Partitioning Of Pollutants Research Articles

Modeling of the sorption and diffusion processes of volatile organic air pollutants in grape fruits.

A mathematical model for the description of the sorption and diffusion processes of gaseous toluene and p-xylene in fruits of grape has been proposed. This model is based on the Fick's II low regarding a particle with a spherical shape (such as the berry of grapevine) and describes changes of air pollutant concentrations in different layers of the fruit, that is, the wax, peel, and pulp, during an exposure to contaminated air. The mass transfer coefficient and diffusion coefficients in the respective layers can be estimated using the experimental values. The theoretical data and the results from the exposure under steady-state laboratory conditions were compared and showed a good applicability of the proposed model for the prediction of volatile air pollutant partitioning in grape berries.

Conformations and aggregate structures of sorbed natural organic matter on muscovite and hematite

In-solution atomic-force microscopy was used to characterize molecular dimensions and aggregate structures of natural organic matter (NOM) sorbed to the basal-plane surfaces of muscovite and hematite as a function of pH (3–11), ionic strength (0.001–0.3 M), NOM concentration (20–100 mgC L −1), and cation electrolyte identity (Ca, Na, Li added as Cl-salts). Electrolyte identity and concentration exerted important effects on image stability, particle size, and sorption density. On mica, the presence of either Ca 2+ or Li + led to more stable images than Na +. For example, at pH 3, we were unable to obtain stable images of NOM on mica in NaCl. However, at pH 3 in CaCl 2 and LiCl solutions, we observed adsorbed spheres with diameters appropriate for single molecules. A higher apparent adsorption density was observed in CaCl 2 than in LiCl, consistent with previous reports that Ca enhances NOM adsorption. In LiCl, the spheres often were aggregated into small groups whereas in CaCl 2, they were mostly isolated. At intermediate pH and relatively low NOM concentrations on mica, larger spherical aggregates were observed, but at higher NOM concentrations, we observed ring structures with nanoporosity that could be important for partitioning of organic pollutants. At high pH on mica, we observed an highly ordered array which most probably indicates reordering of the mica surface structure as Si released by dissolution interacts with NOM. This indicates that NOM may play an important role in phyllosilicate diagenesis. On hematite at pH 4 and in the presence of high dissolved iron concentration, large spherical NOM aggregates were observed, consistent with observations by Myneni et al. (1999) using in solution X-ray imaging. Overall our results demonstrate that NOM sorbs in complex structures and aggregates. Therefore, current models of NOM sorption are likely overly simplistic and require further direct verification.

Impact of frontal systems on estuarine sediment and pollutant dynamics

In this paper, a brief description of frontal systems, their modes of occurrence and impact on the estuarine environment, is presented. Previous studies of estuarine fronts have largely focused on the water surface and within the water column. New observations in the Tay Estuary, Scotland have shown that the presence of fronts within the water column may be marked, not only by surface foam bands, but also by abrupt (i.e. non-gradational) changes in the underlying bedform morphology and/or sediment facies, as detected using side-scan sonar. This preliminary evidence suggests that fronts may exert a control, not only on the surface and intra-water column sediment and pollutant partitioning, but also on the distribution and persistence of bedload transport pathways.

Phase partition of organic pollutants between coal tar and water under variable experimental conditions

On some abandoned manufactured-gas plant sites the presence of a particular non-aqueous phase liquid (NAPL), namely coal tar, represents a potential source of groundwater pollution. The aim of this study was to characterise the phase partition of aromatic pollutants between coal tar and water. Batch trials have been carried out in order to evaluate the state of phase partition equilibrium of pollutants between coal tar and water, under variable experimental conditions (temperature, pH, ionic strength, coal tar composition). The experimental results clearly show that coal tar cannot be considered as an ideal solution with regards to phase partition of pollutants with water. The main identified mechanisms of phase partition are the quasi instantaneous solubilization of pollutants near the coal tar/water interphase, and the diffusion of pollutants within the organic phase or at the interphase which controls the transfer kinetics of pollutants towards the aqueous phase. The dissolution kinetics experimentally observed were therefore correlated to a diffusional model of mass transfer. The formation of a film which increased resistance to mass transfer was also observed at the coal tar/water interphase. This ageing phenomenon of the coal tar/water interphase was found to be an important aspect which can have a significant influence on the long term fate of coal tar in soils or subsoils, as well as on soil remediation techniques.

A Log-Normal Distribution Model for the Molecular Weight of Aquatic Fulvic Acids

The molecular weight of humic substances influences their proton and metal binding, organic pollutant partitioning, adsorption onto minerals and activated carbon, and behavior during water treatment. We propose a log-normal model for the molecular weight distribution in aquatic fulvic acids to provide a conceptual framework for studying these size effects. The normal curve mean and standard deviation are readily calculated from measured Mn and Mw and vary from 2.7 to 3 for the means and from 0.28 to 0.37 for the standard deviations for typical aquatic fulvic acids. The model is consistent with several types of molecular weight data, including the shapes of high-pressure size-exclusion chromatography (HP-SEC) peaks. Applications of the model to electrostatic interactions, pollutant solubilization, and adsorption are explored in illustrative calculations.

ADSORPTION AND FRACTIONATION OF A MUCK FULVIC ACID ON KAOLINITE AND GOETHITE AT pH 3.7, 6, AND 8

Molecular weight (MW) of humic materials is a key factor controlling proton and metal binding and organic pollutant partitioning. Several studies have suggested preferential adsorption of higher MW, more aromatic moieties to mineral surfaces; quantification of such processes is fundamental to develo

Evaluation of the partitioning of hydrophobic pollutants between aquatic and solid phases in natural systems

Sorption partition coefficients are commonly used to quantify the distribution of organic pollutants between the aqueous and particulate phase of natural aqueous systems. Lotse et al. [6] found a significant increase in partitioning as the solid concentration decreases. Pollutants with larger partition coefficients have a more pronounced effect on the observed partitioning with changes in solid concentration. In the present study, partition coefficients for sediment-water systems were determined using Second Songhua River sediment. The effect of added DOC (using 12.5 ppm fulvic acid) and centrifuge speed on the partitioning of pollutants were studied. Dissolved organic carbon (DOC), nonsettling micro-particles (NSPs) and light absorption were also analyzed. From the results, the solids effect can be attributed to a transfer of solute-binding material from the solid phase to the liquid phase during the course of the partitioning procedure. This material, whether DOC or NSPs in nature, was not removed from the liquid phase during the separation procedure and possessed a higher capacity for the solute than the water itself. It increases the amount of solute in the liquid phase and makes the observed partition coefficients decrease. The true partition coefficients ( K oc t) of 11 constituents have been calculated from the observed partition coefficients at different solid concentrations. The values of K oc t approach a constant and cannot be affected by the solid concentration. It supports the explanation describing the effect of solids.

Comparative study of multimedia modeling for dynamic partitioning of fossil fuels-related pollutants

Health-based risk assessments have uncertainties in many areas. These uncertainties necessitate the use of assumptions which are required to err on the side of public health protection. One source of uncertainty in risk assessment is the extent of human exposure to pollutants in various media such as air, water, soil, sediment and biota. The pollutant concentrations in these media can be simulated through multimedia modeling of the complex physical, chemical, and biological processes that govern the fate and transport of the pollutants. By reducing uncertainty (which often leads to conservatism) and providing realistic scenarios, multimedia modeling can help develop operating and control strategies which will minimize expenditures of societal resources without compromising environmental quality and public health. Multimedia calculations are complex. A variety of methodologies and models have been proposed in the last two decades. However, the task has been made easier in recent years because of the advent in personal computers and the development of PC-based computer software. Two of such softwares are the fugacity models and the spatial multimedia compartmental (SMCM) model. In this paper, these two models were applied to study the dynamic partitioning of several fossil fuels-related pollutants in different locations. The transient behavior of a pollutant resulting from an environmental perturbation was also examined. Finally, the capabilities and limitations of these models were compared from a user's point of view.

Managing hazardous air pollutants: state of the art

Managing hazardous air pollutants: state of the art

Speciation and partitioning of priority organic contaminants in estuarine waters

The main parameters influencing the speciation and partitioning of priority organic contaminants in estuaries are discussed with particular consideration being given to the association of contaminants with colloidal material. Partitioning and speciation are factors that influence the persistence, transport, bioavailability and toxicity of organic contaminants in natural waters. However, most data on aquatic partitioning processes are based on the extrapolation of soil data and there is a need for more information on the partitioning of priority pollutants in estuaries in order that their transport, fate and toxicity may be adequately assessed. In general, water quality studies concerned with organic contaminants either report total concentrations or at best differentiate between ‘dissolved’ and particulate forms based on filtration. The concept and importance of solution phase speciation is well established for trace metals and it is generally accepted that for many metals it is the free metal ion that is the bioavailable and hence the toxic form. Several reports suggest that the same is true for organic contaminants, i.e. association with particulates, colloidal material and macromolecular organics reduces bioavailability and toxicity. Physicochemical data for contaminant—particle interactions in aqueous systems are essential for the development of effective environmental management models. Work on the partitioning behaviour of organic contaminants has been focused on compounds selected from the UK Red List, i.e. atrazine and gamma-hexachlorocyclohexane in estuarine waters. Particular emphasis has been placed on evaluating the importance of pesticide binding to naturally occurring colloids. The influence of physicochemical parameters such as salinity and suspended solids' concentration on contaminant partitioning behaviour has also been established. Data on the association of specific priority organic contaminants with filterable organic macromolecules or colloids are discussed.

The Role of Suspended Matter in Assessing the Assimilative Capacity Case Study of Two Estuaries in the Adriatic Sea

Abstract Suspended particulate matter has been studied in two Adriatic river mouths to assess its role as a transport vehicle for waste disposal into the Adriatic sea. The larger of the two, the Adige River (northwestern Adriatic coast, Italy), carries large quantities of solids and builds up a prodelta. the Krka River (eastern Adriatic coast, Croatia, Yugoslavia) is a typical karst river, and carries small quantities of suspended matter, since it drains carbonate terrains. The resulting disposal of contaminants into the Adriatic sea is largely governed by the adsorption/desorption processes occurring in the estuarine mixing region. Surface adsorption properties, the specific surface area, and the nature and reactivity of the organic film coating determine the partitioning of pollutants between the dissolved and particulate state. The observations reported point to the key role of particulates in transport of pollutants from land to sea. the concept of the assimilative capacity of the estuarine area requires detailed scientific knowledge on the geochemical behaviour of particulates. In the Adige River mouth, lead, chromium, zinc, and nickel are accumulated in the prodelta sediments, and thus the loading of the sea with these metals is diminished, whereas in the Krka River estuary, desorption and mobilization of some trace metals occurs.

Effects of water content and temperature on equilibrium distribution of organic pollutants in unsaturated soil

The purpose of this research was to quantify the effects of water content (0.3 to 0.75% for sand, and 0.4 to 1.25% for silt-clay) and temperature (4 to 40 °C) on the equilibrium distribution of the priority pollutants, dichloromethane and 1,1,1-trichloroethane in dry Korean decomposed granite soil. The values of effective partition coefficient (Keff) were largely decreased as the water content increased. Organic pollutant partitioning in dry soil is composed of both water saturated site and dry site in sorbent, and dry site which has high partition coefficient, is reduced as the water content increases. As the temperature increased, the Keff values decreased, and this effect was magnified at lower water contents. The values of Keff were correlated better with the estimated values using proposed model. Therefore, in the analysis of distribution and transport of pollutant in unsaturated soil, the effects of water content and temperature on the partitioning should be considered.

On the Role of Fine Sediment Behaviour in Pollutant Transfer Modelling

The role played by fine cohesive sediment in the transport and recycling of pollutants arises from the often reversible partition of pollutants between the dissolved phase and surface sorbed phase. Adequate prediction requires that a realistic understanding of the physical behaviour of the fine sediment population of an area is coupled with the kinetics of the sorbtion/desorbtion equilibria at crucial stages in the fine sediment transport cycle. This paper examines the physical basis underlying the prediction of fine sediment transport, identifying processes and phenomena which are important in affecting predictions. Parameterisation of source and sink terms are seen to be areas of great uncertainty and model calibration requires the deployment of new, but available, technology.

Numerical studies of acidification processes within and below clouds with a flow-through chemical reactor model

A flow-through chemical reactor model has been exercised to assess the importance of various oxidation reactions and cloud processes on wet removal and redistribution of atmospheric pollutants and to investigate the effect of in-cloud acidification on precipitation chemistry at the surface. Preliminary results indicate that in-cloud acidification accounts for more than 60% of the wet deposited acids derived from acidification of initial SO 2, that 42–57% of water-soluble, non-reactive NH 3 and HNO 3 are removed by wet deposition. The pseudo-first-order conversion rate of SO 2 to SO 4 2− ranges from 3 to 25% h −1 depending on initial and boundary conditions. Sensitivity studies have been carried out to test the importance of time evolution of clouds on partitioning of pollutants in the atmosphere and to investigate the variability of precipitation chemistry due to changes in rate constants. The distributions of NH 3 and HNO 3 are found to be dependent largely on the cloud microphysical parameters, while the distributions of H 2O 2 and SO 2 depend largely on initial conditions of both species. Individual physical and chemical mechanisms can determine the overall rate of sulfate wet deposition at different stages of cloud evolution.

Evaluation of sorptive partitioning of nonionic pollutants in closed systems by headspace analysis

An equilibrium headspace technique is shown to be applicable to the determination of sorption equilibria for the nonionic volatile organic compounds toluene and trichloroethylene (TCE). This procedure avoids the problems inherent in other experimental techniques that directly analyze aqueous phase concentration. Such problems include incomplete solid phase separation and subsequent measurements of solute bound to dissolved or colloidal sorbent as free solute. Sorptive partitioning coefficients may be determined by the headspace procedure in the absence of carrier solvents or knowledge of the aqueous concentration of the volatile compounds of concern. Experiments examining the sorption of toluene and TCE onto humic acids, alumina coated with humic acids, and two soil core samples demonstrated the applicability of the headspace technique to sorption studies.

Effect of solids concentration on the sorptive partitioning of hydrophobic pollutants in aquatic systems

Etude menee sur des sediments du Lac Michigan avec 4 polluants prioritaires hydrophobes: chlorobenzene, naphtolene, trichlorobiphenyle et hexachlorobiphenyle