Showing papers in "Environmental Science & Technology in 1995"

Phytoextraction: The Use of Plants To Remove Heavy Metals from Soils

Abstract: A small number of wild plants which grow on metal contaminated soil accumulate large amounts of heavy metals in their roots and shoots This property may be exploited for soil reclamation if an easily cultivated, high biomass crop plant able to accumulate heavy metals is identified Therefore, the ability of various crop plants to accumulate Pb in shoots and roots was compared While all crop Brassicas tested accumulated Pb, some cultivars of Brassica juncea (L) Czern showed a strong ability to accumulate Pb in roots and to transport Pb to the shoots (1083 mg Pb/g DW in the roots and 345 mg Pb/g DW in the shoots) B juncea was also able to concentrate Cr{sup -6}, Cd, Ni, Zn, and Cu in the shoots 58, 52, 31, 17, and 7 fold, respectively, from a substrate containing sulfates and phosphates as fertilizers The high metal accumulation by some cultivars of B juncea suggests that these plants may be used to clean up toxic metal-contaminated sites in a process termed phytoextraction

Effect of aging of chemicals in soil on their biodegradability and extractability.

Abstract: A study was conducted to determine whether the time that a compound remains in a soil affects its biodegradability and the ease of its extraction. Phenanthrene and 4-nitrophenol were aged in sterilized loam and muck, and bacteria able to degrade the compounds were then added to the soils. increasingly smaller amounts of phenanthrene in the muck and 4-nitrophenol in both soils were mineralized with increasing duration of aging. Aging also increased the resistance of phenanthrene to biodegradation in nutrient-amended aquifer sand. The rate of miner- alization of the two compounds in both soils declined with increasing periods of aging. The amount of phenanthrene and 4-nitrophenol added to sterile soils that was recovered by butanol extraction declined with duration of aging, but subsequent Soxhlet extraction recovered phenanthrene from the loam but not the muck. The extents of mineralization of phenanthrene previously incubated for up to 27 days with soluble or insoluble organic matter from the muck were similar. Less aged than freshly added phenanthrene was biodegraded if aggregates in the muck were sonically disrupted. The data show that phenanthrene and 4-nitrophenol added to soil become increasingly more resistant with time to biodegradation and extraction.

Rhizofiltration: The Use of Plants to Remove Heavy Metals from Aqueous Streams

Abstract: Heavy metal pollution of water is a major environmental problem facing the modern world. Rhizofiltration - the use of plant roots to remove heavy metals from water is an emerging environmental clean-up technology. Roots of many hydroponically grown terrestrial plants e.g. Indian mustard, sunflower (Hefianthus annuus L.) and various grasses effectively removed toxic metals such as CU{sup -2}, Cd{sup +2}Cr{sup +6}, Ni{sup +2}Pb{sup +2} and Zn{sup +2} from aqueous solutions. Roots of B. juncea concentrated these metals 131 to 563-fold (on a DW basis) above initial solution concentrations. Pb removal was based on tissue absorption and on root-mediated Pb precipitation in the form of insoluble inorganic compounds, mainly Pb phosphate. At high Pb concentrations precipitation played a progressively more important role in Pb removal than tissue absorption, which saturated at approximately 100 {mu}g Pb/g DW root. Dried roots were much less effective than live roots in accumulating Pb and in removing Pb from the solution.

How toxic are toxic chemicals in soil

Abstract: Assessments of the hazard of toxic chemicals in soil are made without concern about the possibility that their bioavailability may change with time. The patterns of disappearance of persistent compounds in the field and laboratory studies show a declining availability to microorganisms with residence time in soil. Changes in extractability with residence time and the kinetics of sorption and desorption suggest that the compounds are becoming sequestered in inaccessible microsites within the soil matrix. Diminishing toxicity as chemicals age in soil is evident in a limited number of assessments. Such findings suggest that the hazard and risk from toxic chemicals diminish as the compounds persist in soil.

Metal Ion Binding to Humic Substances: Application of the Non-Ideal Competitive Adsorption Model

Abstract: The application of a new model to describe metal ion binding by humic acids is discussed. Metal ion binding is always of a competitive nature since the proton is always present. Although of great practical importance, the combination of a chemically heterogeneous system with competitive binding poses difficult problems from both experimental and theoretical points of view. The new Non-Ideal Competitive Adsorption model (NICA model) used here is able to account for the non-ideal binding to heterogeneous ligands. A good description of the binding of H, Ca, Cd, and Cu to a purified peat humic acid is achieved over a wide range of free metal ion concentrations (-2 > log Me 2+ > -14) and pH (2 < pH < 10). The results show that binding of metal ions to humic acid is strongly influenced by the intrinsic chemical heterogeneity of the humic material itself as well as by ion-specific non-ideality. The results indicate that copper competes much more efficiently with protons bound to the phenolic type groups than calcium and cadmium.

TiO2 Photocatalysis for Indoor Air Applications: Effects of Humidity and Trace Contaminant Levels on the Oxidation Rates of Formaldehyde, Toluene, and 1,3-Butadiene

Abstract: Persistent indoor air contaminants, those originating from emissions by interior furnishings, occupants, and materials of construction, typically exist in concentrations below 100 parts per billion (ppb) on an individual basis. The total of distinct contaminants may number in the hundreds with an equivalent accumulated concentration of one part per million. This study investigated the effects of humidity and trace (sub-ppmv) contaminant levels on the oxidation rates of formaldehyde, toluene, and 1,3-butadiene. The evaluation also included variations in UV intensity and flow residence time. UV intensities from inexpensive mercury fluorescent lamps, those which are expected to be employed in a practical photocatalytic purifier, are in the mW/cm 2 range. For this reason, the study included UV intensities in that range. The reactor element used in the study was a low pressure drop alumina reticulate, wash-coated with Degussa P25 titania. The data indicated that the reaction was first-order for the three reactants at the subppmv level. An important finding was that competitive adsorption between water and trace (sub-ppmv) contaminants has a significant effect on the oxidation rate. The dependencies of humidity and contaminant concentrations on the oxidation rates are explained as being the results of competitive adsorption on available hydroxyl adsorption sites and of changes in hydroxyl radical population levels

Organic pollutant accumulation in vegetation.

Abstract: Recent advances in the study of organic pollutant accumulation in vegetation are reviewed. Major areas include (a) the mechanism of uptake by vegetation, (b) the use of vegetation to indicate contamination levels, and (c) the importance of vegetation as a pollutant sink. The mechanism of vegetation uptake of organic pollutants is governed by the chemical and physical properties of the pollutant, environmental conditions, and the plant species. We recommend that additional field studies be done on the uptake of industrial pollutants by native plants and that empirical models and controlled exposure experiments be validated under field conditions. Vegetation can be used to qualitatively indicate organic pollutant atmospheric contamination levels as long as the mechanism of accumulation is considered. Vegetation has been used to identify point sources of pollutants and to determine regional and global contamination patterns. Plant pollutant concentrations should be normalized to the plant lipid concentration or surface area, especially when directly comparing different species. Although vegetation has a great potential to accumulate organic pollutants, little is known about the quantitative importance of vegetation as a pollutant sink. Overall recommendations for future research are presented.

Enhanced Rates of Photocatalytic Degradation of an Azo Dye Using SnO2/TiO2 Coupled Semiconductor Thin Films.

Abstract: We present here for the first time the results from electrochemically assisted photocatalytic experiments using coupled TiO{sub 2}/SnO{sub 2} semiconductor thin films in the degradation of textile dye effluent. We show that by using such a system the oxidative efficiency of photocatalytic semiconductor systems in degrading a commercial azo dye such as Acid Orange 7 (AO7) can be improved. The results presented here on the decolorization of the azo dye AO7 represents a major step forward in the development of new advanced oxidation processes for the treatment of such industrial waste. The improved charge separation as a result of coupling two semiconductor systems with different energy levels and the applied anodic bias is responsible for the enhancement in the rate of photocatalytic degradation. 20 refs., 6 figs.

Lead immobilization from aqueous solutions and contaminated soils using phosphate rocks.

Abstract: This research investigated the effectiveness of phosphate rocks in immobilizing Pb from aqueous solutions and contaminated soils. Different amounts of phosphate rocks were reacted with aqueous solutions containing Pb or with Pb-contaminated soils. The results show that phosphate rocks were effective in immobilizing Pb from aqueous solutions with a minimum Pb removal of 38.8-100%. The reaction time had less effect on Pb immobilization than the quantity of phosphate rocks used. Selected phosphate rocks reduced water-soluble Pb from a contaminated soil by 56.8-100%. The primary mechanism of Pb immobilization was via dissolution of phosphate rocks and precipitation of a fluoropyromorphite-like mineral. Different methods of mixing phosphate rocks and soil and incubation time had little effect on Pb immobilization. Our results strongly demonstrate that phosphate rocks may provide a cost-effective way to remediate Pb-contaminated water, soils, and wastes.

Transformation kinetics of phenols in water: photosensitization by dissolved natural organic material and aromatic ketones.

Abstract: Different dissolved natural organic materials photosensitize the transformation of a series of methyl and methoxy phenols at pH 8 with a very similar high selectivity (reactivity range 50). This selectivity falls in the range of that achieved using the aromatic ketones benzophenone (BP), 3'-methoxyacetophenone (3'-MAP), and 2-acetonaphthone (2-AN) as model photosensitizers. For both natural and model sensitizers, the photooxidation at pH 8 is not controlled by singlet oxygen. Deuterium isotope effects (k H /k D ) of different phenols are 0.7-1.3 for humic and fulvic acids and 1.1-1.7 for BP, suggesting an electron transfer mechanism. In contrast, the isotope effect for 2-AN of 4 indicates an H-atom abstraction reaction. The results show that reactive excited triplet states are important photooxidants in natural waters and should be considered for assessing the abiotic degradation of chemicals. The reactive triplet state concentration is estimated to be 10 -14 M in the top meter of Lake Greifensee under summer noon sunlight, and this leads to a half-life of 7 h for 2,4,6-trimethylphenol. Further still uncharacterized photooxidants derived from the dissolved organic material are also involved in the phototransformation of the phenols.

Reduction of Substituted Nitrobenzenes by Fe(II) in Aqueous Mineral Suspensions.

Abstract: The kinetics of the reduction of 10 monosubstituted nitrobenzenes (NBs) by Fe(II) has been investigated under various experimental conditions in aqueous suspensions of minerals commonly present in soils and sediments. Aqueous solutions of Fe(II) were unreactive. In suspensions of Fe(III)-containing minerals (magnetite, goethite, and lepidocrocite), Fe(II) readily reduced the NBs to the corresponding anilines in a strongly pH-dependent reaction. Our results suggest that on other mineral surfaces (γ-aluminum oxide, amorphous silica, titanium dioxide, and kaolinite) iron (hydr)oxide coatings are indispensable to promote the reduction of NBs by adsorbed Fe(ll). Apparent pseudo-first-order rate constants, k obs , were used to describe the initial kinetics of the NB reduction, covering several half-lives of the compounds. The distinct effect of substituents on k obs and the observed pronounced competition between different NBs indicate that precursor complex formation as well as the (re)generation of reactive surface sites are rate-determining steps in the overall reduction of the NBs. The results of this study demonstrate that Fe(ll) adsorbed on iron (hydr)oxide surfaces or surface coatings may play an important role in the reductive transformation of organic pollutants in subsurface environments. Our findings may also contribute to a better understanding of the various redox processes involved in groundwater remediation techniques based on Fe(0) as the bulk reductant.

Coupled Iron Corrosion and Chromate Reduction: Mechanisms for Subsurface Remediation

Abstract: The reduction of chromium from the Cr(VI) to the Cr(III) state by the presence of elemental, or zero-oxidation-state, iron metal was studied to evaluate the feasibility of such a process for subsurface chromate remediation. Reactions were studied in systems of natural aquifer materials with varying geochemistry. Different forms of iron metal had significantly different abilities to reduce chromate, ranging from extremely rapid to essentially no effect. Impure, partially oxidized iron was most effective, with iron quantity being the most important rate factor, followed by aquifer material type and solid :solution ratio. Evidence for chromium-iron hydroxide solid solution (Cr x, Fe 1-x )(OH) 3 (ss) formation was obtained by electron probe microanalysis. A cyclic, multiple reaction electrochemical corrosion mechanism, enhanced by the development of an electrical double-layer analogue, is proposed to explain the differing iron reactivities and aquifer material effects.

Characterization of aquatic colloids and macromolecules. 1. Structure and behavior of colloidal material

Abstract: Parts 1 and 2 of this series are tutorial feature articles exceptionally published as Critical Reviews for editorial reasons. They intend to give to the nonspecialist an overview of the major aspects of the characterization of aquatic colloids in perspective of their properties. For this reason, there is a close link between parts 1 and 2, which in reality form one single paper. In these papers, the words colloids and macromolecules refer to any organic or inorganic entity in the size range of 1 nm to 1 μm. In aquatic systems, they form inherently unstable suspensions due to their propensity to undergo conformational changes, aggregate, and then sediment. These factors should be considered carefully in the development of any procedure for the characterization of colloidal material. In this context, part 1 of this series describes the chemical composition and morphology of aquatic colloids and their aggregates, their size distribution, and the main factors that influence the aggregate structure and formation kinetics. Emphasis is placed on structure-behavior relationships of the colloidal material of surface waters. Part 2 discusses some commonly used characterization procedures on the basis of the above properties.

Development of a Gold Amalgam Voltammetric Microelectrode for the Determination of Dissolved Fe, Mn, O2, and S(-II) in Porewaters of Marine and Freshwater Sediments.

Abstract: A solid-state voltammetric gold amalgam microelectrode has been developed for the measurement of dissolved O 2 , S(-II), Fe, and Mn in the porewaters of marine sediments. This electrode can provide more information at (sub)millimeter depth resolution on all of the major redox species found in the environment than membrane microelectrodes which usually can measure only one of these species per electrode. We describe the construction, standardization, analytical validation, and application of a microelectrode to marine sediments. The use of the microelectrode takes advantage of the fast scan voltammetric methods for simultaneous measurement of all redox species during one potential scan. Electrochemical conditioning of the solid-state microelectrode between voltage scans while deployed in waters and sediments allows for repeated use of the electrode. Finally, we demonstrate depth profiles at millimeter resolution for the redox species in a Delaware salt marsh. The profiles observed are consistent with the known biogeochemical cycling of the target redox species. In addition, we provide evidence for H 2 O 2 , iron(II) sulfide complexes, and iron(III) colloids or organic complexes in porewaters.

Using input-output analysis to estimate economy-wide discharges

Abstract: Life-cycle assessment models attempt to quantify the environmental implications of alternative products and processes, tracing pollution discharges and resources use through the chain of producers and consumers. Present life-cycle assessments must draw boundaries that limit consideration to a few producers in the chain from raw materials to a finished product. We show that this limitation considers only a fraction of the environmental discharges associated with a product or process, thereby making current assessments unreliable. We propose an approach that uses economic input-output analysis and pollution discharge data and apply the model to automobiles, refrigerators, and computer purchases, and to a comparison of paper and plastic cups.

Influences of Watershed Characteristics on Mercury Levels in Wisconsin Rivers

Abstract: Total and monomethyl mercury were measured at 39 river sites in Wisconsin during fall 1992 and spring 1993. Using a Geographic Information System (GIS), we delineated watersheds with unique and homogeneous physical characteristics. Mean unfiltered total Hg (Hg T ) was higher in spring (7.94 ng L -1 ) than in fall (3.45 ng L -1 ). Major differences in Hg T yields were observed among various land-use groupings. In wetland/forest watersheds, elevated Hg T fluxes were associated with the filtered phase, while in agricultural watersheds, increased Hg T fluxes were due to particle loading. Monomethylmercury (MeHg) yields from wetland/forest sites were higher than agricultural/forest sites and agricultural only sites. Percent wetland surface area was positively correlated with MeHg yield. These results identify the importance of land use and land cover in influencing Hg concentrations, speciaton, and transport in rivers.

Subjective judgments by climate experts.

Abstract: Structured interviews using `expert elicitation` methods drawn from decision analysis were conducted with 16 leading U.S. climate scientists. We obtained quantitative, probabilistic judgments about a number of key climate variables and about the nature of the climate system. We also obtained judgments about the relative contributions of various factors to the uncertainty in climate sensitivity. We found strong support for the importance of convection/water vapor feedback and of cloud optical properties. A variety of questions were posed to elicit judgments about future research needs and the possible sources and magnitude of future surprises. The results reveal a rich diversity of expert opinion and, aside from climate sensitivity, a greater degree of disagreement than is often conveyed in scientific consensus documents. Research can make valuable contributions, but we interpret our results to mean that overall uncertainty about the geophysics of climate change is not likely to be reduced dramatically in the next few decades. 22 refs., 5 figs., 2 tabs.

Occurrence and distribution of pharmaceutical organic compounds in the groundwater downgradient of a landfill (grindsted, denmark).

Abstract: Introduction Usually landfill leachates contain specific organic compounds as BTEXs (benzene, toluene, ethylbenzene, and xylenes), chlorinated aliphatic hydrocarbons and chlorobenzenes originating from household chemicals and waste from small businesses (I). However, where industrial waste has been landfilled, the leachate may contain many other organic compounds (2). Another paper of ours (3) described the distribution of commonly found organic compounds in the leachate plume downgradient of the Grindsted Landfill and discussed the fate of the organic compounds in view of the redox environments determined in the plume (4) . In this paper, we describe the occurrence and distribution of organic compounds originating from waste from the pharmaceutical industry in the groundwater downgradient of the same landfill. According to our knowledge, this is the first report on pharmaceutical compounds in a leachate plume.

Reduction of Cr(VI) in the Presence of Excess Soil Fulvic Acid.

Abstract: The rate of hexavalent chromium reduction by a soil fulvic acid (SFA) was measured in aqueous solutions where concentrations of Cr(VI), H + , and SFA were independently varied Rates of reduction increase strongly with decreasing pH Typical Cr(VI)-SFA reactions display a nonlinear reduction of Cr(VI) with timethat cannotadequately be modeled by either firstorder or second-order rate equations An empirical rate equation that treats the SFA as a continuum of reactive groups which reduce Cr(VI) at varying rates adequately describes the effects of solution parameters on the rates of Cr(VI) reduction The rate equation is R=k r [HCrO 4 - ][SFA][Cr(VI)] 0 P[H + ] q where [Cr(VI)] 0 is the initial Cr(VI) concentration

Degradation of Atrazine by Fenton's Reagent: Condition Optimization and Product Quantification.

Abstract: Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] degradation by Fenton's reagent (FR) was determined as a function of reagents' concentration and ratios and pH in batch treatments. The optimal mixture, 2.69 mM (1 :1) FeSO 4 :H 2 O 2 , completely degraded [2,4,6- 14 C]atrazine (140 μM) in ≤30 s primarily to 2-chloro-4,6-diamino-6-triazine (CAAT, 23%) and 2-acetamido-4-amino-6-chloro-s-triazine (CDAT, 28%). Chloride release of 55 ± 9% indicated that dehalogenated s-triazines accounted for the balance of 14 C. Higher FR concentrations lowered CDAT concentrations, but CAAT and the dehalogenated s-triazines persisted. Atrazine degradation decreased from 99% at pH 3 to 37% at pH 9. Thus, FR can rapidly degrade atrazine, but post-treatments may be necessary to eliminate residual chloro-s-triazines like CDAT and CAAT.

Normalization and elemental sediment contamination in the coastal United States.

Abstract: Elemental contamination has been examined in sediments collected from 350 sites along the coast of the United States by NOAA's National Status and Trends (NS&T) Program. To isolate natural from man-made factors, data from 60 sites with fewer than 10 000 people living within 20 km were used to test correlations between concentrations of trace elements and four candidate normalizing factors : iron, aluminum, grain size, and total organic carbon. At least 50% of the concentration variations for the elements As, Cr, Cu, Ni, Pb, Sn, and Zn can be accounted for by covariation with Fe or Al, and either of those major elements can be used for normalization. For Ag, Cd, Hg, Sb, and Se, on the other hand, no candidate normalizers accounted for more than even 30% of the variation. Based on these results, the spatial extent of contamination has been examined, and it was found that severe contamination is mostly limited to small areas near large population centers.

Reactions at Oxide Surfaces. 1. Oxidation of As(III) by Synthetic Birnessite.

Abstract: The rates and mechanisms of the reactions between aqueous As(III) and synthetic birnessite (δ-MnO_2) particles were studied. The experimental results at pH 4 indicate that the depletion of As(III) from solution is rapid, with a time scale of minutes. The oxidation product As(V) is released almost as quickly, while the release of the reduction product Mn(II) is slightly slower. The results also show that the concentration of dissolved oxygen has no effect on the rate of reaction. These observations suggestthat (i) birnessite directly oxidizes As(III) through a surface mechanism, (ii) the adsorption of As(III) is the slowest step in the production of As(V), and (iii) the reaction products As- (V) and Mn(II) are released via different mechanisms. The time-dependent behavior of the aqueous reactants and products over a pH range from 4 to 8.2, and a temperature range from 15 to 35 °C is also discussed. The rates of As(III) oxidation by inorganic redox reactions with manganese dioxides are compared to observed As(III) oxidation rates in natural aquatic systems.

Rates and Mechanism of Fe(II) Oxidation at Nanomolar Total Iron Concentrations.

Abstract: A fully automated luminol-based chemiluminescence system has been developed for rapid analysis of Fe(II) at natural levels. Using this system, the rates of Fe(ll) oxidation in 0.7 M NaCI have been measured for nanomolar concentrations of Fe(ll) over the pH range 7.0-8.3. When the production and decomposition of H 2 O 2 in the system were considered, measured rates at these levels were in excellent agreement with a model based on previously reported rate constants determined using micromolar levels of Fe(II). These results show that O 2 - and OH. intermediates produced as a result of Fe(ll) oxidation remain effective as Fe(ll) oxidants in these controlled conditions. The chemical model for Fe(ll) oxidation also allows prediction of steady-state H 2 O 2 and O 2 - concentrations that result from the oxidation of micromolar levels of Fe(ll). The concentration of both species increases exponentially with increasing pH. At pH 8.2, the predicted H 2 O 2 and O 2 - concentrations are 220 and 2.3 nM, respectively. The predicted H 2 O 2 concentrations are in excellent agreement with laboratory measurements. These results suggest that significant concentrations of H 2 O 2 and O 2 - should be present at the oxic-anoxic interface of marine environments where micromolar levels of Fe(ll) are in contact with dissolved oxygen.

Modeling of the Proton-Metal Ion Exchange in Biosorption

Abstract: Biosorption of the heavy metal ions Cd 2+ , Cu 2+ , and Zn 2+ by previously protonated nonliving biomass of the marine alga Sargassum fluitans was observed to be coupled with a release of protons. Metal ion binding experiments with continuously controlled pH were performed. The metal ion and proton binding at equilibrium were modeled as a function of pH and metal ion concentration using a modified multicomponent Langmuir sorption model. Both the exchange of metal ions for protons from functional groups in their acidic form and the sorption of metal ions on ionized groups were considered. The model is applicable to adsorption by biomass with free or protonated metal binding sites as well as to metal ion desorption with acids since the direction of the reaction depends simply on the given initial conditions. The model parameters were incorporated into the MINEQL+ equilibrium program, leading to a prediction of the equilibrium, e.g., of metal ion laden biosorbent desorption performance for given initial conditions.

Mechanisms of Formation and Destruction of Polychlorinated Dibenzo=p=dioxins and Dibenzofurans in Heterogeneous Systems

Abstract: Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans are toxic compounds formed during natural processes and human activities. The basic questions about PCDD/F formation such as (1) what is the influence of process parameters on the formation process, (2) what reaction mechanisms are involved in formation, and (3) what kinetics describes PCDD/F formation are discussed, and recommendations are given.

Anaerobic corrosion of granular iron: measurement and interpretation of hydrogen evolution rates.

Abstract: Anaerobic corrosion of iron metal produces Fe 2+ , OH - , and H 2 (g). Growing interest in the use of granular iron in groundwater remediation demands accurate corrosion rates to assess impacts on groundwater chemical composition. In this study, corrosion rates are measured by monitoring the hydrogen pressure increase in sealed cells containing iron granules and water. The principal interference is hydrogen entry and entrapment by the iron. The entry rate is described by Sievert's low (R = kP H2 0.5 ), and the rate constant, k, is evaluated by reducing the cell pressure once during a test. For the 10-32 mesh iron used in this study, k initially was 0.015 but decreased to 0.009 mmol kg -1 d -1 kPa -0.5 in 150 d. The corrosion rate in a saline groundwater was 0.7 ± 0.05 mmol of Fe kg -1 d -1 at 25 °C-identical under water-saturated or fully-drained conditions. The rate decreased by 50% in 150 d due to alteration product buildup. The first 40-200 h of a corrosion test are characterized by progressively increasing rates of pressure increase. The time before steady-state rates develop depends on the solution composition. Data from this period should be discarded in calculating corrosion rates. Tests on pure sodium salt solutions at identical equivalent concentrations (0.02 equiv/L) show the following anion effect on corrosion rate : HCO 3 > SO 4 2- > Cl - . For NaCl solutions, corrosion rates decrease from 0.02 to 3.0 m.

Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in air at an urban and a rural site near Lake Michigan

Abstract: Air samples were collected at an urban (Chicago, IL) and a rural (University of Wisconsin at Green Bay, UWGB) site during February 1988 to determine concentrations and particle/gas distributions of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Geometric mean ΣPAHs of molecular weights ≥166 were 195 ng/m 3 in Chicago and 14 ng/m 3 at UWGB. Ratios among PAHs suggested that some labile compounds were depleted during atmospheric transport. Geometric mean ΣPCBs (45 congeners) were 1.3 ng/m 3 in Chicago and 0.13 ng/m 3 at UWGB. PCB profiles of most samples in Chicago and all at UWGB were skewed toward the lower molecular weight congeners, as in mixtures of Aroclors 1242 and 1254. Two Chicago samples showed a heavy PCB profile similar to Aroclor 1260. Apparent particle/gas partition coefficients (K p ) were well correlated with liquid-phase vapor pressures (po L ) within a class of compounds (PAHs or PCBs). PAHs were sorbed to a greater degree than PCBs for compounds of the same volatility. Slopes of log K p vs log p o L plots deviated from the expected value of -1 in Chicago, suggesting nonequilibrium effects. Aerosols at UWGB appeared to be closer to equilibrium with the gas phase, as indicated by slopes close to -1. Measured particulate percentages in the two locations were within a factor of 2 of those predicted by the Junge-Pankow adsorption model.

Comprehensive Approach toward Understanding Element Speciation and Leaching Behavior in Municipal Solid Waste Incineration Electrostatic Precipitator Ash.

Abstract: A comprehensive approach was used to characterize speciation and leaching behavior of major, minor, and trace elements in electrostatic precipitator (ESP) ash from a Canadian MSW incinerator. Neutron activation analysis (NAA), X-ray powder diffraction (XRPD), scanning electron microscopy/X-ray microanalysis (SEM/XRM), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS) were used to quantify elements, describe particles and phase associations, identify bulk and surface mineral phases, and identify the speciation of elements. SEM/XRM showed a complex polycrystalline material covering aluminosilicate spheres. XPS, as a surface technique, provided information on speciation at the particle surface where leaching first occurs. SIMS showed molecular fragments indicative of speciation and enrichment of volatile species (K, Zn, Cl, S, Pb) in the fine polycrystalline material. Many of these phases readily dissolve during leaching. Dissolution behavior and pH-dependent leaching could be modeled with the geochemical thermodynamic equilibrium model MINTEQA2. The abilityto model leaching behavior provides an opportunity to examine possible disposal or treatment behavior.