Showing papers in "Environmental Science & Technology in 2008"
TL;DR: The results of this study make it possible for the first time to carry out a quantitative risk assessment of nanoparticles in the environment and suggest further detailed studies of nano-TiO2.
Abstract: The aim of this study was to use a life-cycle perspective to model the quantities of engineered nanoparticles released into the environment. Three types of nanoparticles were studied: nano silver (nano-Ag), nano TiO2 (nano-TiO2), and carbon nanotubes (CNT). The quantification was based on a substance flow analysis from products to air, soil, and water in Switzerland. The following parameters were used as model inputs: estimated worldwide production volume, allocation of the production volume to product categories, particle release from products, and flow coefficients within the environmental compartments. The predicted environmental concentrations (PEC) were then compared to the predicted no effect concentrations (PNEC) derived from the literature to estimate a possible risk. The expected concentrations of the three nanoparticles in the different environmental compartments vary widely, caused by the different life cycles of the nanoparticle-containing products. The PEC values for nano-TiO2 in water are 0....
1,776 citations
TL;DR: The data indicate as plastic fragments into smaller particles, the potential for accumulation in the tissues of an organism increases and further work using a wider range of organisms, polymers, and periods of exposure will be required to establish the biological consequences of this debris.
Abstract: Plastics debris is accumulating in the environment and is fragmenting into smaller pieces; as it does, the potential for ingestion by animals increases. The consequences of macroplastic debris for wildlife are well documented, however the impacts of microplastic (< 1 mm) are poorly understood. The mussel, Mytilus edulis, was used to investigate ingestion, translocation, and accumulation of this debris. Initial experiments showed that upon ingestion, microplastic accumulated in the gut. Mussels were subsequently exposed to treatments containing seawater and microplastic (3.0 or 9.6 microm). After transfer to clean conditions, microplastic was tracked in the hemolymph. Particles translocated from the gut to the circulatory system within 3 days and persisted for over 48 days. Abundance of microplastic was greatest after 12 days and declined thereafter. Smaller particles were more abundant than larger particles and our data indicate as plastic fragments into smaller particles, the potential for accumulation in the tissues of an organism increases. The short-term pulse exposure used here did not result in significant biological effects. However, plastics are exceedingly durable and so further work using a wider range of organisms, polymers, and periods of exposure will be required to establish the biological consequences of this debris.
1,708 citations
TL;DR: Variable leaching rates among sock types suggests that the sock manufacturing process may control the release of silver, and physical separation and ion selective electrode (ISE) analyses suggest that both colloidal and ionic silver leach from the socks.
Abstract: Manufacturers of clothing articles employ nanosilver (n-Ag) as an antimicrobial agent, but the environmental impacts of n-Ag release from commercial products are unknown. The quantity and form of the nanomaterials released from consumer products should be determined to assess the environmental risks of nanotechnology. This paper investigates silver released from commercial clothing (socks) into water, and its fate in wastewater treatment plants (WWTPs). Six types of socks contained up to a maximum of 1360 µg-Ag/g-sock and leached as much as 650 µg of silver in 500 mL of distilled water. Microscopy conducted on sock material and wash water revealed the presence of silver particles from 10 to 500 nm in diameter. Physical separation and ion selective electrode (ISE) analyses suggest that both colloidal and ionic silver leach from the socks. Variable leaching rates among sock types suggests that the sock manufacturing process may control the release of silver. The adsorption of the leached silver to WWTP biom...
1,703 citations
TL;DR: The results indicate that the interaction of these particles with algae influences the toxicity of AgNP, which is mediated by Ag+.
Abstract: Silver nanoparticles (AgNP) are likely to enter the aquatic environment because of their multiple uses. We have examined the short-term toxicity of AgNP and ionic silver (Ag+) to photosynthesis in Chlamydomonas reinhardtii using fluorometry. AgNP ranged in size from 10 to 200 nm with most particles around 25 nm. As determined by DGT (diffusive gradients in thin films), by ion-selective electrode, and by centrifugal ultrafiltration, about 1% of the AgNP was present as Ag+ ions. Based on total Ag concentration, toxicity was 18 times higher for AgNO3 than for AgNP (in terms of EC50). However, when compared as a function of the Ag+ concentration, toxicity of AgNP appeared to be much higher than that of AgNO3. The ionic Ag+ measured in the AgNP suspensions could not fully explain the observed toxicity. Cysteine, a strong Ag+ ligand, abolished the inhibitory effects on photosynthesis of both AgNP and Ag+. Together, the results indicate that the interaction of these particles with algae influences the toxicity o...
1,453 citations
TL;DR: Biochars, produced by pyrolysis of pine needles at different temperatures, were characterized by elemental analysis, BET-N2 surface areas and FTIR, and Sorption isotherms of naphthalene, nitrobenzene, and m-dinitrobenZene from water to the biochars were compared.
Abstract: The combined adsorption and partition effects of biochars with varying fractions of noncarbonized organic matter have not been clearly defined. Biochars, produced by pyrolysis of pine needles at different temperatures (100-700 degrees C, referred as P100-P700), were characterized by elemental analysis, BET-N2 surface areas and FTIR. Sorption isotherms of naphthalene, nitrobenzene, and m-dinitrobenzene from water to the biochars were compared. Sorption parameters (N and logKf) are linearly related to sorbent aromaticities, which increase with the pyrolytic temperature. Sorption mechanisms of biochars are evolved from partitioning-dominant at low pyrolytic temperatures to adsorption-dominant at higher pyrolytic temperatures. The quantitative contributions of adsorption and partition are determined by the relative carbonized and noncarbonized fractions and their surface and bulk properties. The partition of P100-P300 biochars originates from an amorphous aliphatic fraction, which is enhanced with a reduction of the substrate polarity; for P400-P600, the partition occurs with a condensed aromatic core that diminishes with a further reduction of the polarity. Simultaneously, the adsorption component exhibits a transition from a polarity-selective (P200-P400) to a porosity-selective (P500-P600) process, and displays no selectivity with P700 and AC in which the adsorptive saturation capacities are comparable to predicted values based on the monolayer surface coverage of molecule.
1,449 citations
TL;DR: A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements.
Abstract: A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches ∼0.9. The hydrogen-to-carbon (H/C, 1.4–1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, ∼0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R2 = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/O...
1,364 citations
TL;DR: This review critically assesses the contributions of carbon-based nanomaterials to a broad range of environmental applications: sorbents, high-flux membranes, depth filters, antimicrobial agents, environmental sensors, renewable energy technologies, and pollution prevention strategies.
Abstract: The unique and tunable properties of carbon-based nanomaterials enable new technologies for identifying and addressing environmental challenges. This review critically assesses the contributions of carbon-based nanomaterials to a broad range of environmental applications: sorbents, high-flux membranes, depth filters, antimicrobial agents, environmental sensors, renewable energy technologies, and pollution prevention strategies. In linking technological advance back to the physical, chemical, and electronic properties of carbonaceous nanomaterials, this article also outlines future opportunities for nanomaterial application in environmental systems.
1,343 citations
TL;DR: It was observed that inhibition to nitrifying organisms correlated with the fraction of Ag nanoparticles less than 5 nm in the suspension, and it appeared that these size nanoparticles could be more toxic to bacteria than any other fractions of nanoparticles or their counterpart bulk species.
Abstract: The intrinsic slow growth of nitrifying bacteria and their high sensitivity to environmental perturbations often result in cell growth inhibition by toxicants. Nanoparticles are of great concern to the environment because of their small size and high catalytic properties. This work sought to determine size-dependent inhibition by Ag nanoparticles and evaluate the relationship between the inhibition and reactive oxygen species (ROS). Nanoparticles with an average size range of 9−21 nm were synthesized by varying the molar ratios of BH4− /Ag+in the solution. The resulting ROS generation was quantified in the presence and absence of the bacteria while the degree of inhibition was inferred from specific oxygen uptake rate measurements, determined by extant respirometry. By examining the correlation between nanoparticle size distribution, photocatalytic ROS generation, intracellular ROS accumulation, and nitrification inhibition, we observed that inhibition to nitrifying organisms correlated with the fraction ...
1,248 citations
TL;DR: The CO2 emissions embodied in international trade among 87 countries for the year 2001 is determined and it is found that globally there are over 5.3 Gt of CO2 embodied in trade and that Annex B countries are net importers ofCO2 emissions.
Abstract: The flow of pollution through international trade flows has the ability to undermine environmental policies, particularly for global pollutants. In this article we determine the CO2 emissions embodied in international trade among 87 countries for the year 2001. We find that globally there are over 5.3 Gt of CO2 embodied in trade and that Annex B countries are net importers of CO2 emissions. Depending on country characteristics—such as size variables and geographic location—there are considerable variations in the embodied emissions. We argue that emissions embodied in trade may have a significant impact on participation in and effectiveness of global climate policies such as the Kyoto Protocol. We discuss several policy options to reduce the impact of trade in global climate policy. If countries take binding commitments as a part of a coalition, instead of as individual countries, then the impacts of trade can be substantially reduced. Adjusting emission inventories for trade gives a more consistent descr...
1,170 citations
TL;DR: This review summarizes the research progress of organic chemical adsorption on CNTs, and will provide useful information for CNT application and risk assessment.
Abstract: Carbon nanotubes (CNTs) have drawn special research attention because of their unique properties and potential applications. This review summarizes the research progress of organic chemical adsorption on CNTs, and will provide useful information for CNT application and risk assessment. Adsorption heterogeneity and hysteresis are two widely recognized features of organic chemical−CNT interactions. However, because different mechanisms may act simultaneously, mainly hydrophobic interactions, π−π bonds, electrostatic interactions, and hydrogen bonds, the prediction of organic chemical adsorption on CNTs is not straightforward. The dominant adsorption mechanism is different for different types of organic chemicals (such as polar and nonpolar), thus different models may be needed to predict organic chemical−CNT interaction. Adsorption mechanisms will be better understood by investigating the effects of properties of both CNTs and organic chemicals along with environmental conditions. Another major factor affec...
1,074 citations
TL;DR: The materials, architectures, performance, and energy efficiencies of these MEC systems that show promise as a method for renewable and sustainable energy production, and wastewater treatment are reviewed.
Abstract: The use of electrochemically active bacteria to break down organic matter, combined with the addition of a small voltage (>0.2 V in practice) in specially designed microbial electrolysis cells (MECs), can result in a high yield of hydrogen gas. While microbial electrolysis was invented only a few years ago, rapid developments have led to hydrogen yields approaching 100%, energy yields based on electrical energy input many times greater than that possible by water electrolysis, and increased gas production rates. MECs used to make hydrogen gas are similar in design to microbial fuel cells (MFCs) that produce electricity, but there are important differences in architecture and analytical methods used to evaluate performance. We review here the materials, architectures, performance, and energy efficiencies of these MEC systems that show promise as a method for renewable and sustainable energy production, and wastewater treatment.
TL;DR: It is suggested that dietary shift can be a more effective means of lowering an average household's food-related climate footprint than "buying local" and achieves more GHG reduction than buying all locally sourced food.
Abstract: Despite significant recent public concern and media attention to the environmental impacts of food, few studies in the United States have systematically compared the life-cycle greenhouse gas (GHG) emissions associated with food production against long-distance distribution, aka “food-miles.” We find that although food is transported long distances in general (1640 km delivery and 6760 km life-cycle supply chain on average) the GHG emissions associated with food are dominated by the production phase, contributing 83% of the average U.S. household’s 8.1 t CO2e/yr footprint for food consumption. Transportation as a whole represents only 11% of life-cycle GHG emissions, and final delivery from producer to retail contributes only 4%. Different food groups exhibit a large range in GHG-intensity; on average, red meat is around 150% more GHG-intensive than chicken or fish. Thus, we suggest that dietary shift can be a more effective means of lowering an average household’s food-related climate footprint than “buy...
TL;DR: The Fe3O4/HA was able to remove over 99% of Hg(LL) and Pb(ll) and over 95% of Cu(II) and Cd( II) in natural and tap water at optimized pH.
Abstract: Humic acid (HA) coated Fe3O4 nanciparticles (Fe3O4/HA) were developed for the removal of toxic Hg(II), Pb(II), Cd(II), and Cu(II) from water. Fe3O4/HA were prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TOC and XPS analysis showed the as-prepared Fe3O4/ HA contains similar to 11% (w/w) of HA which are fractions abundant in O and N-based functional groups. TEM images and laser particle size analysis revealed the Fe3O4/HA (with similar to 10 nm Fe3O4 cores) aggregated in aqueous suspensions to form aggregates with an average hydrodynamic size of similar to 140 nm. With a saturation magnetization of 79.6 emu/g, the Fe3O4/HA can be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the heavy metals to Fe3O4/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities from 46.3 to 97.7 mg/g. The Fe3O4/HA was stable in tap water, natural waters, and acidic/ basic solutions ranging from 0.1 M HCl to 2 M NaOH with low leaching of Fe (<= 3.7%) and HA (<= 5.3%). The Fe3O4/HA was able to remove over 99% of Hg(II) and Pb(II) and over 95% of COO and Cd(II) in natural and tap water at optimized pH. Leaching back of the Fe3O4/HA sorbed heavy metals in water was found to be negligible.
TL;DR: The phytotoxicity of ZnO nanoparticles was not directly from their limited dissolution in the bulk nutrient solution or rhizosphere, implying that little (if any) Zn O nanoparticles could translocate up in the ryegrass in this study.
Abstract: Increasing application of nanotechnology highlights the need to clarify nanotoxicity. However, few researches have focused on phytotoxicity of nanomaterials; it is unknown whether plants can uptake and transport nanoparticles. This study was to examine cell internalization and upward translocation of ZnO nanoparticles by Lolium perenne (ryegrass). The dissolution of ZnO nanoparticles and its contribution to the toxicity on ryegrass were also investigated. Zn2+ ions were used to compare and verify the root uptake and phytotoxicity of ZnO nanoparticles in a hydroponic culture system. The root uptake and phytotoxicity were visualized by light, scanning electron, and transmission electron microscopies. In the presence of ZnO nanoparticles, ryegrass biomass significantly reduced, root tips shrank, and root epidermal and cortical cells highly vacuolated or collapsed. Zn2+ ion concentrations in bulk nutrient solutions with ZnO nanoparticles were lower than the toxicity threshold of Zn2+ to the ryegrass; shoot Zn...
TL;DR: The bioaccumulation potential of perfluorinated acids with seven fluorinated carbons or less appears to be several orders of magnitude lower than "legacy" persistent lipophilic compounds classified as bioaccuulative.
Abstract: Perfluorinated acids, including perfluorinated carboxylates (PFCAs), and perfluorinated sulfonates (PFASs), are environmentally persistent and have been detected in a variety of wildlife across the globe. The most commonly detected PFAS, perfluorooctane sulfonate (PFOS), has been classified as a persistent and bioaccumulative substance. Similarities in chemical structure and environmental behavior of PFOS and the PFCAs that have been detected in wildlife have generated concerns about the bioaccumulation potential of PFCAs. Differences between partitioning behavior of perfluorinated acids and persistent lipophilic compounds complicate the understanding of PFCA bioaccumulation and the subsequent classification of the bioaccumulation potential of PFCAs according to existing regulatory criteria. Based on available research on the bioaccumulation of perfluorinated acids, five key points are highlighted in this review: (1) bioconcentration and bioaccumulation of perfluorinated acids are directly related to the ...
TL;DR: A spatially explicit and structurally detailed SPARROW water-quality model reveals important differences in the sources and transport processes that control nitrogen (N) and phosphorus (P) delivery to the Gulf of Mexico and indicates the diversity of management approaches required to achieve efficient control of nutrient loads.
Abstract: Seasonal hypoxia in the northern Gulf of Mexico has been linked to increased nitrogen fluxes from the Mississippi and Atchafalaya River Basins, though recent evidence shows that phosphorus also influences productivity in the Gulf. We developed a spatially explicit and structurally detailed SPARROW water-quality model that reveals important differences in the sources and transport processes that control nitrogen (N) and phosphorus (P) delivery to the Gulf. Our model simulations indicate that agricultural sources in the watersheds contribute more than 70% of the delivered N and P. However, corn and soybean cultivation is the largest contributor of N (52%), followed by atmospheric deposition sources (16%); whereas P originates primarily from animal manure on pasture and rangelands (37%), followed by corn and soybeans (25%), other crops (18%), and urban sources (12%). The fraction of in-stream P and N load delivered to the Gulf increases with stream size, but reservoir trapping of P causes large local- and re...
TL;DR: The results demonstrate that high hydrogen recovery and production rates are possible in a single chamber MEC without a membrane, potentially reducing the costs of these systems and allowing for new and simpler designs.
Abstract: Hydrogen gas can be produced by electrohydrogenesis in microbial electrolysis cells (MECs) at greater yields than fermentation and at greater energy efficiencies than water electrolysis. It has been assumed that a membrane is needed in an MEC to avoid hydrogen losses due to bacterial consumption of the product gas. However, high cathodic hydrogen recoveries (78 ± 1% to 96 ± 1%) were achieved in an MEC despite the absence of a membrane between the electrodes (applied voltages of 0.3 < Eap < 0.8 V; 7.5 mS/cm solution conductivity). Through the use of a membrane-less system, a graphite fiber brush anode, and close electrode spacing, hydrogen production rates reached a maximum of 3.12 ± 0.02 m3 H2/m3 reactor per day (292 ± 1 A/m3) at an applied voltage of Eap = 0.8 V. This production rate is more than double that obtained in previous MEC studies. The energy efficiency relative to the electrical input decreased with applied voltage from 406 ± 6% (Eap = 0.3 V) to 194 ± 2% (Eap = 0.8 V). Overall energy efficienc...
TL;DR: Results show that hollow spheres can be more readily separated from the slurry system by filtration or sedimentation after photocatalytic reaction and reused than conventional powder photocatalyst, confirming ZnO hollow spheres is stability and not photocorroded.
Abstract: ZnO hollow spheres with porous crystalline shells were one-pot fabricated by hydrothermal treatment of glucose/ZnCl2 mixtures at 180 °C for 24 h, and then calcined at different temperatures for 4 h. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption−desorption isotherms. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of Rhodamine B aqueous solution at ambient temperature. The results indicated that the average crystallite size, shell thickness, specific surface areas, pore structures, and photocatalytic activity of ZnO hollow spheres could be controlled by varying the molar ratio of glucose to zinc ions (R). With increasing R, the photocatalytic activity increases and reaches a maximum value at R = 15, which can be attributed to the combined effects of several factors such as specific surface area, the porous structure and the crystallite size. Further...
TL;DR: The bactericidal effect of nano-Fe0 was a unique property of nano -Fe0, which was not observed in other types of iron-based compounds, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron.
Abstract: Zero-valent iron nanoparticles (nano-Fe0) in aqueous solution rapidly inactivated Escherichia coli. A strong bactericidal effect of nano-Fe0 was found under deaerated conditions, with a linear correlation between log inactivation and nano-Fe0 dose (0.82 log inactivation/mg/L nano-Fe0·h). The inactivation of E. coli under air saturation required much higher nano-Fe0 doses due to the corrosion and surface oxidation of nano-Fe0 by dissolved oxygen. Significant physical disruption of the cell membranes was observed in E. coli exposed to nano-Fe0, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron. The reaction of Fe(II) with intracellular oxygen or hydrogen peroxide also may have induced oxidative stress by producing reactive oxygen species. The bactericidal effect of nano-Fe0 was a unique property of nano-Fe0, which was not observed in other types of iron-based compounds.
TL;DR: Life cycle GHG emissions from PHEVs are assessed and it is found that they reduceGHG emissions by 32% compared to conventional vehicles, but have small reductions compared to traditional hybrids.
Abstract: Plug-in hybrid electric vehicles (PHEVs), which use electricity from the grid to power a portion of travel, could play a role in reducing greenhouse gas (GHG) emissions from the transport sector. However, meaningful GHG emissions reductions with PHEVs are conditional on low-carbon electricity sources. We assess life cycle GHG emissions from PHEVs and find that they reduce GHG emissions by 32% compared to conventional vehicles, but have small reductions compared to traditional hybrids. Batteries are an important component of PHEVs, and GHGs associated with lithium-ion battery materials and production account for 2–5% of life cycle emissions from PHEVs. We consider cellulosic ethanol use and various carbon intensities of electricity. The reduced liquid fuel requirements of PHEVs could leverage limited cellulosic ethanol resources. Electricity generation infrastructure is long-lived, and technology decisions within the next decade about electricity supplies in the power sector will affect the potential for l...
TL;DR: The current energy consumption of different desalination processes is reviewed and a comparison with other common energy-consuming ventures leads to some interesting conclusions.
Abstract: Water, energy, and environmental issues are closely related. New water techniques consume energy, and innovative renewable energy techniques using biofuels and biodiesel consume an incredible amount of water. Different desalination techniques that consume different energy levels from different sources are in use today. Some people, environmentalists, decision makers, and even scientists, mainly in nonscientific publications, consider energy consumption in desalination to be too high and are seeking new ways of reducing it, which often involves increasing capital investment. Efforts should be directed at reducing not only energy consumption but also total water cost. A competent grasp of thermodynamics and heat and mass transfer theory, as well as a proper understanding of current desalination processes, is essential for ensuring beneficial improvements in desalination processes. Thermodynamics sets the absolute minimum limit of the work energy required to separate water from a salt solution. Unavoidable i...
TL;DR: The oxidation of methanol, ethanol, 2-propanol, and benzoic acid by the reaction of nanoparticulate zero-valent iron (nZVI) or ferrous iron (Fe[II]) with O2 in the absence of ligands was studied.
Abstract: The corrosion of zero-valent iron (Fe0(s)) by oxygen (O2) can lead to the oxidation of organic compounds. To gain insight into the reaction mechanism and to assess the nature of the oxidant, the oxidation of methanol, ethanol, 2-propanol, and benzoic acid by the reaction of nanoparticulate zero-valent iron (nZVI) or ferrous iron (Fe[II]) with O2 in the absence of ligands was studied. At pH values below 5, Fe0(s) nanoparticles were oxidized by O2 within 30 min with a stoichiometry of approximately two Fe0(s) oxidized per O2 consumed. The yield of methanol and ethanol oxidation products increased from 1% at acidic pH to 6% at pH 7, relative to nZVI added. Product yields from 2-propanol and benzoic acid were highest under acidic conditions, with little oxidation observed at neutral pH. At pH values below 5, product formation was attributable to hydroxyl radical (OH·) production through the Fenton reaction, involving hydrogen peroxide and Fe(II) produced during nZVI oxidation. At higher pH values, the oxidati...
TL;DR: Point-of-use (POU) water treatment technology has emerged as an approach that empowers people and communities without access to safe water to improve water quality by treating it in the home as discussed by the authors.
Abstract: The lack of safe water creates a tremendous burden of diarrheal disease and other debilitating, life-threatening illnesses for people in the developing world. Point-of-use (POU) water treatment technology has emerged as an approach that empowers people and communities without access to safe water to improve water quality by treating it in the home. Several POU technologies are available, but, except for boiling, none have achieved sustained, large-scale use. Sustained use is essential if household water treatment technology (HWT) is to provide continued protection, but it is difficult to achieve. The most effective, widely promoted and used POU HWTs are critically examined according to specified criteria for performance and sustainability. Ceramic and biosand household water filters are identified as most effective according to the evaluation criteria applied and as having the greatest potential to become widely used and sustainable for improving household water quality to reduce waterborne disease and death.
TL;DR: The global potential for bioenergy on abandoned agriculture lands is shown to be less than 8% of current primary energy demand, based on historical land use data, satellite-derived land cover data, and global ecosystem modeling.
Abstract: Converting forest lands into bioenergy agriculture could accelerate climate change by emitting carbon stored in forests, while converting food agriculture lands into bioenergy agriculture could threaten food security. Both problems are potentially avoided by using abandoned agriculture lands for bioenergy agriculture. Here we show the global potential for bioenergy on abandoned agriculture lands to be less than 8% of current primary energy demand, based on historical land use data, satellite-derived land cover data, and global ecosystem modeling. The estimated global area of abandoned agriculture is 385-472 million hectares, or 66-110% of the areas reported in previous preliminary assessments. The area-weighted mean production of above-ground biomass is 4.3 tons ha(-1) y(-1), in contrast to estimates of up to 10 tons ha(-1) y(-1) in previous assessments. The energy content of potential biomass grown on 100% of abandoned agriculture lands is less than 10% of primary energy demand for most nations in North America, Europe, and Asia, but it represents many times the energy demand in some African nations where grasslands are relatively productive and current energy demand is low.
TL;DR: A linear regression model of the carbonaceous particulate mass in the submicrometer size range CM(PM1) as a function of aerosol light absorption properties measured by the aethalometer is introduced, and results indicate that light absorption exponents of 1.8-1.9 for wood burning calculated from the light absorption at 470 and 950 nanometers should be used to obtain agreement of the two methods regarding the relative wood burning and traffic emission contributions.
Abstract: A source apportionment study was performed for particulate matter in the small village of Roveredo, Switzerland, where more than 70% of the households use wood burning for heating purposes. A two-lane trans-Alpine highway passes through the village and contributes to the total aerosol burden in the area. The village is located in a steep Alpine valley characterized by strong and persistent temperature inversions during winter, especially from December to February. During two winter and one early spring campaigns, a seven-wavelength aethalometer, high volume (HIVOL) samplers, an Aerodyne quadrupole aerosol mass spectrometer (AMS), an optical particle counter (OPC), and a Sunset Laboratory OCEC analyzer were deployed to study the contribution of wood burning and traffic aerosols to particulate matter. A linear regression model of the carbonaceous particulate mass in the submicrometer size range CM(PM1) as a function of aerosol light absorption properties measured by the aethalometer is introduced to estimate the particulate mass from wood burning and traffic (PM(wb), PM(traffic)). This model was calibrated with analyses from the 14C method using HIVOL filter measurements. These results indicate that light absorption exponents of 1.1 for traffic and 1.8-1.9 for wood burning calculated from the light absorption at 470 and 950 nanometers should be used to obtain agreement of the two methods regarding the relative wood burning and traffic emission contributions to CM(PM1) and also to black carbon. The resulting PM(wb) and PM(traffic) values explain 86% of the variance of the CM(PM1) and contribute, on average, 88 and 12% to CM(PM1), respectively. The black carbon is estimated to be 51% due to wood burning and 49% due to traffic emissions. The average organic carbon/total carbon (OC/TC) values were estimated to be 0.52 for traffic and 0.88 for wood burning particulate emissions.
TL;DR: It is demonstrated that a greatly increased bioavailability of As under the flooded conditions is the main reason for an enhanced As accumulation by flooded rice, and growing rice aerobically can dramatically decrease the As transfer from soil to grain.
Abstract: Arsenic (As) exposure from consumption of rice can be substantial, particularly for the population on a subsistence rice diet in South Asia. Paddy rice has a much enhanced As accumulation compared with other cereal crops, and practical measures are urgently needed to decrease As transfer from soil to grain. We investigated the dynamics of As speciation in the soil solution under both flooded and aerobic conditions and compared As accumulation in rice shoot and grain in a greenhouse experiment. Flooding of soil led to a rapid mobilization of As, mainly as arsenite, in the soil solution. Arsenic concentrations in the soil solution were 7−16 and 4−13 times higher under the flooded than under the aerobic conditions in the control without As addition and in the +As treatments (10 mg As kg−1 as arsenite or arsenate), respectively. Arsenate was the main As species in the aerobic soil. Arsenic accumulation in rice shoots and grain was markedly increased under flooded conditions; grain As concentrations were 10−15...
TL;DR: The comparison of the internal resistances of the two air cathode systems indicates that the much lower resistances, including anode, cathode, and membrane resistance, contributed to the much better performance of the single- chamber MFCs than the two-chamber system.
Abstract: Identifying the limiting factors in a microbial fuel cell (MFC) system requires qualifying the contribution of each component of an MFC to internal resistance. In this study, a new method was developed to calculate the internal resistance distribution of an MFC. Experiments were conducted to identify the limiting factors in single-chamber MFCs by varying the anode surface areas, cathode surface areas, and phosphate buffer concentrations. For the MFCs with equally sized electrodes (7 cm2) and 200 mM phosphate buffer, the anode contributed just 5.4% of the internal resistance, while the cathode and the electrolyte each contributed 47.3%, indicating that the anode was not the limiting factor in power generation. The limitation of the cathode was further revealed by the 780% higher area-specific resistance (284.4 Ω cm2) than the 32.3 Ω cm2 of the anode. The electrolyte limitation was also evidenced by the greatly increased contribution of electrolyte in internal resistance from 47.3 to 78.2% when the concentr...
TL;DR: A mechanism for the enhanced reactivity is proposed in which electrons are shuttled from TiO2 particles to the SWCNTs as a result of an optimalTiO2/ CNT arrangement that stabilizes charge separation and reduces charge recombination.
Abstract: Electron−hole recombination limits the efficiency of TiO2 photocatalysis. We have investigated the efficacy with which anatase/carbon nanotube (CNT) composite materials reduce charge recombination and enhance reactivity. We synthesized nanostructured assemblies composed of different proportions of anatase (5 or 100 nm) and either single-or multi-walled CNTs. The composites were prepared using a simple low temperature process in which CNTs and anatase nanoparticles were dispersed in water, dehydrated at 80 °C, and dried at 104 °C. The structures of the various TiO2/CNT composites were characterized by scanning electron microscopy (SEM) and their function was tested by phenol oxidation. Charge recombination was compared by measuring the photoluminescence spectra of select composites. We found that a nanostructured composite assembled from the 100 nm anatase and single-walled CNTs (SWCNTs) exhibited enhanced and selective photocatalytic oxidation of phenol in comparison to both pure anatase and Degussa P25. ...
TL;DR: In general, compounds that contain an iodo-group have enhanced mammalian cell cytotoxicity and genotoxicity as compared to their brominated and chlorinated analogues.
Abstract: An occurrence study was conducted to measure five iodo-acids (iodoacetic acid, bromoiodoacetic acid, (Z)-3-bromo-3-iodo-propenoic acid, (E)-3-bromo-3-iodo-propenoic acid, and (E)-2-iodo-3-methylbutenedioic acid) and two iodo-trihalomethanes (iodo-THMs), (dichloroiodomethane and bromochloroiodomethane) in chloraminated and chlorinated drinking waters from 23 cities in the United States and Canada. Since iodoacetic acid was previouslyfound to be genotoxic in mammalian cells, the iodo-acids and iodo-THMs were analyzed for toxicity. A gas chromatography (GC)/negative chemical ionization-mass spectrometry (MS) method was developed to measure the iodo-acids; iodo-THMs were measured using GC/high resolution electron ionization-MS with isotope dilution. The iodo-acids and iodo-THMs were found in waters from most plants, at maximum levels of 1.7 microg/L (iodoacetic acid), 1.4 microg/L (bromoiodoacetic acid), 0.50 microg/L ((Z)-3-bromo-3-iodopropenoic acid), 0.28 microg/L ((E)-3-bromo-3-iodopropenoic acid), 0.58 microg/L ((E)-2-iodo-3-methylbutenedioic acid), 10.2 microg/L (bromochloroiodomethane), and 7.9 microg/L (dichloroiodomethane). Iodo-acids and iodo-THMs were highest at plants with short free chlorine contact times ( 45 min). Iodide levels in source waters ranged from 0.4 to 104.2 microg/L (when detected), but there was not a consistent correlation between bromide and iodide. The rank order for mammalian cell chronic cytotoxicity of the compounds measured in this study, plus other iodinated compounds, was iodoacetic acid > (E)-3-bromo-2-iodopropenoic acid > iodoform > (E)-3-bromo-3-iodo-propenoic acid > (Z)-3-bromo-3-iodo-propenoic acid > diiodoacetic acid > bromoiodoacetic acid > (E)-2-iodo-3-methylbutenedioic acid > bromodiiodomethane > dibromoiodomethane > bromochloroiodomethane approximately chlorodiiodomethane > dichloroiodomethane. With the exception of iodoform, the iodo-THMs were much less cytotoxic than the iodo-acids. Of the 13 compounds analyzed, 7 were genotoxic; their rank order was iodoacetic acid >> diiodoacetic acid > chlorodiiodomethane > bromoiodoacetic acid > E-2-iodo-3-methylbutenedioic acid > (E)-3-bromo-3-iodo-propenoic acid > (E)-3-bromo-2-iodopropenoic acid. In general, compounds that contain an iodo-group have enhanced mammalian cell cytotoxicity and genotoxicity as compared to their brominated and chlorinated analogues.
TL;DR: It was evident that electron-donating substitution on the aromatic rings strengthened the pi-pi interaction between the aromatics and CNTs and thus the adsorption affinity, which will advance the understanding of the sorption behavior of C NTs in the environmental systems.
Abstract: With increasing production and application of carbon nanotubes (CNTs), it becomes necessary to understand the interaction between CNTs and aromatic compounds, an important group of organic contaminants and structural components of large organic molecules in biological systems. However, so far few experimental studies have been conducted to systematically investigate the sorption mechanism of polar aromatics to CNTs. Therefore, cyclohexanol, phenol, catechol, pyrogallol, 2-phenylphenol, 1-naphthol, and naphthalene were selected to investigate the role of aromatic structure and -OH substitution in the polar aromatics-CNTs system. Sorption affinity of these compounds by CNTs increased with increasing number of aromatic rings, with an order of cyclohexanol < phenol < 2-phenylphenol < 1-naphthol, and was greatly enhanced by -OH substitution, with an order of phenol (1 -OH) < catechol (2 -OH) < pyrogallol(3-OH). Four possible solute-sorbent interactions, i.e., hydrophobic effect, electrostatic interaction, hydrogen bonding, and pi-pi bonds, were discussed to addressthe underlying mechanism of the enhanced sorption affinity by -OH substitution. It was evident that electron-donating substitution on the aromatic rings strengthened the pi-pi interaction between the aromatics and CNTs and thus the adsorption affinity. These results will advance the understanding of the sorption behavior of CNTs in the environmental systems.