Showing papers in "Environmental Science & Technology in 2000"
TL;DR: As they persist, or age, in soil, organic compounds become progressively less available for uptake by organisms, for exerting toxic effects, and for biodegradation and bioremediation by microorganisms.
Abstract: As they persist, or age, in soil, organic compounds become progressively less available for uptake by organisms, for exerting toxic effects, and for biodegradation and bioremediation by microorganisms. This declining bioavailability is not reflected by currently used methods for the chemical analysis of soils for determining concentrations of organic pollutants. As a result, such methods overestimate exposure, and thus risk, from toxic chemicals in contaminated sites.
1,305 citations
TL;DR: In this article, Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter.
Abstract: Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter. The material is stable in air once it has dried and contains 22.6% iron by weight. The supported zero-valent iron nanoparticles (“Ferragels”) rapidly separate and immobilize Cr(VI) and Pb(II) from aqueous solution, reducing the chromium to Cr(III) and the Pb to Pb(0) while oxidizing the Fe to goethite (α-FeOOH). The kinetics of the reduction reactions are complex and include an adsorption phase. About 10% of the iron in the material appears to be located at active surface sites. Once these sites have been saturated, the reduction process continues but at a much lower rate, which is likely limited by mass transfer. Rates of remediation of Cr(VI) and Pb(II) are up to 30 times higher for Ferragels than for iron filings or iron powder on a (Fe) molar basis. Over 2 months, reduction of Cr(VI) was 4.8 times greater for Ferragels than for an equal weigh...
1,137 citations
TL;DR: In this article, a large variability is observed among the reported values that could be used to predict metal mobility and bioavailability, and a semi-mechanistic model based on the competitive adsorption of metamodel was proposed.
Abstract: Environmental risk assessment of metals depends to a great extent on modeling the fate and the mobility of metals based on soil−liquid partitioning coefficients. A large variability is observed among the reported values that could be used to predict metal mobility and bioavailability. To evaluate this, soil−liquid partitioning coefficients (Kd) for many elements but especially for the metals cadmium, copper, lead, nickel, and zinc were compiled from over 70 studies of various origins collected from the literature. The relationships between the reported values are explored relative to variations in soil solution pH, soil organic matter (SOM), and concentrations of total soil metal. The results of multiple linear regressions show that Kd values are best predicted using empirical linear regressions with pH (with R 2 values of 0.29−0.58) or with pH and either the log of SOM or the log of total metal and with resulting R 2 values of 0.42−0.76. A semi-mechanistic model based on the competitive adsorption of met...
1,066 citations
TL;DR: In this article, an analytical method involving analyte extraction with a Carbograph 4 cartridge and LC coupled with negative turbo ion spray tandem mass spectrometry in the selected reaction monitoring mode was developed.
Abstract: Sewage treatment plant (STP) effluents with primarily domestic inputs are strongly suspected to be an important source of natural and synthetic estrogens contaminating the aquatic environment. Even a few ng/L of some of these substances can provoke reproductive disturbances in riverine fish. The main purpose of this investigation has been that of ascertaining whether activated sludge STPs (ASSTPs) are able to produce significant amounts of free estrogens. For this purpose, we have monitored monthly estriol (E3), estradiol (E2), estrone (E1) and ethinylestradiol (EE2) in influents and effluents of six Roman ASSTPs for five months. To do this, we have developed an original analytical method involving analyte extraction with a Carbograph 4 cartridge and LC coupled with negative turbo ion spray tandem mass spectrometry in the selected reaction monitoring mode. Analyte recovery ranged between 86 and 91%, and limits of quantification were below 1 ng/L. Over five months, inlet concentrations of E3, E2, E1 and EE...
979 citations
TL;DR: Contingent valuation (CV) is a survey-based method frequently used for placing monetary values on environmental goods and services not bought and sold in the marketplace as discussed by the authors, and it is usually the only feasible method for including passive-use considerations in an economic analysis, a practice that has engendered considerable controversy.
Abstract: Contingent valuation (CV) is a survey-based method frequently used for placing monetary values on environmental goods and services not bought and sold in the marketplace. CV is usually the only feasible method for including passive-use considerations in an economic analysis, a practice that has engendered considerable controversy. The issue of what a CV study tries to value is first addressed from the perspective of a policy-maker, and then the controversy over the inclusion of passive-use is taken up in more detail. The major issues and positions taken in the technical debate over the use of CV are summarized from a user's perspective. Key design and implementation issues involved in undertaking a CV survey are examined, and the reader is provided with a set of factors to examine in assessing the quality of a CV study.
848 citations
TL;DR: In this article, the performance of a thin-film composite aromatic polyamide nanofiltration membrane and its relation to membrane surface charge (electrokinetic) characteristics were investigated.
Abstract: The performance (i.e., water flux and solute rejection) of a thin-film composite aromatic polyamide nanofiltration membrane and its relation to membrane surface charge (electrokinetic) characteristics were investigated. Membrane performance and streaming potential measurements were carried out as a function of pH for several solution chemistries, including an indifferent electrolyte, humic acid, and anionic and cationic surfactants. Performance results for the membrane were interpreted by relating the water flux and salt/ion rejection to the membrane charge characteristics. In the case of the indifferent electrolyte (NaCl), water flux and salt passage were maximal at the membrane pore isoelectric point (pH 5) primarily due to decreased electrostatic repulsion and increased pore volume (size) in the cross-linked polymer network. Ion rejection is directly related to the membrane pore charge and is attributed to co-ion electrostatic repulsion (exclusion). At low pH, negative rejection of protons was observed...
659 citations
TL;DR: In this paper, a modified Langmuir−Hinshelwood−Hougen−Watson (LHHW) kinetic model was used to investigate the pathways and kinetics through which chlorinated ethylenes and their daughter products react with Fe(0) particles.
Abstract: Pathways and kinetics through which chlorinated ethylenes and their daughter products react with Fe(0) particles were investigated through batch experiments. Substantial intra- and interspecies inhibitory effects were observed, requiring the use of a modified Langmuir−Hinshelwood−Hougen−Watson (LHHW) kinetic model in which species compete for a limited number of reactive sites at the particle−water interface. Results indicate that reductive β-elimination accounts for 87% of tetrachloroethylene (PCE), 97% of trichloroethylene (TCE), 94% of cis-dichloroethylene (cis-DCE), and 99% of trans-dichloroethylene (trans-DCE) reaction. Reaction of 1,1-DCE gives rise to ethylene, consistent with a reductive α-elimination pathway. For the highly reactive chloro- and dichloroacetylene intermediates produced from the reductive elimination of TCE and PCE, 100% and 76% of the reaction, respectively, occur via hydrogenolysis to lesser chlorinated acetylenes. The branching ratios for reactions of PCE or TCE (and their daugh...
635 citations
TL;DR: In this article, the state of the art on their sampling and analytical procedures are commented, and the influence of the fuel, fossil and nonfossil fuels, the combustor type and the combustion variables are analyzed concerning polycyclic aromatic hydrocarbons (PAH) formation and emission in solid/gaseous phase.
Abstract: Polycyclic aromatic hydrocarbons (PAH) emitted from fluidized bed combustion have been reviewed. Firstly, the PAH origin is undertaken. Secondly, the state of the art on their sampling and analytical procedures are commented. Finally, the influence of the fuel, fossil and nonfossil fuels, the combustor type and the combustion variables are analyzed concerning PAH formation and emission in solid/gaseous phase.
598 citations
TL;DR: In this article, residential wood combustion emissions were analyzed to determine emission rates and to develop chemical emissions profiles that represent the appliances and woods typically used in wood-burning communities, over 350 elements, inorganic compounds, and organic compounds were quantified.
Abstract: Residential wood combustion emissions were analyzed to determine emission rates and to develop chemical emissions profiles that represent the appliances and woods typically used in wood-burning communities. Over 350 elements, inorganic compounds, and organic compounds were quantified. A range of 4−9 g/kg dry fuel of particulate matter (<2.5 μm) and 5−22 g/kg volatile organic compounds were observed. Samples were collected using a dilution stack sampler equipped with a 2.5-μm particle selective cyclone. Emissions were diluted 20−70 times, cooled to ambient temperature, and allowed 80 s for condensation prior to collection. Wood type, wood moisture, burn rate, and fuel load were varied for different experiments. Fine particle and semivolatile organic compounds were collected on filter/PUF/XAD/PUF cartridges. Inorganic samples and mass were collected on Teflon and quartz filters. Volatile organic carbon compounds were trapped with Tenax (C8−C20), canister (C2−C12), and 2,4-dinitrophenylhydrazine impregnated ...
585 citations
TL;DR: In this paper, two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers, and they were applied to data collected in California's San Joaquin Valley during two severe wintertime air pollution episodes.
Abstract: Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contributions to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbons and particle-phase organic compounds as tracers to determine source contributions to non-methane organic gases in the atmosphere. Both models are applied to data collected in California's San Joaquin Valley during two severe wintertime air pollution episodes. Source contributions to fine particle air quality are calculated for two urban sites, Fresno and Bakersfield, and one background site, Kern Wildlife Refuge. Primary particle emissions from hardwood combustion, softwood combustion, diesel engines, meat cooking, and gasoline-powered motor vehicles contribute on average 79% of the airborne fine particle organic compound mass at the urban sites during both episodes with smaller but still measurable contributions from fine particle road dust and natural gas combustion aerosol. Anthropogenic primary particle sources contribute less than 10% of the fine particle mass concentration at the background site. The combined gas-phase and particle-phase organic compound receptor model shows that gasoline-powered motor vehicle exhaust and gasoline vapors are the largest contributors to non-methane organic gases concentrations followed by natural gas leakage. Smaller but statistically significant contributions to organic vapors from wood combustion, meat cooking, and diesel exhaust also are quantified.
570 citations
TL;DR: In this article, a brake wear study was performed using seven brake pad formulations that were in high volume use in 1998, including semi-metallic brakes, brakes using potassium titanate fibers, and brakes using aramid fibers.
Abstract: Current particulate matter (PM) emission factor models estimate brake wear particulate matter emission rates using data derived from asbestos brakes. However, most brake pads are now produced from nonasbestos materials. Little work has been performed on emissions from brakes using these materials. Therefore, a brake wear study was performed using seven brake pad formulations that were in high volume use in 1998. Included were semi-metallic brakes, brakes using potassium titanate fibers, and brakes using aramid fibers. Brakes were tested on a brake dynamometer under four wear conditions. On average, 35% of the brake pad mass loss was emitted as airborne PM. The observed wear rates correspond to vehicle emission rates of 5.1−14.1 mg/mi. On average, 86 and 63% of the airborne PM was smaller than 10 μm in diameter (PM10) or 2.5 μm in diameter (PM2.5), respectively. The large number of particles observed in some wear tests was attributed to condensation, a process that is highly dependent on dilution condition...
TL;DR: In this article, a new hydrate-based gas separation (HBGS) process was developed for recovering CO2 from flue gas, where Tetrahydrofuran (THF) was chosen as a hydrate promoter.
Abstract: The main purpose of this study was to develop a new hydrate-based gas separation (HBGS) process especially for recovering CO2 from flue gas. Temperature and pressure conditions for hydrate formation have been closely examined at the various CO2 concentrations of flue gases. Tetrahydrofuran (THF) chosen as a hydrate promoter can also participate in forming hydrates and produces a mixed hydrate together with CO2. The hydrate stability region was greatly expanded by using THF for lowering the equilibrium formation pressure. To confirm thermodynamic validity of the HBGS process, the three-phase equilibria of hydrate, liquid, and vapor were measured for the systems comprising CO2, N2 and water with or without THF in the temperature range of 272−295 K. In addition, two phase equilibria of hydrate and vapor were experimentally investigated for the same systems at several temperatures. Through close examination of the overall experimental results, it was firmly verified that the HBGS process makes it possible to ...
TL;DR: The recent identification of one class of fluorinated surfactants in groundwater impacted by fire-fighting activity has created an awareness of the potential environmental issues resulting from the firefighting activity as mentioned in this paper.
Abstract: The recent identification of one class of fluorinated surfactants in groundwater impacted by fire-fighting activity has created an awareness of the potential environmental issues resulting from the...
TL;DR: An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described in this paper, which is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds.
Abstract: An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described. The method, named electro-Fenton, is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds. An industrial pollutant, p-nitrophenol (PNP), was chosen for this study and was eventually mineralized. The major intermediary degradation products such as hydroquinone, benzoquinone, 4-nitrocatechol, 1,2,4-trihydroxybenzene and 3,4,5-trihydroxy- nitrobenzene were unequivocally identified by HPLC and GC-MS methods. The rate constants of the hydroxylation reactions were determined. The mineralization of the initial pollutant and the intermediates formed during electro-Fenton treatment was followed by total organic carbon (TOC) analyses. Dependence of mineralization on the amount of electrical energy consumed is shown by the relative decrease of TOC values. A mineralization reaction mechanism is proposed.
TL;DR: In this article, the authors used the Pitzer method to define pH for calibration of glass membrane electrodes in mine waters with pH values as low as −3.6 and total dissolved metal concentrations as high as 200 g/L.
Abstract: Extremely acidic mine waters with pH values as low as −3.6, total dissolved metal concentrations as high as 200 g/L, and sulfate concentrations as high as 760 g/L, have been encountered underground in the Richmond Mine at Iron Mountain, CA. These are the most acidic waters known. The pH measurements were obtained by using the Pitzer method to define pH for calibration of glass membrane electrodes. The calibration of pH below 0.5 with glass membrane electrodes becomes strongly nonlinear but is reproducible to a pH as low as −4. Numerous efflorescent minerals were found forming from these acid waters. These extreme acid waters were formed primarily by pyrite oxidation and concentration by evaporation with minor effects from aqueous ferrous iron oxidation and efflorescent mineral formation.
TL;DR: In this paper, a dilution source sampling system is augmented to measure the size-distributed chemical composition of fine particle emissions from motor vehicles using optical particle counter (OPC), a differential mobility analyzer (DMA)/condensation nucleus counter (CNC) combination, and a pair of microorifice uniform deposit impactors (MOUDIs).
Abstract: A dilution source sampling system is augmented to measure the size-distributed chemical composition of fine particle emissions from motor vehicles. Measurements are made using an optical particle counter (OPC), a differential mobility analyzer (DMA)/condensation nucleus counter (CNC) combination, and a pair of microorifice uniform deposit impactors (MOUDIs). The sources tested with this system include catalyst-equipped gasoline-powered light-duty vehicles, noncatalyst gasoline-powered light-duty vehicles, and medium-duty diesel trucks. Chemical composition analysis demonstrates that particles emitted from the gasoline-powered vehicles tested are largely composed of organic compounds while particles emitted from diesel engines contain roughly equal amounts of organic compounds and elemental carbon. The particle mass distributions from all mobile sources tested have a single mode that peaks at approximately 0.1−0.2 μm particle diameter. Of the two diesel vehicles tested, the vehicle with the lowest fine particle emissions rate released the largest number of ultrafine particles, a finding similar to that of Bagley et al. (Characterization of fuel and aftertreatment device effects on diesel emissions; Technical Report 76; Health Effects Institute: Cambridge, MA, 1996). Particle size distribution measurements taken throughout the FTP urban driving cycle used to test all of the vehicles described in this paper reveal that particulate mass emission rates and particulate size distributions from the vehicles tested here are similar during the cold start and hot start segments of the driving cycle.
TL;DR: In this article, a series of experiments were conducted to ascertain the effects of differing environmental conditions on estrogen partitioning to sediment, and the sorption of estrogen to sediments correlated with total organic carbon content.
Abstract: Natural and synthetic steroid estrogens have been detected in sewage treatment work effluents discharged into rivers. An understanding of the partitioning of these estrogens between water and sediment is critical for the prediction of their fates in river systems. Hence, a series of experiments was conducted to ascertain the effects of differing environmental conditions on estrogen partitioning to sediment. Fugacity level 1 (sediment phase) output data demonstrated a good correlation with removal of estrogens from the water phase. Synthetic estrogens, with their higher Kow values, were removed more readily from the water phase than the natural estrogens. Maximum sorption to the sediment phase was attained after 1 h of shaking. At higher estrogen concentrations, there was a decrease in estrogen removal, while higher levels of sediment induced greater removal. The sorption of estrogen to sediments correlated with total organic carbon content. However, the presence of organic carbon was not a prerequisite fo...
TL;DR: In this paper, the authors show that the concept of normalizing element concentrations to an average total crust value is of doubtful merit, for theoretical considerations alone, due to the variable composition of the Earth's crust at any given point compared to the global average, the natural fractionation of elements during their transfer from the crust to the atmosphere through processes such as weathering and winnowing of fines, and the differential solubility of minerals in weak chemical digestions generally used in environmental studies.
Abstract: The popular concept of enrichment factors (EFs) as a means of identifying and quantifying human interference with global element cycles is evaluated. It is demonstrated that the concept of normalizing element concentrations to an average total crust value is of doubtful merit, for theoretical considerations alone. Serious flaws with EFs include the variable composition of the Earth's crust at any given point compared to the global average, the natural fractionation of elements during their transfer from the crust to the atmosphere through processes such as weathering and winnowing of fines, and the differential solubility of minerals in the weak chemical digestions generally used in environmental studies. Furthermore the impact of biogeochemical processes is neglected. A biomonitoring survey of atmospheric chemistry over a 1.5 million km2 area in northern Europe is used to show that EFs are governed here by completely different processes than anthropogenic activities. As a simple means to assess the maxim...
TL;DR: The increasing vehicle traffic associated with urban sprawl in the United States is frequently linked to degradation of air quality, but its effect on aquatic sediment is less well-recognized.
Abstract: The increasing vehicle traffic associated with urban sprawl in the United States is frequently linked to degradation of air quality, but its effect on aquatic sediment is less well-recognized. This...
TL;DR: In this article, the authors describe a study that compared exhaust emissions from in-use heavy trucks fueled with a biodiesel blend with those from trucks fuelled with petroleum diesel, a blend designated as B35.
Abstract: Biodiesel, a fuel that can be made from renewable biological sources such as vegetable oils or animal fats, has been recognized recently as an environment friendly alternative fuel for diesel engines. In this paper, we describe a study that compared exhaust emissions from in-use heavy trucks fueled with a biodiesel blend with those from trucks fueled with petroleum diesel. The biodiesel blend tested is a mixture of 35% biodiesel and 65% petroleum diesel, a blend designated as B35. The study is based on the field test results from West Virginia University's Transportable Heavy Duty Chassis Dynamometer Emissions Testing Laboratory and sponsored by the U.S. Department of Energy. The heavy trucks we tested performed well when the originally equipped compression-ignition engine (diesel engine) was fueled with B35 without any engine modifications. Fuel economy (in terms of gallon per mile) of the two fuels was about the same. The emissions test results have shown that the heavy trucks fueled by B35 emitted sign...
TL;DR: In this article, the authors analyzed >400 particulate samples collected from throughout the Chesapeake Bay region between 1991 and 1998 for polycyclic aromatic hydrocarbons (PAHs).
Abstract: We analyzed >400 particulate samples collected from throughout the Chesapeake Bay region between 1991 and 1998 for polycyclic aromatic hydrocarbons (PAHs). Isomer ratios of PAHs associated with aerosol and surface water particles demonstrate that motor vehicles are a major source of carcinogenic combustion-derived PAHs to Chesapeake Bay. Most of the benz[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene and their isomers in air, rain, and surface waters of Chesapeake Bay appear to be derived from automotive sources. Lesser, but still significant amounts (53(±5)%) of these PAHs in the sea surface microlayer near urban areas are motor vehicle-derived, with 47(±5)% being coal-derived. In contrast, PAHs in surface sediments of Chesapeake Bay are predominantly coal-derived (86(±8)%) and at most 14(±8)% motor vehicle-derived. Thus, carcinogenic PAHs input to the bay from motor vehicles are either degraded prior to deposition to the sediments or are diluted by previously deposited coal-derived PAHs in the seabe...
TL;DR: The occurrence of iodinated X-ray contrast media derived from radiological examinations was investigated in German municipal sewage, sewage treatment plant (STP) effluents, rivers, and groundwater using LC-electrospray tandem MS detection.
Abstract: The occurrence of iodinated X-ray contrast media derived from radiological examinations was investigated in German municipal sewage, sewage treatment plant (STP) effluents, rivers, and groundwater using LC-electrospray tandem MS detection. The four X-ray contrast media, diatrizoate, iopamidol, iopromide, and iomeprol are ubiquitously distributed in the sewage and in the aquatic environment. The X-ray contrast media were not significantly eliminated during the sewage treatment processes close to Frankfurt/Main. On weekdays the loading of the X-ray contrast media was significantly increased, because X-ray examinations are performed in hospitals and radiological practices predominately from Monday to Friday. The maximum concentration measured in STP effluents was 15 μg/L for iopamidol. Due to the high contamination of STP effluents with X-ray contrast media, the respective receiving waters (rivers and creeks) were also highly polluted. Median values up to 0.49 μg/L for iopamidol and 0.23 μg/L for diatrizoate...
TL;DR: The authors describes how economists ascribe values to the things people can choose, and the economic value of an ecosystem function or service relates to the contribution it makes to human welfare, which is the same as the value of a product or service.
Abstract: This paper describes how economists ascribe values to the things people can choose. The economic value of an ecosystem function or service relates to the contribution it makes to human welfare, whe...
TL;DR: In this paper, the effect of indoor particle sources on indoor particle size distributions and concentrations was previously investigated using real-time indoor and outdoor particle size distribution data collected in four homes in Boston in 1996.
Abstract: The effect of indoor particle sources on indoor particle size distributions and concentrations was previously investigated using real-time indoor and outdoor particle size distribution data collected in four homes in Boston in 1996. These data demonstrated the importance of indoor sources (i.e., cooking, cleaning, and movement of people) and air exchange rates on observed indoor concentrations. As part of the continued analyses of these data, a simple physical model was used to determine the source emission and infiltration rates for specific particle sizes. Decay rates were also estimated. Cooking, cleaning, and indoor work (characterized by movement of people) significantly increased PM(0.7-10) concentrations by 0.27, 0.27, and 0.25 μm3 cm-3 min-1, respectively. Cooking was the only variable significantly associated with generation of particles less than 0.5 μm in diameter. Outdoor particles (0.02−0.5 and 0.7−10 μm) were found to contribute significantly to indoor particle levels. Effective penetration ...
TL;DR: In this article, the major and minor constituents of slag from each furnace type and reports the leachability of metals from slag under neutral and acidic conditions were analyzed and the particle size distributions and partitioning coefficients were also reported.
Abstract: Approximately 21 million tons of steel industry slag are produced each year in the United States, and many productive commercial uses of slag have been developed (e.g., road bed, fill material). However, because slag contains heavy metals at concentrations that are higher than in most soil, questions have been raised regarding the need to evaluate the potential human health and environmental hazards associated with current applications. To enhance general understanding of the physical and chemical characteristics of this material, slag samples from 58 active mills with blast furnaces, basic oxygen furnaces, and/or electric arc furnaces were examined. This study profiles the major and minor constituents of slag from each furnace type and reports the leachability of metals from slag under neutral and acidic conditions. Particle size distributions and partitioning coefficients (Kd) are also reported. Although concentrations of metals in slag are elevated relative to concentrations in soil, the metals in slag...
TL;DR: Sulfurospirillum barnesii is capable of anaerobic growth using ferric iron or arsenate as electron acceptors as mentioned in this paper, and it was shown that arsenate reduction was influenced by the method in which arsenate became associated with the mineral phases and may have been strongly coupled with arsenate desorption rates.
Abstract: Sulfurospirillum barnesii is capable of anaerobic growth using ferric iron or arsenate as electron acceptors. Cell suspensions of S. barnesii were able to reduce arsenate to arsenite when the former oxyanion was dissolved in solution, or when it was adsorbed onto the surface of ferrihydrite, a common soil mineral, by a variety of mechanisms (e.g., coprecipitation, presorption). Reduction of Fe(III) in ferrihydrite to soluble Fe(II) also occurred, but dissolution of ferrihydrite was not required in order for adsorbed arsenate reduction to be achieved. This was illustrated by bacterial reduction of arsenate coprecipitated with aluminum hydroxide, a mineral that does not undergo reductive dissolution. The rate of arsenate reduction was influenced by the method in which arsenate became associated with the mineral phases and may have been strongly coupled with arsenate desorption rates. The extent of release of arsenite into solution was governed by adsorption of arsenite onto the ferrihydrite or alumina phase...
TL;DR: In this article, the effects of humic acid adsorption, concentration polarization, and aggregate deposition on the rate and extent of fouling were investigated using a broad range of molecular weight cutoffs.
Abstract: Recent studies have shown that natural organic matter (e.g., humic and fulvic acids) is a major foulant during ultrafiltration of surface water. The objective of this study was to develop a more complete understanding of the mechanisms governing humic acid fouling, including the effects of humic acid adsorption, concentration polarization, and aggregate deposition on the rate and extent of fouling. Data were obtained with Aldrich and Suwannee River humic acids using ultrafiltration membranes with a broad range of molecular weight cutoffs. Fouled membranes were also examined using streaming potential and contact angle measurements. The extent of flux decline was greatest for the largest molecular weight cutoff membranes due to the greater relative hydraulic resistance of the humic acid deposit formed on the surface of these membranes. This humic acid deposit reduced the apparent zeta potential and increased the membrane contact angle. Simple static adsorption and concentration polarization caused relatively little flux decline. Humic acid aggregates had a significant effect on fouling only for the larger molecular weight cutoff membranes. The rate and extent of humic acid fouling increased at low pH, high ionic strength, and in the presence of calcium due to changes in intermolecular electrostatic interactions. These results provide important insights into the mechanisms of humic acid fouling during ultrafiltration.
TL;DR: In this paper, the efficiency of two hyperaccumulating species, four agricultural crop plants, and one woody crop, at phytoextraction of Zn, Cd, and Cu from a polluted calcareous soil was investigated.
Abstract: In a field experiment we investigated the efficiency of two hyperaccumulating species, four agricultural crop plants, and one woody crop, at phytoextraction of Zn, Cd, and Cu from a polluted calcareous soil. In addition, we examined the possibility to enhance the phytoextraction of these metals by application of nitrilotriacetate (NTA) and elemental sulfur (S8) to the soil. Metal uptake by hyperaccumulating species was higher than that by crop species but was generally low in all treatments compared to results reported in the literature, maybe as a result of lower total and available soil metal concentrations. Soil amended with either S8 or NTA increased the solubility (NaNO3-extraction) of Zn, Cd, and Cu ions by factors of 21, 58, and 9, respectively, but plant accumulation of these metals was only increased by a factor of 2−3. As a result, even the highest metal removal rates achieved in this study were still far from what would be required to make this technique practicable for the remediation of the D...
TL;DR: In this paper, the degradation of atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine) by ozone and OH radicals during ozonation and advanced oxidation processes, with the identification of the main degradation products was investigated.
Abstract: The present study investigates the degradation of atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine) by ozone and OH radicals during ozonation and advanced oxidation processes, with the identification of the main degradation products. Besides the dealkylated and amide degradation products(6-amino-2-chloro-4-isopropylamino-s-triazine, 6-amino-2-chloro-4-(ethylamino)-s-triazine, 4-acetamido-2-chloro-6-isopropylamino-s-triazine, 4-acetamido-6-amino-2-chloro-s-triazine, and chlorodiamino-striazine), two new degradation products with an imine group were identified (2-chloro-4-ethylimino-6-isopropylamino-s-triazine and 6-amino-2-chloro-4-ethylimino-s-triazine). The contribution of the different pathways (direct ozone and OH radical reaction) to the overall degradation process has been quantified, and the rate constants of the reactions of atrazine and its main degradation products with both oxidants have been measured. The ethyl group is more reactive than the isopropyl group (i.e. 19 times during ozonation and four times during OH radical attack). The ethyl group reacts in higher proportion through oxidation to acetamide or imine derivates than to dealkylation. In contrast, the isopropyl group reacts mainly through dealkylation to the free amino group. Acetamido and imino groups a re found to be resistant to chemical oxidation. These reactivities were corroborated by the measured values of the rate constants with both oxidants. A combination of product distribution and the kinetic parameters together with ozone and OH radical concentrations allowed us to calculate the evolution of the concentration of the degradation products for a given ozonation process.
TL;DR: In this paper, the organic portion was observed to enhance the water uptake of the (NH4)2SO4-organic aerosol systems by as much as a factor of 2−3 for particles.
Abstract: Deliquescence and hygroscopic growth measurements were performed for four internally mixed aerosol mixtures: NaCl-glutaric acid, NaCl-pinonic acid, (NH4)2SO4-glutaric acid, and (NH4)2SO4-pinonic acid with varying organic mass fractions (0, 0.2, 0.5, 0.8, and 1.0). No effect on the deliquescence relative humidity of the salts was observed for any of the organic mixtures tested. The NaCl-organic mixed aerosols deliquesced at a relative humidity (DRH) 75 ± 1% and the (NH4)2SO4-organic aerosol at 79 ± 1% independent of organic mass fraction. The growth factors at RH = 85 ± 1%, G(85%), were also measured for the different aerosol mixtures. There was an observed decrease in G(85%) with increasing mass fraction of the organic. Measured G(85%) for the mixtures can be approximated as a first step with the assumption that the species absorb water independently. Overall, the organic portion was observed to enhance the water uptake of the (NH4)2SO4-organic aerosol systems by as much as a factor of 2−3 for particles ...