uptake by different organisms. In this study, poplar trees (Populus deltoides × nigra) were exposed hydroponically to 50-nM CdSe/CdZnS QDs coated with cationic polyethylenimine (PEI) (35.3 ± 6.6 nm) or poly(ethylene glycol) of anionic poly(acrylic acid) (PAA-EG) (19.5 ± 7.2 nm) to discern how coating charge affects nanoparticle uptake, translocation, and transformation within woody plants. Uptake of cationic PEI-QDs was 10 times faster despite their larger hydrodynamic size and higher extent of aggregation (17 times larger than PAA-EG-QDs after 11-day incubation in the hydroponic medium), possibly due to electrostatic attraction to the negatively charged root cell wall. QDs cores aggregated upon root uptake, and their translocation to poplar shoots (negligible for PAA-EG-QDs and 0.7 ng Cd/mg stem for PEI-QDs) was likely limited by the endodermis. After 2-day exposure, PEI and PAA-EG coatings were likely degraded from the internalized QDs inside the plant, leading to the aggregation of the metallic cores and a “red-shift” of fluorescence. The fluorescence of PEI-QD aggregates was stable inside the roots through the 11-day exposure period. In contrast, the PAA-EG-QD aggregates lost fluorescence inside the plant after 11 days probably due to destabilization of the coating, even though these QDs were stable in the hydroponic solution. Overall, these results highlight the importance of coating properties in the rate and extent to which nanoparticles are assimilated by plants and potentially introduced into food webs.

Ethanol-blended fuel releases usually stimulate methanogenesis in the subsurface, which could pose an explosion risk if methane accumulates in a confined space above the ground where ignitable conditions exist. Ethanol-derived methane may also increase the vapor intrusion potential of toxic fuel hydrocarbons by stimulating the depletion of oxygen by methanotrophs, and thus inhibiting aerobic biodegradation of hydrocarbon vapors. To assess these processes, a three-dimensional numerical vapor intrusion model was used to simulate the degradation, migration, and intrusion pathway of methane and benzene under different site conditions. Simulations show that methane is unlikely to build up to pose an explosion hazard (5% v/v) if diffusion is the only mass transport mechanism through the deeper vadose zone. However, if methanogenic activity near the source zone is sufficiently high to cause advective gas transport, then the methane indoor concentration may exceed the flammable threshold under simulated conditions. During subsurface migration, methane biodegradation could consume soil oxygen that would otherwise be available to support hydrocarbon degradation, and increase the vapor intrusion potential for benzene. Vapor intrusion would also be exacerbated if methanogenic activity results in sufficiently high pressure to cause advective gas transport in the unsaturated zone. Overall, our simulations show that current approaches to manage the vapor intrusion risk for conventional fuel released might need to be modified when dealing with some high ethanol blend fuel (i.e., E20 up to E95) releases.

The propagation of antibiotic resistance genes (ARGs) represents a global threat to both human health and food security. Assessment of ARG reservoirs and persistence is therefore critical for devising and evaluating strategies to mitigate ARG propagation. This study developed a novel, internal standard method to extract extracellular DNA (eDNA) and intracellular DNA (iDNA) from water and sediments, and applied it to determine the partitioning of ARGs in the Haihe River basin in China, which drains an area of intensive antibiotic use. The concentration of eDNA was higher than iDNA in sediment samples, likely due to the enhanced persistence of eDNA when associated with clay particles and organic matter. Concentrations of sul1, sul2, tetW, and tetT antibiotic resistance genes were significantly higher in sediment than in water, and were present at higher concentrations as eDNA than as iDNA in sediment. Whereas ARGs (frequently located on plasmid DNA) were detected for over 20 weeks, chromosomally encoded 16S rRNA genes were undetectable after 8 weeks, suggesting higher persistence of plasmid-borne ARGs in river sediment. Transformation of indigenous bacteria with added extracellular ARG (i.e., kanamycin resistance genes) was also observed. Therefore, this study shows that extracellular DNA in sediment is a major ARG reservoir that could facilitate antibiotic resistance propagation.

Ensuring reliable access to clean and affordable water is one of the greatest global challenges of this century. As the world’s population increases, water pollution becomes more complex and difficult to remove, and global climate change threatens to exacerbate water scarcity in many areas, the magnitude of this challenge is rapidly increasing. Wastewater reuse is becoming a common necessity, even as a source of potable water, but our separate wastewater collection and water supply systems are not designed to accommodate this pressing need. Furthermore, the aging centralized water and wastewater infrastructure in the developed world faces growing demands to produce higher quality water using less energy and with lower treatment costs. In addition, it is impractical to establish such massive systems in developing regions that currently lack water and wastewater infrastructure. These challenges underscore the need for technological innovation to transform the way we treat, distribute, use, and reuse water toward a distributed, differential water treatment and reuse paradigm (i.e., treat water and wastewater locally only to the required level dictated by the intended use).Nanotechnology offers opportunities to develop next-generation water supply systems. This Account reviews promising nanotechnology-enabled water treatment processes and provides a broad view on how they could transform our water supply and wastewater treatment systems. The extraordinary properties of nanomaterials, such as high surface area, photosensitivity, catalytic and antimicrobial activity, electrochemical, optical, and magnetic properties, and tunable pore size and surface chemistry, provide useful features for many applications. These applications include sensors for water quality monitoring, specialty adsorbents, solar disinfection/decontamination, and high performance membranes. More importantly, the modular, multifunctional and high-efficiency processes enabled by nanotechnology provide a promising route both to retrofit aging infrastructure and to develop high performance, low maintenance decentralized treatment systems including point-of-use devices.Broad implementation of nanotechnology in water treatment will require overcoming the relatively high costs of nanomaterials by enabling their reuse and mitigating risks to public and environmental health by minimizing potential exposure to nanoparticles and promoting their safer design. The development of nanotechnology must go hand in hand with environmental health and safety research to alleviate unintended consequences and contribute toward sustainable water management.

The increasing likelihood of silver nanoparticle (AgNP) releases to the environment highlights the importance of understanding AgNP interactions with plants, which are cornerstones of most ecosystems. In this study, poplars (Populus deltoides × nigra) and Arabidopsis thaliana were exposed hydroponically to nanoparticles of different sizes (PEG-coated 5 and 10 nm AgNPs, and carbon-coated 25 nm AgNPs) or silver ions (Ag+, added as AgNO3) at a wide range of concentrations (0.01 to 100 mg/L). Whereas all forms of silver were phytotoxic above a specific concentration, a stimulatory effect was observed on root elongation, fresh weight, and evapotranspiration of both plants at a narrow range of sublethal concentrations (e.g., 1 mg/L of 25 nm AgNPs for poplar). Plants were most susceptible to the toxic effects of Ag+ (1 mg/L for poplar, 0.05 mg/L for Arabidopsis), but AgNPs also showed some toxicity at higher concentrations (e.g., 100 mg/L of 25 nm AgNPs for poplar, 1 mg/L of 5 nm AgNPs for Arabidopsis) and this susceptibility increased with decreasing AgNP size. Both poplars and Arabidopsis accumulated silver, but silver distribution in shoot organs varied between plant species. Arabidopsis accumulated silver primarily in leaves (at 10-fold higher concentrations than in the stem or flower tissues), whereas poplars accumulated silver at similar concentrations in leaves and stems. Within the particle subinhibitory concentration range, silver accumulation in poplar tissues increased with exposure concentration and with smaller AgNP size. However, compared to larger AgNPs, the faster silver uptake associated with smaller AgNPs was offset by their toxic effect on evapotranspiration, which was exerted at lower concentrations (e.g., 1 mg/L of 5 nm AgNPs for poplar). Overall, the observed phytostimulatory effects preclude generalizations about the phytotoxicity of AgNPs and encourage further mechanistic research.

Neither amplification nor attenuation of antibiotic resistance genes (ARG) in the environment are well understood processes. Here, we report on continuous culture and batch experiments to determine how tetracycline (TC), aerobic vs anaerobic conditions, bacterial growth rate, and medium richness affect the maintenance of plasmid-borne TC resistance (TetR) genes. The response of E. coli (a model resistant strain excreted by farm animals) versus Pseudomonas aeruginosa (a model bacterium that could serve as a reservoir for ARGs in the environment) were compared to gain insight into response variability. Complete loss of the TetR RP1 plasmid (56 kb) occurred for P. aeruginosa in the absence of TC, and faster loss was observed in continuous culture at higher growth rates. In contrast, E. coli retained its smaller pSC101 plasmid (9.3 kb) after 500 generations without TC (albeit at lower levels, with ratios of resistance to 16S rDNA genes decreasing by about 2-fold). A higher rate of ARG loss was observed in P. aeruginosa when grown in minimal growth medium (M9) than in richer Luria broth. Faster ARG loss occurred in E. coli under anaerobic (fermentative) conditions than under aerobic conditions. Thus, in these two model strains it was observed that conditions that ease the metabolic burden of plasmid reproduction (e.g., higher substrate and O2 availability) enhanced resistance plasmid maintenance; such conditions (in the presence of residual antibiotics) may be conducive to the establishment and preservation of ARG reservoirs in the environment. These results underscore the need to consider antibiotic concentrations, redox conditions, and substrate availability in efforts to evaluate ARG propagation and natural attenuation.

Changes in atmospheric CO2 concentrations, temperature, and precipitation affect plant growth and evapotranspiration. However, the interactive effects of these factors are relatively unexplored, and it is important to consider their combined effects at geographic and temporal scales that are relevant to policymaking. Accordingly, we estimate how climate change would affect water requirements for irrigated corn ethanol production in key regions of the U.S. over a 40 year horizon. We used the geographic-information-system-based environmental policy integrated climate (GEPIC) model, coupled with temperature and precipitation predictions from five different general circulation models and atmospheric CO2 concentrations from the Special Report on Emissions Scenarios A2 emission scenario of the Intergovernmental Panel on Climate Change, to estimate changes in water requirements and yields for corn ethanol. Simulations infer that climate change would increase the evaporative water consumption of the 15 billion gallons per year of corn ethanol needed to comply with the Energy Independency and Security Act by 10%, from 94 to 102 trillion liters/year (tly), and the irrigation water consumption by 19%, from 10.22 to 12.18 tly. Furthermore, on average, irrigation rates would increase by 9%, while corn yields would decrease by 7%, even when the projected increased irrigation requirements were met. In the irrigation-intensive High Plains, this implies increased pressure for the stressed Ogallala Aquifer, which provides water to seven states and irrigates one-fourth of the grain produced in the U.S. In the Corn Belt and Great Lakes region, where more rainfall is projected, higher water requirements could be related to less frequent rainfall, suggesting a need for additional water catchment capacity. The projected increases in water intensity (i.e., the liters of water required during feedstock cultivation to produce 1 L of corn ethanol) because of climate change highlight the need to re-evaluate the corn ethanol elements of the Renewable Fuel Standard.

Soluble di-iron monooxygenases (SDIMOs), especially group-5 SDIMOs (i.e., tetrahydrofuran and propane monooxygenases), are of significant interest due to their potential role in the initiation of 1,4-dioxane (dioxane) degradation. Functional gene array (i.e., GeoChip) analysis of Arctic groundwater exposed to dioxane since 1980s revealed that various dioxane-degrading SDIMO genes were widespread, and PCR-DGGE analysis showed that group-5 SDIMOs were present in every tested sample, including background groundwater with no known dioxane exposure history. A group-5 thmA-like gene was enriched (2.4-fold over background, p < 0.05) in source-zone samples with higher dioxane concentrations, suggesting selective pressure by dioxane. Microcosm assays with 14C-labeled dioxane showed that the highest mineralization capacity (6.4 ± 0.1% 14CO2 recovery during 15 days, representing over 60% of the amount degraded) corresponded to the source area, which was presumably more acclimated and contained a higher abundance of SDIMO genes. Dioxane mineralization ceased after 7 days and was resumed by adding acetate (0.24 mM) as an auxiliary substrate to replenish NADH, a key coenzyme for the functioning of monoxygenases. Acetylene inactivation tests further corroborated the vital role of monooxygenases in dioxane degradation. This is the first report of the prevalence of oxygenase genes that are likely involved in dioxane degradation and suggests their usefulness as biomarkers of dioxane natural attenuation.

Field experiments were conducted to assess the potential for anaerobic biostimulation to enhance BTEX biodegradation under fermentative methanogenic conditions in groundwater impacted by a biodiesel blend (B20, consisting of 20 % v/v biodiesel and 80 % v/v diesel). B20 (100 L) was released at each of two plots through an area of 1 m2 that was excavated down to the water table, 1.6 m below ground surface. One release was biostimulated with ammonium acetate, which was added weekly through injection wells near the source zone over 15 months. The other release was not biostimulated and served as a baseline control simulating natural attenuation. Ammonium acetate addition stimulated the development of strongly anaerobic conditions, as indicated by near-saturation methane concentrations. BTEX removal began within 8 months in the biostimulated source zone, but not in the natural attenuation control, where BTEX concentrations were still increasing (due to source dissolution) 2 years after the release. Phylogenetic analysis using quantitative PCR indicated an increase in concentration and relative abundance of Archaea (Crenarchaeota and Euryarchaeota), Geobacteraceae (Geobacter and Pelobacter spp.) and sulfate-reducing bacteria (Desulfovibrio, Desulfomicrobium, Desulfuromusa, and Desulfuromonas) in the biostimulated plot relative to the control. Apparently, biostimulation fortuitously enhanced the growth of putative anaerobic BTEX degraders and associated commensal microorganisms that consume acetate and H2, and enhance the thermodynamic feasibility of BTEX fermentation. This is the first field study to suggest that anaerobic-methanogenic biostimulation could enhance source zone bioremediation of groundwater aquifers impacted by biodiesel blends.

For nearly a decade, researchers have debated the mechanisms by which AgNPs exert toxicity to bacteria and other organisms. The most elusive question has been whether the AgNPs exert direct “particle-specific” effects beyond the known antimicrobial activity of released silver ions (Ag+). Here, we infer that Ag+ is the definitive molecular toxicant. We rule out direct particle-specific biological effects by showing the lack of toxicity of AgNPs when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag+ release. Furthermore, we demonstrate that the toxicity of various AgNPs (PEG- or PVP- coated, of three different sizes each) accurately follows the dose–response pattern of E. coli exposed to Ag+ (added as AgNO3). Surprisingly, E. coli survival was stimulated by relatively low (sublethal) concentration of all tested AgNPs and AgNO3 (at 3–8 μg/L Ag+, or 12–31% of the minimum lethal concentration (MLC)), suggesting a hormetic response that would be counterproductive to antimicrobial applications. Overall, this work suggests that AgNP morphological properties known to affect antimicrobial activity are indirect effectors that primarily influence Ag+ release. Accordingly, antibacterial activity could be controlled (and environmental impacts could be mitigated) by modulating Ag+ release, possibly through manipulation of oxygen availability, particle size, shape, and/or type of coating.

Little is known about the potential impacts of accidental or incidental releases of manufactured nanomaterials to microbial ecosystem services (e.g., nutrient cycling). Here, quantum dots (QDs) coated with cationic polyethylenimine (PEI) were more toxic to pure cultures of nitrogen-cycling bacteria than QDs coated with anionic polymaleic anhydride-alt-1-octadecene (PMAO). Nitrifying bacteria (i.e., Nitrosomonas europaea) were much more susceptible than nitrogen fixing (i.e., Azotobacter vinelandii, Rhizobium etli, and Azospirillum lipoferum) and denitrifying bacteria (i.e., Pseudomonas stutzeri). Antibacterial activity was mainly exerted by the QDs rather than by their organic coating or their released QD components (e.g., Cd and Zn), which under the near-neutral pH tested (to minimize QD weathering) were released into the bacterial growth media at lower levels than their minimum inhibitory concentrations. Sublethal exposure to QDs stimulated the expression of genes associated with nitrogen cycling. QD-PEI (10 nM) induced three types of nitrogenase genes (nif, anf, and vnf) in A. vinelandii, and one ammonia monooxygenase gene (amoA) in N. europaea was up-regulated upon exposure to 1 nM QD-PEI. We previously reported up-regulation of denitrification genes in P. stutzeri exposed to low concentrations of QD-PEI.(1) Whether this surprising stimulation of nitrogen cycling activities reflects the need to generate more energy to overcome toxicity (in the case of nitrification or denitrification) or to synthesize organic nitrogen to repair or replace damaged proteins (in the case of nitrogen fixation) remains to be determined.

Fuel ethanol releases can stimulate methanogenesis in impacted aquifers, which could pose an explosion risk if methane migrates into enclosed spaces where ignitable conditions exist. To assess this potential risk, a flux chamber was emplaced on a pilot-scale aquifer exposed to continuous release (21 months) of an ethanol solution (10% v:v) that was introduced 22.5 cm below the water table. Despite methane concentrations within the ethanol plume reaching saturated levels (20–23 mg/L), the maximum methane concentration reaching the chamber (21 ppmv) was far below the lower explosion limit in air (50,000 ppmv). The low concentrations of methane observed in the chamber are attributed to methanotrophic activity, which was highest in the capillary fringe. This was indicated by methane degradation assays in microcosms prepared with soil samples from different depths, as well as by PCR measurements of pmoA, which is a widely used functional gene biomarker for methanotrophs. Simulations with the analytical vapor intrusion model “Biovapor” corroborated the low explosion risk associated with ethanol fuel releases under more generic conditions. Model simulations also indicated that depending on site-specific conditions, methane oxidation in the unsaturated zone could deplete the available oxygen and hinder aerobic benzene biodegradation, thus increasing benzene vapor intrusion potential. Overall, this study shows the importance of methanotrophic activity near the water table to attenuate methane generated from dissolved ethanol plumes and reduce its potential to migrate and accumulate at the surface.

The growing use of quantum dots (QDs) in numerous applications increases the possibility of their release to the environment. Bacteria provide critical ecosystem services, and understanding their response to QDs is important to assess the potential environmental impacts of such releases. Here, we analyze the microbial response to sublethal exposure to commercial QDs, and investigate potential defense and adaptation mechanisms in the model bacterium Pseudomonas aeruginosa PAO1. Both intact and weathered QDs, as well as dissolved metal constituents, up-regulated czcABC metal efflux transporters. Weathered QDs also induced superoxide dismutase gene sodM, which likely served as a defense against oxidative stress. Interestingly, QDs also induced antibiotic resistance (ABR) genes and increased antibiotic minimum inhibitory concentrations by 50 to 100%, which suggests up-regulation of global stress defense mechanisms. Extracellular synthesis of nanoparticles (NPs) was observed after exposure to dissolved Cd(NO3)2 and SeO2. With extended X-ray absorption fine structure (EXAFS), we discerned biogenic NPs such as CdO, CdS, CdSe, and selenium sulfides. These results show that bacteria can mitigate QD toxicity by turning on energy-dependent heavy-metal ion efflux systems and by mediating the precipitation of dissolved metal ions as less toxic and less bioavailable insoluble NPs.Keywords: extended X-ray absorption fine structure; extracellular nanoparticle biosynthesis; gene expression; nanoparticles; Pseudomonas aeruginosa; quantum dots

The occurrence and transport of 12 antibiotics (from the tetracycline, sulfonamide, quinolone, and macrolide families) was studied in a 72-km stretch of the Haihe River, China, and in six of its tributaries. Aqueous and sediment samples were analyzed by HPLC−MS/MS. Sulfonamides were detected at the highest concentrations (24−385 ng/L) and highest frequencies (76−100%). Eight of the 12 antibiotics likely originated from veterinary applications in swine farms and fishponds, and concentrations at these sources (0.12−47 μg/L) were 1−2 orders of magnitude higher than in the effluent of local wastewater treatment plants. Sulfachloropyridazine (SCP) was detected in all swine farm and fishpond samples (maximum concentration 47 μg/L), which suggests its potential usefulness to indicate livestock source pollution in the Haihe River basin. Hydrological and chemical factors that may influence antibiotic distribution in the Haihe River were considered by multiple regression analysis. River flow rate exerted the most significant effect on the first-order attenuation coefficient (K) for sulfonamides, quinolones, and macrolides, with higher flow rates resulting in higher K, probably due to dilution. For tetracyclines, sediment total organic matter and cation exchange capacity exerted a greater impact on K than flow rate, indicating that adsorption to sediments plays an important role in attenuating tetracycline migration. Overall, the predominance of sulfonamides in the Haihe River underscores the need to consider regulating their veterinary use and improving the management and treatment of associated releases.

In this 10 year study, Brazilian gasoline (100 L, containing 24% ethanol by volume) was released to a sandy aquifer to evaluate the natural attenuation of benzene, toluene, ethylbenzene, and total xylenes (BTEX) in the presence of ethanol. Groundwater concentrations of BTEX, ethanol, and degradation products (e.g., acetate and methane) were measured over the entire plume using an array of monitoring well clusters, to quantify changes in plume mass and region of influence. Ethanol biodegradation coincided with the development of methanogenic conditions while acetate (a common anaerobic metabolite) accumulated. The benzene plume expanded beyond the 30 m long monitored area and began to recede after 2.7 years, when ethanol had disappeared. Theoretical calculations suggest that the transient accumulation of acetate (up to 166 mg L−1) may have hindered the thermodynamic feasibility of benzene degradation under methanogenic conditions. Yet, benzene removal proceeded relatively fast compared to literature values (and faster than the alkylbenzenes present at this site) after acetate concentrations had decreased below inhibitory levels. Thus, site investigations of ethanol blend releases should consider monitoring acetate concentrations. Overall, this study shows that inhibitory effects of ethanol and acetate are relatively short-lived, and demonstrates that monitored natural attenuation can be a viable option to deal with ethanol blend releases.

Pseudomonas stutzeri was exposed to quantum dots (QDs) with three different surface coatings (anionic polymaleic anhydride-alt-1-octadecene (PMAO), cationic polyethylenimine (PEI), and carboxyl QDs) under both aerobic and anaerobic (denitrifying) conditions. Under aerobic conditions, toxicity (assessed per growth inhibition) increased from PMAO to carboxyl to PEI QDs. The positive charge of PEI facilitated direct contact with negatively charged bacteria, which was verified by TEM analysis. Both PMAO and PEI QDs hindered energy transduction (indicated by a decrease in cell membrane potential), and this effect was most pronounced with PEI QDs under denitrifying conditions. Up-regulation of denitrification genes (i.e., nitrate reductase narG, periplasmic nitrate reductase napB, nitrite reductase nirH, and NO reductase norB) occurred upon exposure to subinhibitory PEI QD concentrations (1 nM). Accordingly, denitrification activity (assessed per respiratory nitrate consumption in the presence of ammonia) increased during sublethal PEI QD exposure. However, cell viability (including denitrification) was hindered at 10 nM or higher PEI QD concentrations. Efflux pump genes czcB and czcC were induced by PEI QDs under denitrifying conditions, even though Cd and Se dissolution from QDs did not reach toxic levels (exposure was at pH 7 to minimize hydrolysis of QD coatings and the associated release of metal constituents). Up-regulation of the superoxide dismutase (stress) gene sodB occurred only under aerobic conditions, likely due to intracellular production of reactive oxygen species (ROS). The absence of ROS under denitrifying conditions suggests that the antibacterial activity of QDs was not due to ROS production alone. Overall, this work forewarns about unintended potential impacts to denitrification as a result of disposal and incidental releases of QDs, especially those with positively charged coatings (e.g., PEI QDs).

The antibacterial activity of silver nanoparticles (AgNPs) is partially due to the release of Ag+, although discerning the contribution of AgNPs vs Ag+ is challenging due to their common co-occurrence. We discerned the toxicity of Ag+ versus a commercially available AgNP (35.4 ± 5.1 nm, coated with amorphous carbon) by conducting antibacterial assays under anaerobic conditions that preclude Ag(0) oxidation, which is a prerequisite for Ag+ release. These AgNPs were 20× less toxic to E. coli than Ag+ (EC50: 2.04 ± 0.07 vs 0.10 ± 0.01 mg/L), and their toxicity increased 2.3-fold after exposure to air for 0.5 h (EC50: 0.87 ± 0.03 mg/L) which promoted Ag+ release. No significant difference in Ag+ toxicity was observed between anaerobic and aerobic conditions, which rules out oxidative stress by ROS as an important antibacterial mechanism for Ag+. The toxicity of Ag+ (2.94 μmol/L) was eliminated by equivalent cysteine or sulfide; the latter exceeded the solubility product equilibrium constant (Ksp), which is conducive to silver precipitation. Equivalent chloride and phosphate concentrations also reduced Ag+ toxicity without exceeding Ksp. Thus, some common ligands can hinder the bioavailability and mitigate the toxicity of Ag+ at relatively low concentrations that do not induce silver precipitation. Furthermore, low concentrations of chloride (0.1 mg/L) mitigated the toxicity of Ag+ but not that of AgNPs, suggesting that previous reports of higher AgNPs toxicity than their equivalent Ag+ concentration might be due to the presence of common ligands that preferentially decrease the bioavailability and toxicity of Ag+. Overall, these results show that the presence of O2 or common ligands can differentially affect the toxicity of AgNPs vs Ag+, and underscore the importance of water chemistry in the mode of action of AgNPs.

We recently reported that C60 aminofullerenes immobilized on silica support (aminoC60/silica) efficiently produce singlet oxygen (1O2) and inactivate virus and bacteria under visible light irradiation.(1) We herein evaluate this new photocatalyst for oxidative degradation of 11 emerging organic contaminants, including pharmaceuticals such as acetaminophen, carbamazepine, cimetidine, propranolol, ranitidine, sulfisoxazole, and trimethoprim, and endocrine disruptors such as bisphenol A and pentachlorophenol. Tetrakis aminoC60/silica degraded pharmaceuticals under visible light irradiation faster than common semiconductor photocatalysts such as platinized WO3 and carbon-doped TiO2. Furthermore, aminoC60/silica exhibited high target-specificity without significant interference by natural organic matter. AminoC60/silica was more efficient than unsupported (water-suspended) C60 aminofullerene. This was attributed to kinetically enhanced 1O2 production after immobilization, which reduces agglomeration of the photocatalyst, and to adsorption of pharmaceuticals onto the silica support, which increases exposure to 1O2 near photocatalytic sites. Removal efficiency increased with pH for contaminants with a phenolic moiety, such as bisphenol A and acetaminophen, because the electron-rich phenolates that form at alkaline pH are more vulnerable to singlet oxygenation.

Nanoscale zerovalent iron (NZVI) can be used to dechlorinate trichloroethylene (TCE) in contaminated aquifers. Dehalococcoides spp. is the only microbial genus known to dechlorinate TCE to ethene as a respiratory process. However, little is known about how NZVI affects the expression of genes coding for reductive dechlorination. We examined a high-rate TCE-dechlorinating mixed culture which contains organisms similar to known Dehalococcoides to study the effects of NZVI on the expression of two model genes coding for reductive dehalogenases (tceA and vcrA). A novel pretreatment approach, relying on magnetic separation of NZVI prior to reverse transcription qPCR (to avoid RNA adsorption by NZVI), was developed and used with relative quantification (relative to 16S rRNA as endogenous housekeeping gene) to quantify reductive dehalogenase gene expression. Both tceA and vcrA were significantly down-regulated (97- and 137-fold, respectively) relative to baseline (time 0) conditions after 72-h exposure to chlorinated ethenes (0.12 ± 0.03 mg/L cis-DCE, 0.69 ± 0.11 mg/L t-DCE, and 0.54 ± 0.16 mg/L VC) and bare-NZVI (1 g-NZVI/L). However, coating NZVI with an olefin maleic acid copolymer (a common approach to enhance its mobility in aquifers) overcame this significant inhibitory effect, and both tceA and vcrA were up-regulated (3.0- and 3.5-fold, respectively) after 48-h exposure. Thus, NZVI coating might enhance the expression of dechlorinating genes and the concurrent or sequential participation of Dehalococcoides spp. in the remediation process.

The occurrence of antibiotics and antibiotic resistance genes (ARGs) was quantified in water and sediment samples collected from a 72 km stretch of the Haihe River, China. Tetracycline resistance genes (tetW, tetQ, tetO, tetT, tetM, tetB, and tetS) were not detected by quantitative PCR in many samples. In contrast, sul1 and sul2 (coding for sulfonamide resistance) were present at relatively high concentrations in all (38) samples. The highest ARG concentrations detected were (7.8 ± 1.0) × 109 copies/g for sul1 and (1.7 ± 0.2) × 1011 copies/g for sul2, in sediment samples collected during the summer. The corresponding total bacterial concentration (quantified with a universal 16S-rDNA probe) was (3.3 ± 0.4) × 1012 cells/g. Sul1 and sul2 concentrations in sediments were 120−2000 times higher than that in water, indicating that sediments are an important ARG reservoir in the Haihe River. Statistical analysis indicated a positive correlation between the relative abundance of these ARGs (i.e., sul1/16S-rDNA and sul2/16S-rDNA) and the total concentration of sulfamethoxazole, sulfadiazine, plus sulfachlororyridazine, suggesting that sulfonamides exerted selective pressure for these ARGs. A class 1 integron was implicated in the propagation of sul1. Overall, the widespread distribution of sulfonamide ARGs underscores the need to better understand and mitigate their propagation in the environment and the associated risks to public health.

Carbon fullerenes, including buckminsterfullerene (C60), are increasingly available for numerous applications, thus increasing the likelihood of environmental release. This calls for information about their bioavailability and bioaccumulation potential. In this study, 14C-labeled C60 and 14C-phenanthrene (positive control) were added separately to soils of varying composition and organic carbon content (OC), and their bioaccumulation in the earthworm Eisenia fetida was compared. Biota-sediment accumulation factors (BSAF) were measured after 24 h depuration in soils with high C60 dosages (60, 100, and 300 mg-C60 kg−1 dry soil), which exceed the soil sorption capacity, as well as in soils with a low C60 dose (0.25 mg kg−1) conducive to a high fraction of sorbed molecular C60. The BSAF value for the low-dose soil (0.427) was 1 order of magnitude lower than for less hydrophobic phenanthrene (7.93), inconsistent with the equilibrium partition theory that suggests that BSAF should be constant and independent of the KOW value of the chemical. Apparently, the large molecular size of C60 hinders uptake and bioaccumulation. Lower BSAF values (0.065−0.13) were measured for high-dose soils, indicating that C60 bioaccumulates more readily when a higher fraction of molecular C60 (rather than larger precipitates) is available. For the high-dose tests (heterogeneous C60 system), soil OC content did not significantly affect the extent of C60 bioaccumulation after 28 d of incubation, although higher OC content resulted in faster initial bioaccumulation. For low-dose soils, C60 BSAF decreased with increasing soil OC, as commonly reported for hydrophobic chemicals due to partitioning into soil OC. There was no detectable transformation of 14C60 in either soil or worm tissue. Overall, the relatively low extent but rapid bioaccumulation of C60 in E. fetida suggests the need for further studies on the potential for trophic transfer and biomagnification.

A new strategy is described to immobilize photoactive C60 aminofullerene on silica gel (3-(2-succinic anhydride)propyl functionalized silica), thus enabling facile separation of the photocatalyst for recycling and repeated use. An organic linker moiety containing an amide group was used to anchor C60 aminofullerene to the functionalized silica support. The linker moiety prevents aqueous C60 aggregation/agglomeration (shown by TEM images), resulting in a remarkable enhancement of photochemical 1O2 production under visible light irradiation. With no loss in efficacy of 1O2 production plus insignificant chemical modification of the aminoC60/silica photocatalyst after multiple cycling, the system offers a promising new visible-light-activated photocatalyst. Under visible-light irradiation, the aminoC60/silica photocatalyst is capable of effective and kinetically enhanced oxidation of Ranitidine and Cimetidine (pharmaceutical pollutants) and inactivation of MS-2 bacteriophage compared to aqueous solutions of the C60 aminofullerene alone. Thus, this photocatalyst could enable water treatment in less developed areas by alleviating dependence on major infrastructure, including the need for electricity.

The extraordinary chemical and physical properties of materials at the nanometer scale enable novel applications ranging from structural strength enhancement and energy conservation to antimicrobial properties and self-cleaning surfaces. Consequently, manufactured nanomaterials (MNMs) and nanocomposites are being considered for various uses in the construction and related infrastructure industries. To achieve environmentally responsible nanotechnology in construction, it is important to consider the lifecycle impacts of MNMs on the health of construction workers and dwellers, as well as unintended environmental effects at all stages of manufacturing, construction, use, demolition, and disposal. Here, we review state-of-the-art applications of MNMs that improve conventional construction materials, suggest likely environmental release scenarios, and summarize potential adverse biological and toxicological effects and their mitigation. Aligned with multidisciplinary assessment of the environmental implications of emerging technologies, this review seeks to promote awareness of potential benefits of MNMs in construction and stimulate the development of guidelines to regulate their use and disposal to mitigate potential adverse effects on human and environmental health.Keywords: bioavailability; concrete; exposure; industrial ecology; labeling; oxidative stress; risk assessment; sensor; toxicity; windows

The assessment of biodegradation activity in contaminated aquifers is critical to demonstrate the performance of bioremediation and natural attenuation and to parameterize models of contaminant plume dynamics. Real time quantitative PCR (qPCR) was used to target the catabolic bssA gene (coding for benzylsuccinate synthase) and a 16S rDNA phylogenetic gene (for total Bacteria) as potential biomarkers to infer on anaerobic toluene degradation rates. A significant correlation (P = 0.0003) was found over a wide range of initial toluene concentrations (1–100 mg/l) between toluene degradation rates and bssA concentrations in anaerobic microcosms prepared with aquifer material from a hydrocarbon contaminated site. In contrast, the correlation between toluene degradation activity and total Bacteria concentrations was not significant (P = 0.1125). This suggests that qPCR targeting of functional genes might offer a simple approach to estimate in situ biodegradation activity, which would enhance site investigation and modeling of natural attenuation at hydrocarbon-contaminated sites.

Four novel hexakis C60 derivatives with varying functionalities were synthesized, and their photochemical properties and photodynamic disinfection efficiencies were quantitatively evaluated. All these C60 derivatives generated 1O2 more efficiently than commercial multihydroxylated C60 (fullerol), as assessed by furfuryl alcohol consumption and electron paramagnetic resonance analysis. Despite significant agglomeration/aggregation in the aqueous phase to micrometer-sized particles, nanosecond laser flash photolysis showed that the lifetime of triplet state (a key intermediate for energy transfer responsible for 1O2 production) was comparable to reported values for pristine C60 in organic phase. As a result of facile 1O2 production, the C60 derivatives efficiently inactivated Escherichia coli and MS-2 bacteriophage. Cationic aminofullerene hexakis, which likely exerted electrostatic attraction, exhibited exceptionally rapid virus inactivation even compared to commercial nano-TiO2 photocatalyst. These unique photodynamic, hydrophilic and cationic properties may be instrumental for the development of next generation photocatalysts for disinfection applications. The high ROS (reactive oxygen species) production activity and associated cytotoxicity are concerns for potential releases of functionalized C60 to the environment, and require careful assessment apart from other forms of C60 (e.g., nC60) that have been widely studied as model nanomaterials but behave differently.

Manufactured nanomaterials (MNMs) are rapidly being incorporated into a wide variety of commercial products with significant potential for environmental release, which calls for eco-responsible design and disposal of nanoenabled products. Critical research needs to advance this urgent priority include (1) structure−activity relationships to predict functional stability and chemistry of MNMs in the environment and to discern properties that increase their bioavailability, bioaccumulation, and toxicity; (2) standardized protocols to assess MNM bioavailability, trophic transfer, and sublethal effects; and (3) validated multiphase fate and transport models that consider various release scenarios and predict the form and concentration of MNMs at the point of exposure. These efforts would greatly benefit from the development of robust analytical techniques to characterize and to track MNMs in the environment and to validate models and from shared reference MNM libraries.

The cytotoxic and antibacterial properties of nC60, a buckminsterfullerene water suspension, have been attributed to photocatalytically generated reactive oxygen species (ROS). However, in this work, neither ROS production nor ROS-mediated damage is found in nC60-exposed bacteria. Furthermore, the colorimetric methods used to evaluate ROS production and damage are confounded by interactions between nC60 and the reagents, yielding false positives. Instead, we propose that nC60 exerts ROS-independent oxidative stress, thus reconciling conflicting results in the literature.

Quantum dots (QDs) are increasingly being used for electronics, solar energy generation, and medical imaging applications. Most QDs consist of a heavy metal core/shell coated with amphiphilic organics that stabilize the nanoparticles and allow conjugation with biological molecules. In this study, QDs were evaluated for their effects on bacterial pure cultures, which serve as models of cell toxicity and indicators of potential impact to ecosystem health. QDs with intact surface coatings decreased growth rates of Gram positive Bacillus subtilis and Gram negative Escherichia coli but were not bactericidal. In contrast, weathering of various types of QDs under acidic (pH ≤ 4) or alkaline (pH ≥ 10) conditions significantly increased bactericidal activity due to the rapid (<1 min) release of cadmium and selenite ions following QD destabilization upon loss of the organic coating. Toxicity was mitigated by humic acids, proteins, and other organic ligands that reduced metal bioavailability. The best available science, which is limited, suggests that QDs are potentially safe materials when used in their intended applications at near-neutral pH. These results forewarn us that even moderately acidic or alkaline conditions could lead to significant and localized organism effects due to toxic exposure to dissolved heavy metals. Thus, biocompatibility and ecotoxicity tests for QDs should consider in vivo and/or in situ transformations to fully characterize the potential risks to environmental health.

Buckminsterfullerene (C60) can form water suspensions (nC60) that exert toxic effects. While reactive oxygen species (ROS) generation has been implicated as the mechanism for mammalian cytotoxicity, we propose that nC60 exerts ROS-independent oxidative stress in bacteria, with evidence of protein oxidation, changes in cell membrane potential, and interruption of cellular respiration. This mechanism requires direct contact between the nanoparticle and the bacterial cell and differs from previously reported nanomaterial antibacterial mechanisms that involve ROS generation (metal oxides) or leaching of toxic elements (nanosilver).

Flow-through aquifer columns were operated for 12 weeks to evaluate the benefits of aerobic biostimulation for the bioremediation of source-zone soil contaminated with chlorobenzenes (CBs). Quantitative Polymerase Chain Reaction (qPCR) was used to measure the concentration of total bacteria (16S rRNA gene) and oxygenase genes involved in the biodegradation of aromatic compounds (i.e., toluene dioxygenase, ring hydroxylating monooxygenase, naphthalene dioxygenase, phenol hydroxylase, and biphenyl dioxygenase). Monochlorobenzene, which is much more soluble than dichlorobenzenes, was primarily removed by flushing, and biostimulation showed little benefit. In contrast, dichlorobenzene removal was primarily due to biodegradation, and the removal efficiency was much higher in oxygen-amended columns compared to a control column. To our knowledge, this is the first report that oxygen addition can enhance CB source-zone soil bioremediation. Analysis by qPCR showed that whereas the biphenyl and toluene dioxygenase biomarkers were most abundant, increases in the concentration of the phenol hydroxylase gene reflected best the higher dichlorobenzene removal due to aerobic biostimulation. This suggests that quantitative molecular microbial ecology techniques could be useful to assess CB source-zone bioremediation performance.

7-Ketocholesterol (7KC) is an oxidized derivative of cholesterol suspected to be involved in the pathogenesis of atherosclerosis and possibly Alzheimer’s disease. While some oxysterols are important biological mediators, 7KC is generally cytotoxic and interferes with cellular homeostasis. Despite recent interest in preventing the accumulation of 7KC in a variety of matrices to avoid adverse biological effects, its microbial degradation has not been previously addressed in the peer-reviewed literature. Thus, the rate and extent of biodegradation of this oxysterol was investigated to bridge this gap. A wide variety of bacteria isolated from soil or activated sludge, including Proteobacterium Y-134, Sphingomonas sp. JEM-1, Nocardia nova, Rhodococcus sp. RHA1, and Pseduomonas aeruginosa, utilized 7KC as a sole carbon and energy source, resulting in its mineralization. Nocardia nova, which is known to produce biosurfactants, was the fastest degrader. This study supports the notion that microbial catabolic enzymes could be exploited to control 7KC levels in potential biotechnological applications for agricultural, environmental, or medical use.

The availability of clean water is necessary for all aspects of food production, preparation, distribution and consumption. Yet the magnitude, intensity and diversity of water pollution and the depletion of some water resources continue to grow, reducing the availability of clean, usable water and raising the potential for a water-related crisis that would have a severe impact on food processes. These impacts could be especially severe in developing nations where water supplies and treatment technologies are limited. Nanotechnology shows great promise as a feasible means of treating both long-standing and emerging water contaminants, as well as enabling technologies such as desalination of seawater to increase water supply. However, some engineered nanomaterials could also become water pollutants that threaten public and ecosystem health. Accordingly, this paper considers both the applications and implications of nanotechnology within the context of water quality and water security for developing countries.

Flow-through column studies were conducted to mimic the natural attenuation of ethanol and BTEX mixtures, and to consider potential inhibitory effects of ethanol and its anaerobic metabolite acetate on BTEX biodegradation. Results were analyzed using a one-dimensional analytical model that was developed using consecutive reaction differential equations based on first-order kinetics. Decrease in pH due to acetogenesis was also modeled, using charge balance equations under CaCO3 dissolution conditions. Delay in BTEX removal was observed and simulated in the presence of ethanol and acetate. Acetate was the major volatile fatty acid intermediate produced during anaerobic ethanol biodegradation (accounting for about 58% of the volatile fatty acid mass) as suggested by the model data fit. Acetate accumulation (up to 1.1 g/L) near the source zone contributed to a pH decrease by almost one unit. The anaerobic degradation of ethanol (2 g/L influent concentration) at the source zone produced methane at concentrations exceeding its solubility (≅ 26 mg/L). Overall, this simple analytical model adequately described ethanol degradation, acetate accumulation and methane production patterns, suggesting that it could be used as a screening tool to simulate lag times in BTEX biodegradation, changes in groundwater pH and methane generation following ethanol-blended fuel releases.Highlights► A model was developed as screening tool to assess BTEX attenuation in gasohol plume. ► Simulation of ethanol degradation and acetate production served to predict BTEX degradation lag time. ► Changes in groundwater pH due to fatty acids accumulation was assessed by the model. ► Methane concentrations was predicted by the analytical model.

Fuel releases that impact groundwater are a common occurrence, and the growing use of ethanol as a transportation biofuel is increasing the likelihood of encountering ethanol in such releases. Microorganisms play a critical role in the fate of ethanol-blended fuel releases, often determining their region of influence and potential impacts. This review summarizes current understanding on the biogeochemical footprint of such releases and the factors that influence their natural attenuation. Implications for site investigation, risk assessment and remediation strategies are also addressed along with research priorities.Graphical abstractDownload high-res image (81KB)Download full-size imageHighlights► Ethanol could hinder BTEX attenuation by various biogeochemical mechanisms. ► O2 depletion, enzyme repression and metabolic flux dilution elongate BTEX plumes. ► Elongation is site-specific and is offset by fortuitous growth of BTEX degraders. ► Ethanol migrates through the capillary fringe, a zone of high microbial activity. ► Ethanol-derived CH4 could pose an explosion risk and enhance BTEX vapor intrusion.

Thermal treatment technologies hold an important niche in the remediation of hydrocarbon-contaminated soils and sediments due to their ability to quickly and reliably meet cleanup standards. However, sustained high temperature can be energy intensive and can damage soil properties. Despite the broad applicability and prevalence of thermal remediation, little work has been done to improve the environmental compatibility and sustainability of these technologies. We review several common thermal treatment technologies for hydrocarbon-contaminated soils, assess their potential environmental impacts, and propose frameworks for sustainable and low-impact deployment based on a holistic consideration of energy and water requirements, ecosystem ecology, and soil science. There is no universally appropriate thermal treatment technology. Rather, the appropriate choice depends on the contamination scenario (including the type of hydrocarbons present) and on site-specific considerations such as soil properties, water availability, and the heat sensitivity of contaminated soils. Overall, the convergence of treatment process engineering with soil science, ecosystem ecology, and plant biology research is essential to fill critical knowledge gaps and improve both the removal efficiency and sustainability of thermal technologies.

Antibacterial fullerene-based particles, termed nC60, were coated onto a polystyrene surface to evaluate their ability to prevent biofilm formation by Pseudomonas mendocina. Biofilm growth on this surface was assessed using ethidium bromide staining and SEM, and cell viability was determined using live/dead fluorescent cell staining. Unexpectedly, surfaces coated with nC60 developed a biofilm earlier than the uncoated control, and a higher percentage of live bacteria. This shows that some antimicrobial nanomaterials may lose their efficacy when applied as coatings. The nC60 coating appeared to encourage rather than discourage biofilm formation. Furthermore, the bacteria that adhered to the surface were not killed, implying that while nC60 would not perform well in this application, the electronic properties of fullerenes and their apparent ability to encourage biofilm formation should be investigated for potential microbial fuel cell applications.

Biochar has a great potential for enhancing soil fertility and carbon sequestration while enabling beneficial waste disposition. Because of the potential for widespread application, it is essential to proactively assess and mitigate any unintended consequences associated with soil biochar amendment. We conducted soil avoidance tests, growth and reproduction tests, and oxidative stress assays with the earthworm Eisenia foetida to assess the potential toxicity of soil amended with biochar produced from apple wood chips. Earthworms avoided soils containing 100 and 200 g/kg dry biochar at statistically significant levels (p < 0.05), and after 28-day incubation, these earthworms lost more weight than those in control (unamended) soil. However, biochar did not affect the reproduction of earthworms. We investigated whether the observed avoidance was due to nutrition deficiency, desiccation, or the presence of toxic polynuclear aromatic hydrocarbons (PAHs) formed during biochar production by pyrolysis. Nutrition deficiency was excluded by the lack of earthworm avoidance to soil amended with nutrient-deficient sand instead of biochar. Although traces of PAH were detected in the tested biochar (e.g., 25.9 μg/kg fluorene, 3290 μg/kg naphthalene, and 102 μg/kg phenanthrene), the lack of lipid peroxidation and no increase in superoxide dismutase activity in biochar-exposed earthworms suggests that presence of toxic compounds was not a likely reason for avoidance. Furthermore, wetting the biochar to its field capacity resulted in statistically undetectable avoidance relative to control soil, indicating that insufficient moisture could be a key factor affecting earthworm behavior in soil amended with dry biochar. To avoid desiccation of invertebrates and enable their beneficial ecosystem services, we recommend wetting biochar either before or immediately after soil application.Highlights► Earthworms avoided soils with high concentrations (≥100 mg/kg) of dry biochar. ► Avoidance averted desiccation rather than biochar-related PAHs or nutrient scarcity. ► Earthworms in biochar-amended soil experienced significant weight loss. ► Wetting the biochar before exposure mitigated avoidance by earthworms.

The effects of five fuel alcohols (methanol, ethanol, 1-propanol, iso-butanol and n-butanol) on the natural attenuation of benzene were compared using a previously developed numerical model (General Substrate Interaction Module — GSIM) and a probabilistic sensitivity analysis. Simulations with a 30 gal dissolving LNAPL (light non-aqueous phase liquid) source consisting of a range of gasoline blends (10% and 85% v:v alcohol content) suggest that all fuel alcohols can hinder the natural attenuation of benzene, due mainly to accelerated depletion of dissolved oxygen and a decrease in the specific degradation rate for benzene (due to catabolite repression and metabolic flux dilution). Simulations for blends with 10% alcohol, assuming a homogeneous sandy aquifer, inferred maximum benzene plume elongations (relative to a regular gasoline release) of 26% for ethanol, 47% for iso-butanol, 147% for methanol, 188% for 1-propanol, and 265% for n-butanol. The corresponding elongation percentages for blends with 85% alcohol were generally smaller (i.e., 25%, 54%, 135%, 163%, and 181%, respectively), reflecting a lower content of benzene in the simulated release. Benzene plume elongation and longevity were more pronounced in the presence of alcohols that biodegrade slower (e.g., propanol and n-butanol), forming longer and more persistent alcohol plumes. Conversely, ethanol and iso-butanol exhibited the lowest potential to hinder the natural attenuation of benzene, illustrating the significant effect that a small difference in chemical structure (e.g., isomers) can have on biodegradation. Overall, simulations were highly sensitive to site-specific biokinetic coefficients for alcohol degradation, which forewarns against generalizations about the level of impact of specific fuel alcohols on benzene plume dynamics.