Modeling the competitive effect of phosphate, sulfate, silicate, and tungstate anions on the adsorption of molybdate onto goethite

The mobility of Mo in soils and sediments depends on several factors including soil mineralogy and the presence of other oxyanions that compete with Mo for the adsorbent's retention sites. Batch experiments addressing Mo adsorption onto goethite were conducted with phosphate, sulfate, silicate, and tungstate as competing anions in order to produce competitive two anions adsorption envelopes, as well as competitive two anions adsorption isotherms. Tungstate and phosphate appear to be the strongest competitors of Mo for the adsorption sites of goethite, whereas little competitive effects were observed in the case of silicate and sulfate. Mo adsorption isotherm from a phosphate solution was similar to the one from a tungstate solution. The charge distribution multi-site complexation (CD-MUSIC) model was used to predict competitive adsorption between MoO(4)(2-) and other anions (i.e., phosphate, sulfate, silicate and tungstate) using model parameters obtained from the fitting of single ion adsorption envelopes. CD-MUSIC results strongly agree with the experimental adsorption envelopes of molybdate over the pH range from 3.5 to 10. Furthermore, CD-MUSIC prediction of the molybdate adsorption isotherm show a satisfactory fit of the experimental results. Modeling results suggest that the diprotonated monodentate complexes, FeOW(OH)(5)(-0.5) and FeOMo(OH)(5)(-0.5), were respectively the dominant complexes of adsorbed W and Mo on goethite 110 faces at low pH. The model suggests that Mo and W are retained mainly by the formation of monodentate complexes on the goethite surface. Our results indicate that surface complexation modeling may have applications in predicting competitive adsorption in more complex systems containing multiple competing ions.     

Adsorption characteristics of benzene on biosolid adsorbent and commercial activated carbons

This study selected biosolids from a petrochemical waste-water treatment plant as the raw material. The sludge was immersed in 0.5-5 M of zinc chloride (ZnCl2) solutions and pyrolyzed at different temperatures and times. Results indicated that the 1-M ZnCl2-immersed biosolids pyrolyzed at 500 degrees C for 30 min could be reused and were optimal biosolid adsorbents for benzene adsorption. Pore volume distribution analysis indicated that the mesopore contributed more than the macropore and micropore in the biosolid adsorbent. The benzene adsorption capacity of the biosolid adsorbent was 65 and 55% of the G206 (granular-activated carbon) and BPL (coal-based activated carbon; Calgon, Carbon Corp.) activated carbons, respectively. Data from the adsorption and desorption cycles indicated that the benzene adsorption capacity of the biosolid adsorbent was insignificantly reduced compared with the first-run capacity of the adsorbent; therefore, the biosolid adsorbent could be reused as a commercial adsorbent, although its production cost is high.     

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and dioxin-like polychlorinated biphenyls in rice plants: possible contaminated pathways

Uptake of dioxins was confirmed in rice plants. We determined (i) dioxin concentrations and isomer profiles in leaf+stem samples of rice plants grown in three soils with different dioxin concentrations and isomer profiles and (ii) temporal changes in dioxin concentrations and isomer profiles in rice grown in a paddy field on which agricultural chemicals containing dioxin impurities had been used in previous years. Principal-component and chemical mass-balance analyses of the data showed that dioxin concentrations and isomer profiles in the rice grown in the different soils were similar, even though the dioxin concentrations and isomer profiles of the soils were different. However, the dioxin concentrations in the rice were influenced by dioxin levels in the atmospheric gas phase. Changes in dioxin levels during the growing period of the rice were also strongly influenced by adhesion of the soil to plant components during the early stage of growth, but gradually the influence of the atmospheric gas phase became predominant. Calculated dietary uptake estimates indicated that, even in rice grown in Japan on soil contaminated with high concentrations of dioxins, the amount of dioxins ingested by humans from rice is extremely small, and the amount of dioxins ingested by livestock from forage rice is similar to that for other forage crops.     

Variations of bacterial community structure in flooded paddy soil contaminated with herbicide quinclorac

The denaturing gradient gel electrophoresis (DGGE) method was applied to determine the relative genetic complexity of microbial communities in flooded paddy soil treated with herbicide quinclorac (3,7-dichloro-8-quinoline-carboylic acid). The results obtained showed a significant effect of quinclorac on the development of bacterial populations in soils contaminated with different concentrations of the herbicide at the early time after application. In general, however, the number of populations of the same soil sample treated with the same concentration of the quinclorac differed obviously with increasing incubation time within the early 8 weeks. The scale of differences in banding patterns-showed that the microbial community structures of the quinclorac-treated and non-quinclorac-treated soils were not significantly different after 21 weeks of incubation. Quantification, as demonstrated in this paper, was studied by establishing dose-response relationships. Significant pattern variations were quantified. Prominent DGGE bands were excised, cloned and sequenced to gain insight into the identities of predominant bacterial populations. The majority of DGGE band sequences were related to bacterial genera Clostridium, Sphingobacterium, Xanthomonas and Rhodococcus.     

Probabilistic study of well capture zones distribution at the Lauswiesen field site

The delineation of well capture zones is of utmost environmental and engineering relevance as pumping wells are commonly used both for drinking water supply needs, where protection zones have to be defined, and for investigation and remediation of contaminated aquifers. We analyze the probabilistic nature of well capture zones within the well field located at the "Lauswiesen" experimental site. The test site is part of an alluvial heterogeneous aquifer located in the Neckar river valley, close to the city of Tübingen in South-West Germany. We explore the effect of different conceptual models of the structure of aquifer heterogeneities on the delineation of three-dimensional probabilistic well catchment and time-related capture zones, in the presence of migration of conservative solutes. The aquifer is modeled as a three-dimensional, doubly stochastic composite medium, where distributions of geo-materials and hydraulic properties are uncertain. We study the relative importance of uncertain facies geometry and uncertain hydraulic conductivity and porosity on predictions of catchment and solute time of travel to the pumping well by focusing on cases in which (1) the facies distribution is random, but the hydraulic properties of each material are fixed, and (2) both facies geometry and material properties vary stochastically. The problem is tackled within a conditional numerical Monte Carlo framework. Results are provided in terms of probabilistic demarcations of the three-dimensional well catchment and time-related capture zones. Our findings suggest that the uncertainty associated with the prediction of the location of the outer boundary of well catchment at the "Lauswiesen" site is significantly affected by the conceptual model adopted to incorporate the heterogeneous nature of the aquifer domain in a predictive framework. Taking into account randomness of both lithofacies distribution and materials hydraulic conductivity allows recognizing the existence of preferential flow paths that influence the extent of the well catchment and the solute travel time distribution at the site.     

Culturability and concentration of indoor and outdoor airborne fungi in six single-family homes

In this study, the culturability of indoor and outdoor airborne fungi was determined through long-term sampling (24-h) using a Button Personal Inhalable Aerosol Sampler. The air samples were collected during three seasons in six Cincinnati area homes that were free from moisture damage or visible mold. Cultivation and total microscopic enumeration methods were employed for the sample analysis. The geometric means of indoor and outdoor culturable fungal concentrations were 88 and 102 colony-forming units (CFU) m(-3), respectively, with a geometric mean of the I/O ratio equal to 0.66. Overall, 26 genera of culturable fungi were recovered from the indoor and outdoor samples. For total fungal spores, the indoor and outdoor geometric means were 211 and 605 spores m(-3), respectively, with a geometric mean of I/O ratio equal to 0.32. The identification revealed 37 fungal genera from indoor and outdoor samples based on the total spore analysis. Indoor and outdoor concentrations of culturable and total fungal spores showed significant correlations (r = 0.655, p<0.0001 and r = 0.633, p<0.0001, respectively). The indoor and outdoor median viabilities of fungi were 55% and 25%, respectively, which indicates that indoor environment provides more favorable survival conditions for the aerosolized fungi. Among the seasons, the highest indoor and outdoor culturability of fungi was observed in the fall. Cladosporium had a highest median value of culturability (38% and 33% for indoor and outdoor, respectively) followed by Aspergillus/Penicillium (9% and 2%) among predominant genera of fungi. Increased culturability of fungi inside the homes may have important implications because of the potential increase in the release of allergens from viable spores and pathogenicity of viable fungi on immunocompromised individuals.     

The use of a sequential leaching procedure for assessing the heavy metal leachability in lime waste from the lime kiln at a caustizicing process of a pulp mill

A five-stage sequential leaching procedure was used to fractionate 13 heavy metals (Cd, Cu, Pb, Cr, Zn, Fe, Mn, Al, Ni, Co, As, V, Ba) and sulphur (S) in lime waste from the lime kiln at the causticizing plant of Stora Enso Oyj Veitsiluoto Pulp Mills at Kemi, Northern Finland, into the following fractions: (1) water-soluble fraction (H₂O), (2) exchangeable fraction (CH₃COOH), (3) easily reduced fraction (HONH₃Cl), (4) oxidizable fraction (H₂O₂ + CH₃COONH₄), and (5) residual fraction (HF + HNO₃ + HCl). Although metals were leachable in all fractions, the highest concentrations for most of the metals were observed in the residual fraction (stage 5). It was also notable that the total heavy metal concentrations in lime waste did not exceed the maximal allowable heavy metal concentrations for soil conditioner agents set by the ministry of the Agricultural and Forestry in Finland. The heavy metals concentrations in lime waste were also lower than the maximal allowable heavy metals concentrations of the European Union Directive 86/278/EEC on the protection of environment, and in particular of the soil, when sewage sludge is used in agriculture. The Ca concentration (420 g kg⁻¹; d.w.) was about 262 times higher than the typical value of 1.6 g kg⁻¹ (d.w.) in arable land in Central Finland. However, the concentration Mg (0.2 g kg⁻¹; d.w.) in lime waste was equal to the Mg concentration in arable land in the Central Finland. The lime waste has strongly alkaline pH (12.8) and a neutralizing value (i.e. liming effect) of 47.9% expressed as Ca equivalents (d.w.). This indicates lime waste to be a potential soil conditioner and improvement as well as a pH buffer.     

Quantitation of Hydroxyl Radicals from Photolysis of Fe(III)-Citrate Complexes in Aerobic Water (5 pp)

Background For their high photoreactivity, Fe(III)-carboxylate complexes are important sources of H2O2 for some atmospheric and surface waters. Citrate is one kind of carboxylate, which can form complexes with Fe(III). In our previous study, we have applied Fe(III)-citrate complexes to degrade and decolorize dyes in aqueous solutions both under UV light and sunlight. Results have shown that carboxylic acids can promote the photodegradation efficiency. It is indicated that the photolysis of Fe(III)-citrate complexes may cause the formation of some reactive species (e. g. H2O2 and ·OH). This work is attempted to quantify hydroxyl radicals generated in the aqueous solution containing Fe(III)-citrate complexes and to interpret the photoreactivity of Fe(III)-citrate complexes for degrading organic compounds. Methods By using benzene as the scavenger to produce phenol, the photogeneration of ·OH in the aqueous solution containing Fe (III)-citrate complexes was determined by HPLC. Results and Discussion In the aqueous solution containing 60.0/30.0 mM Fe(III)/citrate and 7.0 mM benzene at pH 3.0, 96.66 mM ·OH was produced after irradiation by a 250W metal halide light (l ≥ 313 nm) for 160 minutes. Effects of initial pH value and concentrations of Fe(III) and citrate on ·OH radical generation were all examined. The results show that the greatest photoproduction of ·OH in the aqueous solution (pH ranged from 3.0 to 7.0) was at pH 3.0. The photoproduction of ·OH increased with increasing Fe(III) or citrate concentrations. Conclusion In the aqueous solutions containing Fe(III)-citrate complexes, ·OH radicals were produced after irradiation by a 250W metal halide light. It can be concluded that Fe(III)-citrate complexes are important sources of ·OH radicals for some atmospheric and surface waters. Recommendations and Outlook It is believed that the photolysis of Fe(III)-citrate complexes in the presence of oxygen play an important role in producing ·OH both in atmospheric waters and surface water where high concentrations of ferric ions and citrate ions exist. The photoproduction of ·OH has a high oxidizing potential for the degradation of a wide variety of natural and anthropogenic organic and inorganic substances. We can use this method for toxic organic pollutants such as organic dyes and pesticides.     

HCHs and DDTs in sediment-dwelling animals from the Yangtze Estuary, China

HCHs and DDTs in sediment-dwelling animals including mollusks and crabs from the Yangtze Estuary were determined by GC-ECD. Levels of t-HCH were in the range of 1.2-5.5 ng g(-1) and averaged 3.5 ng g(-1) in mollusks, while t-DDT concentrations ranged from 26.0 to 68.8 ng g(-1), with a mean of 34.5 ng g(-1). In crabs t-HCH concentrations varied from 2.0 to 25.7 ng g(-1) and averaged 13.8 ng g(-1), whereas the concentrations of t-DDT were in the range of 1.5-24.8 ng g(-1) with a mean value of 5.9 ng g(-1). The HCHs and DDTs levels depend on geographical position and sources, showing the high levels at fresh water area in the estuary, such as XP, CM and LHK sites, and lower at brackish water area, such as FX site, and little difference between species. Results also indicate there was no significant relationship between t-HCH (t-DDT) concentrations and lipid contents both in mollusks and crabs because of non-equilibrium state under a specific estuarine dynamics; smaller individuals accumulated more HCHs and DDTs than larger individuals of mollusks at LHK site, showing different uptake rate for these pesticides; moreover, HCHs and DDTs levels were lower in female crab bodies than male crab bodies suggesting that the release of spawning. BSAFs (Biota- Sediment Accumulation Factors) from sediment-dwelling animals for HCHs and DDTs show a significant "one high with two low" and "one low with two high" effect in the Yangtze Estuary.     

Treatment of log yard run-off by irrigation of grass and willows

Log yard run-off is a potential environmental risk, among other things because it creates an oxygen deficiency in receiving watercourses. This study was conducted to investigate the purification efficiency of soil-plant systems with couchgrass (Elymus repens) and willows (Salix sp.) when intensively irrigated with run-off from an open sprinkling system at a Norway spruce (Picea abies) log yard. The purification efficiency was determined both at the field scale (couchgrass) and in 68-L lysimeters (couchgrass and willows). Groundwater in the field and drainage water from the lysimeters were analysed for Total Organic Carbon (TOC), distillable phenols, total P, and total N. Retention of TOC, phenols and P occurred but no difference between couchgrass and willows was observed. The system had better purification capacity at the field scale than in the lysimeters.