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Both adsorption and desorption data were used to estimate sorption parameters for phenanthrene with four soils of varying organic carbon content. Adsorption parameters were determined using linear and nonlinear equilibrium models for four different initial concentrations that had equilibrated with each soil for 70 days. Desorption parameters were d...
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Context 1
... hysteresis has been observed in a num- ber of organic solute-geosorbent systems (Table 1) [Pignatello, 1990], and ionizable organic contami- nants such as phenols [Bhandari et al., 1996[Bhandari et al., , 1998] and triazines [Steck et al., 1995]. In many of these studies, adsorption iso- therms were linear, while hysteretic desorption isotherms were nonlinear (Table 1). ...
Context 2
... hysteresis has been observed in a num- ber of organic solute-geosorbent systems (Table 1) [Pignatello, 1990], and ionizable organic contami- nants such as phenols [Bhandari et al., 1996[Bhandari et al., , 1998] and triazines [Steck et al., 1995]. In many of these studies, adsorption iso- therms were linear, while hysteretic desorption isotherms were nonlinear (Table 1). While some of these differences may have been caused by apparent hysteresis or irreversible adsorption (versus true hysteresis), the common observation in widely varied experimental systems suggests that organic solute ad- sorption and desorption processes are truly different, and this is significant in many environmental settings. ...
Citations
... Although the The sample sizes, solvent volumes, and extraction times used for MAE in this work were generally less than those used in other MAE studies (Barnabas et al., 1995; Lopez Avila et al., 1995 ), but were sufficient at achieving good recoveries as well as reproducible results. The lower recoveries by Soxhlet and MAE of the OPPs, especially from sand, may methods which involve removing non-adsorbed compounds immediately after spiking (Burgos et al., 1999; Kan et al., 1994). In the cases where non-adsorbed compounds are immediately washed off, there is no allowance for slow adsorption of contaminants into the matrix and only immediate adsorption is investigated. ...
The inadvertent ingestion of contaminated soil can be an important source of pesticide exposure, especially in young children. The actual level of a pesticide that is available for absorption into a biological system may be much lower than the overall contamination level due to the interaction of each chemical with the solid matrix. This bioaccessibility is dependent on characteristics of the chemical species as well as the soil type and residence time of the compound in the soil. In an effort to improve understanding of this phenomenon, we report a comparison of the recoveries of pesticides spiked into soil and two model solids using different analyti- cal extraction techniques: Soxhlet extraction, microwave-assisted extraction with an organic solvent (MAE), and microwave extraction using water as a solvent (WME). The efficiency of each technique is compared to the maximum bioaccessible fraction determined by a physiologically based extraction test (PBET). Recoveries by Soxhlet and MAE are shown to be in good agreement with each other, but do not predict the bioaccessible fraction. Recoveries by WME, however, are in agreement with bioaccessible fractions of all pesticides and soil types studied. WME has the potential to be useful in bioavailability studies.
... In the desorption step, the sorbed solute on the solid phase was allowed to desorb to background solution that was initially free of solute. The contents of PHE in the solution were measured, and desorbed PHE was calculated accordingly [29]. ...
... Both linear and non-linear sorption isotherms have been reported for sorption of PHE to soils and sediments in aqueous systems [18,29,34,52,53]. In our study, linear isotherms are considered to primarily result from partitioning (dissolution) of PHE into the three-dimensional matrix of DOM-MMT. ...
To investigate the effect of dissolved organic matter (DOM) on the adsorption of phenanthrene (PHE) by montmorillonite (MMT), organic clay complex was prepared by associating montmorillonite with DOM extracted from landfill leachate. Both the raw MMT, DOM, and MMT complex (DOM-MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photo-emission spectroscopy (XPS), and scanning electron microscope (SEM). Batch adsorption studies were carried out on the adsorption of PHE as a function of contact time, temperature, and adsorbent dose. The sorption of PHE on complex was rapid, and the kinetics could be described well by the Pseudo-first-order model (R(2)>0.99), with an equilibrium time of 120 min. The adsorption isotherm was in good agreement with the Henry equation and Freundlich equation. Also, thermodynamic studies showed that the adsorption process was exothermic and spontaneous in nature. Compared with MMT, the adsorption capacity of DOM-MMT complex for PHE was greatly enhanced. The effects of DOM on PHE sorption by MMT may be attributed to the changes in the surface structure, the specific surface area, the hydrophobic property, and the average pore size of MMT. A series of atomistic simulations were performed to capture the structural and functional qualities observed experimentally.
... Des isothermes de sorption peuvent alors être tracées et elles sont utilisées pour prédire la rétention (et donc le transport) des polluants dans les sols. De nombreuses études ont été effectuées pour quantifier la rétention des HAP dans les sols selon ce principe (par exemple Means et al., 1980 ;Kimble et Chin, 1994 ;Burgos et al., 1996;Chiou et al., 1998 ;Burgos et al., 1999). Ces études se font toujours avec les HAP les plus légers, et en particulier le naphtalène, le phénanthrène, le pyrène et l'anthracène. ...
Ce travail visait à évaluer le transport d'hydrocarbures aromatiques polycycliques (HAP) et de métaux dans des sols multi pollués, en s'intéressant plus particulièrement au couplage transport-réaction dans la zone non saturée du sol, selon deux axes de travail. En premier lieu, puisque de nombreux sites industriels sont multi pollués, nous avons choisi d'étudier l'influence des métaux sur la sorption des HAP et vice versa en système modèle. Nous avons montré que lors d'une pollution simultanée par du fluoranthène et du zinc, ce dernier est beaucoup moins retenu que lorsqu'il est présent seul et peut donc migrer plus facilement vers la nappe phréatique. Le plomb, quant à lui, est plus fortement retenu en présence de fluoranthène. En revanche, l'effet des métaux sur la rétention du fluoranthène est plus limité. En second lieu, nous avons évalué le transport des HAP et des métaux dans une terre d'une ancienne cokerie lorraine à plusieurs échelles : en colonne de laboratoire en conditions saturées et non saturées ainsi qu'en lysimètre de terrain, afin d'évaluer le pouvoir prédictif des sytèmes de laboratoire. Nous avons montré que les expériences en colonne de laboratoire surestiment la sortie des HAP telle qu'elle a lieu sur le terrain. En revanche, la sortie des métaux est bien prédite par de telles expériences. Mais le lysimètre ne peut pas être utilisé lors d'études de risque puisqu'il demande des durées d'expériences de plusieurs années afin d'avoir une vue globale des phénomènes qui s'y produisent. C'est pourquoi nous avons conçu un système original au laboratoire, capable d'évaluer leur transport conformément à ce qui se passe sur le terrain
Description
The latest volume in this ASTM series explores the advancements in the field of environmental toxicology and risk assessment, including methods of carrying scientific findings forward to sound policy decisions. 25 papers in 6 sections cover:
Aquatic Toxicology--examines the ionic composition in water used in toxicity tests and how that impacts on metal toxicity; how modified PAHs impact on EROD levels; how UV radiation in natural aquatic settings impacts on photosynthesis in phytoplankton; and ship channel contaminant assessment.
Interface Between Policy, Science and Risk Assessment--addresses the use appropriate data in environmental modeling; statistical procedures to find the real ecological risk drivers; comparisons of fish and human toxicity; and statistical evaluation of terrestrial non-target organisms.
ASTM Standards and Their Applications--focuses on how ASTM standards can be used in science and policy.
Biomonitoring of Sediments and Aquatic Systems--deals with an extension of the Microtox assay; assessing PAH bioavailability at off-shore oil wells; a new powerful molecular bioindicator; a comparison of EROD and fibronectin levels; and toxicity of photomodified polycyclic aromatic hydrocarbon mixtures in contaminated sediments.
Current Issues In Soil Toxicity and Remediation--discusses how important the evaluation of soil toxicity is becoming, and how such contaminated sites can be cleaned for reuse.
New Directions in Environmental Assessment and Recovery--explores how to use environmental assessment data to make decisions on risk and restoration.
Petroleum hydrocarbons are hydrophobic and tend to adhere to soil when released into the environment. Desorption of the contaminant from soil is necessary for most remediation technologies. In subsurface and for in-situ remediation, the dominant desorption mechanism is back diffusion. In this study, three tests were conducted to establish sorption and desorption kinetics for phenanthrene as a contaminant and kaolinite as a soil matrix. Sorption isotherm tests were conducted at temperatures of 14, 22, and 30 °C using six phenanthrene solution containing concentrations from 300 to 800 μg/L. Freundlich equation constant, Kf, values of 0.147, 0.133, and 0.109 μgLn/g(1+n) were determined for the three temperatures. Desorption tests were conducted using phenanthrene-free solution to determine desorption parameters at room temperature (∼22 °C). In addition, two test series were performed to compare phenanthrene desorption by hydraulic and electroosmotic flows at room temperature. A fixed wall hydraulic permeability apparatus was used to generate a hydraulic flow rate of 1.4 × 10-3 mL/s at a pressure of 260 kPa, while a low level direct current density (0.3-0.43 mA/cm2) was applied to generate electroosmotic flow rate equivalent to the hydraulic flow. The phenanthrene concentration in effluent samples after desorption by electroosmotic flow was found to be three to four times the concentration after desorption by hydraulic flow. Moreover, the power required in the hydraulic flow test was three orders of magnitude higher than the consumed power in the electrokinetic flow test. These results show that phenanthrene desorption by electroosmotic flow is more efficient than by hydraulic flow.
Organic chemical exposure in soil toxicity tests and in ecological risk assessment of terrestrial systems is usually expressed as the total chemical measured. Possible alternatives to total chemical measures of organic chemical bioavailability and exposure include body residues in test organisms, soil extraction with selective solvents, and passive sampling devices (PSDs) as biological surrogates. Semipermeable membrane devices (SPMDs) offer potential as a biological surrogate in soil systems. Solid-phase microextraction (SPME) fibers are a rapid and sensitive means for detecting PAHs in soil and have the advantage of not requiring solvent extraction of soil. The objective of this study was to compare chemical uptake and residues in earthworms, SPMDs, and SPMEs exposed in artificial soil spiked with phenanthrene (PHE). Bioavailable PHE, as assessed by mortality and PHE body residues, varied dramatically with soil organic matter content. Both SPMEs and SPMDs could discriminate differences in PHE availability between treatments. However, PHE levels measured using SPMEs were more precise and allowed discrimination between toxic and non-toxic levels of PHE, while PHE levels in SPMDs were too variable for use as a predictive tool.
In equilibrium, the amount of a dissolved component, N, adsorbed on soil or aquifer material and the concentration of this component in the liquid phase, C, at a given temperature and pressure satisfy a unique relationship N = f(C), referred to as the (single-component) sorption isotherm (model). Empirical coefficients of the sorption isotherms are determined by the energy of the different adsorption sites and the nature of liquid/solid interactions (Venitcianov and Rubinshtein 1983). Under certain conditions, sorption processes are only partially reversible, so the desorption parameters may differ, in one direction or another, from the sorption parameters. This is a manifestation of sorption hysteresis (Sect. 19.1.3).
The objective of this study was to investigate the effects of compound aging in soil, bacterial type inoculated, and the number of desorption steps on the biodegradation of phenanthrene and pyrene. A batch biodegradation study was conducted in a 3 2 3 Latin Square design to achieve this objective. The results indicated that only the number of desorption steps used yielded a statistical difference ( p < .05). To compare the significance of the desorption effects in conjunction with compound aging and bacteria type, the Tukey's honestly significant difference test ( f = 0.05) was performed. As expected, the zero-time desorption step yielded a more significant increase in biodegradation than two- and six-time desorption steps which had similar results. Furthermore, the presence of a recalcitrant cosolute (pyrene) had a detrimental effect on phenanthrene degradation with bacteria that had been acclimated with phenanthrene as the sole carbon source. Increases in the number of desorption steps decreased the toxicity of pyrene to the phenanthrene-degraders. As anticipated, the lack of substrate availability yielded limited microbial growth and subsequent contaminant biodegradation.
