Behavior Of Organic Contaminants Research Articles

Partitioning Behavior of Organic Contaminants in Carbon Storage Environments: A Critical Review

Carbon capture and storage is a promising strategy for mitigating the CO(2) contribution to global climate change. The large scale implementation of the technology mandates better understanding of the risks associated with CO(2) injection into geologic formations and the subsequent interactions with groundwater resources. The injected supercritical CO(2) (sc-CO(2)) is a nonpolar solvent that can potentially mobilize organic compounds that exist at residual saturation in the formation. Here, we review the partitioning behavior of selected organic compounds typically found in depleted oil reservoirs in the residual oil-brine-sc-CO(2) system under carbon storage conditions. The solubility of pure phase organic compounds in sc-CO(2) and partitioning of organic compounds between water and sc-CO(2) follow trends predicted based on thermodynamics. Compounds with high volatility and low aqueous solubility have the highest potential to partition to sc-CO(2). The partitioning of low volatility compounds to sc-CO(2) can be enhanced by cosolvency due to the presence of higher volatility compounds in the sc-CO(2). The effect of temperature, pressure, salinity, pH, and dissolution of water molecules into sc-CO(2) on the partitioning behavior of organic compounds in the residual oil-brine-sc-CO(2) system is discussed. Data gaps and research needs for models to predict the partitioning of organic compounds in brines and from complex mixtures of oils are presented. Models need to be able to better incorporate the effect of salinity and cosolvency, which will require more experimental data from key classes of organic compounds.

Salting-Out Effect in Aqueous NaCl Solutions: Trends with Size and Polarity of Solute Molecules

Salting-out in aqueous NaCl solutions is relevant for the environmental behavior of organic contaminants. In this study, Setschenow (or salting-out) coefficients (K(s) [M(-1)]) for 43 diverse neutral compounds in NaCl solutions were measured using a shared headspace passive dosing method and a negligible depletion solid phase microextraction technique. The results were used to calibrate and evaluate estimation models for K(s). The molar volume of the solute correlated only moderately with K(s) (R(2) = 0.49, SD = 0.052). The polyparameter linear free energy relationship (pp-LFER) model that uses five compound descriptors resulted in a more accurate fit to our data (R(2) = 0.83, SD = 0.031). The pp-LFER analysis revealed that Na(+) and Cl(-) in aqueous solutions increase the cavity formation energy cost and the polar interaction energies toward neutral organic solutes. Accordingly, the salting-out effect increases with the size and decreases with the polarity of the solute molecule. COSMO-RS, a quantum mechanics-based fully predictive model, generally overpredicted the experimental K(s), but the predicted values were moderately correlated with the experimental values (R(2) = 0.66, SD = 0.042). Literature data (n = 93) were predicted by the calibrated pp-LFER and COSMO-RS models with root mean squared errors of 0.047 and 0.050, respectively. This study offers prediction models to estimate K(s), allowing implementation of the salting-out effect in contaminant fate models, linkage of various partition coefficients (such as air-water, sediment-water, and extraction phase-water partition coefficients) measured for fresh water and seawater, and estimation of enhancement of extraction efficiency in analytical procedures.

Norfloxacin Sorption and Its Thermodynamics on Surface-Modified Carbon Nanotubes

Adsorption on carbon nanotubes (CNTs) may affect the environmental behavior of organic contaminants including antibiotics. In this study, sorption of norfloxacin (NOR) onto graphitized multiwall CNTs (G-CNTs), carboxylated multiwall CNTs (C-CNTs), hydroxylated multiwall CNTs (H-CNTs), and activated carbon (AC) was investigated. All sorption isotherms were highly nonlinear and were fitted well by Freundlich and Polanyi-Manes models. AC showed the highest NOR sorption capacity because of its highest surface area. H-CNTs had much higher NOR sorption than C-CNTs, and the pi-pi electron donor-acceptor (EDA) interactions could explain the distinction between the two types of CNTs. Comparison of sorption coefficients at different pHs indicates that hydrophobic and electrostatic interaction also played major roles in sorption of NOR on CNTs. Furthermore, high sorption capacity and hysteresis of NOR on CNTs were demonstrated in this study, which needs to be considered for predicting environmental risks of CNTs and NOR. The results from thermodynamic analysis show that sorption of NOR on AC and CNTs was thermodynamically favorable and generally endothermic. Sorption site energy analysis illustrates a distribution of sorption energy, consistent with nonlinear isotherms, which indicates the heterogeneous sites on CNTs for NOR adsorption.

Compound-Specific Factors Influencing Sorption Nonlinearity in Natural Organic Matter

Nonlinear sorption by natural organic matter may have a significant impact on the behavior of organic contaminants in soils and sediments. This study presents a molecular probe approach based on linear solvation energy relationships (LSERs) to identify and quantify the molecular interactions causing concentration-dependent sorption and proposes estimation methods for sorption nonlinearities. Sorption isotherms ranging over concentrations of more than 4 orders of magnitude were determined in batch systems for 23 and 16 chemically diverse probe compounds in a lignite sample and a peat soil, respectively. Each sorbent showed characteristic nonlinear sorption with Freundlich exponents (1/n) being 0.7-1. The LSER-based analysis revealed that the strength of nonspecific interactions did not vary with concentration for both sorbents. In lignite, specific interactions did not affect sorption nonlinearity either, suggesting that compound-independent factors of lignite were responsible for the nonlinear sorption. In the peat soil, by contrast, the specific interactions related to the solute polarizability/dipolarity parameter (S) decreased with increasing concentration. Consequently, compounds of higher S values were more susceptible to nonlinear sorption in the peat soil. Phenol probes have shown that hydrogen bond donating properties of sorbate compounds have a substantial impact on the overall strength of sorption with organic matter, but no significant influence on sorption nonlinearity. Heterocyclic aromatic compounds appear to undergo additional interactions that are not accounted for by the LSER. These additional interactions considerably enhance both sorption capacity and nonlinearity.

Impact of Black Carbon in the Extraction and Mineralization of Phenanthrene in Soil

During the past century, increased biomass burning and fossil fuel consumption have drastically increased the input of black carbon (BC) into the environment, and that has been shown to influence the behavior of organic contaminants in soil. A study was conducted to investigate the effects of BC on the relationship between aqueous hydroxypropyl-beta-cyclodextrin (HPCD) extraction and microbial mineralization (bioaccessibility) of 14C-phenanthrene (10 mg kg(-1)) in four soils amended with 0, 0.1, 0.5, 1, 2.5, and 5% (% dry wt soil) activated charcoal, a type of BC. Mineralisation was monitored over 20 d incubation, within respirometric assays, using an inoculum containing a phenanthrene-degrading pseudomonad and compared to HPCD extraction (24 h) using 50 mM aqueous solution; analyses were conducted after 1, 25, 50, and 100 d soil-phenanthrene contact time. Statistical analyses revealed that for each soil the addition of BC led to significant (P < 0.001) reductions in both HPCD extractability and microbial mineralization. Linear correlations for BC concentrations of 0% (r2 = 0.95; slope = 0.89) and 0.1% (r2 = 0.67; slope = 0.95) revealed a highly significant (P < 0.01) relationship between HPCD extractability and total mineralization (20 d), indicating a direct prediction of phenanthrene bioaccessibility by HPCD. However, in soils amended with 0.5, 1, 2.5, and 5% BC exhibited r2 values ranging 0.51-0.13 and slopes of 2.19-12.73. This study has shown that BC strongly sorbs phenanthrene causing reductions in extractability and, to a lesser extent, bioaccessibility to degrading microorganisms.

Influences of preparative methods of humic acids on the sorption of 2,4,6-trichlorophenol

Humic acids (HAs) are a major component of soil organic matter which strongly affects the sorption behavior of organic contaminants in soils. To assess the sorption–desorption characteristics of organic compounds on HAs, the organic adsorbent is usually isolated using an acid-base extraction method followed by air-drying or freeze-drying. In this study, a peat soil from the Yangming mountain area of Taiwan was sampled and repeatedly extracted followed by either air-drying or a non-drying treatment (denoted DHAs and NDHAs, respectively). The sorption of 2,4,6-TCP on HAs was evaluated using the batch method. Kinetic sorption results indicated that DHAs exhibited a two-step first-order sorption behavior, involving a rapid sorption followed by a slow sorption. The slow sorption may be attributed to the diffusion of 2,4,6-TCP through the condensed aromatic domains of HAs. On the contrary, the sorption of 2,4,6-TCP on NDHAs was extremely rapid, and the sorption data did not fit existing kinetic models. Each HA sample exhibited a nonlinear sorption isotherm. Sorption nonlinearity (represented by Freundlich N values) and K oc had a positive relationship with aliphaticity for DHAs; however, nonlinearity and K oc correlated positively with aromaticity when NDHAs adsorbents were used. We conclude that the air-drying technique may artificially create a more condensed area, which strongly affects the sorption characteristics of HAs. Thus, an incorrect evaluation of the sorption capacity and its relationship with the chemical composition of HAs would arise following use of the air-drying method.

Performance of the partition-limited model on predicting ryegrass uptake of polycyclic aromatic hydrocarbons

Accurate modeling of the uptake and accumulation behavior of organic contaminants like polycyclic aromatic hydrocarbons (PAHs) in plants is essential to assess crop contamination and subsequent human exposure. In this study, the performance of a partition-limited model on predicting ryegrass uptake of PAHs (acenaphthene, fluorene, phenanthrene and pyrene) from water was evaluated and the major factors were examined. It was found that model predictions of PAH concentrations in roots and shoots of ryegrass were all within an order of magnitude of the observed values with the differences between estimated and measured concentrations less than 42.1% for roots and 78.4% for shoots. Since the model considered soil/water–plant pathway only, it was inevitable that simulated concentrations in shoots suffered a bigger error than those in roots due to the influence of foliar uptake, the other important pathway for PAHs. If the impact of foliar uptake was excluded, the accuracy of simulated shoot concentrations would be greatly enhanced, with the maximum prediction error reduced from 78.4% to 47.1% for pyrene. Other factors aside from foliar uptake were also examined, including aqueous PAH concentrations, uptake time, plant composition and chemical properties. These factors were found to influence the model performance generally through acting on the quasi-equilibrium factor ( α pt). Results from this study substantiated the utility of this partition-limited model for vegetation-uptake assessment, and then provided some testimony valuable for the modification of a model with a better performance.

Analysis of undisturbed layers of a waste deposit landfill – Insights into the transformation and transport of organic contaminants

Comprehensive GC/MS analysis was applied to both the mobile liquid phase (seepage water) and the immobile solid matter of discrete layers derived from a waste deposit landfill. The vertical distribution of organic compounds supports information on the transport, transfer and transformation processes with depth and, consequently, with time. Numerous low molecular weight organic contaminants of natural and xenobiotic origin were identified and partially quantified. Several were selected to act as molecular indicators for different processes. Interpretation of their occurrence and concentration profiles (considering possible waste sources) and their molecular properties allowed us to (i) differentiate immobile and mobile fractions, (ii) reveal restrictions in the vertical transport by transfer processes between particulate and water phase, (iii) identify dynamic accumulations of individual contaminants and (iv) estimate approximate residence times. In addition, intensive degradation processes were pointed out for the natural fraction of the organic matter by way of determination of specific transformation products. Besides the transformation of natural components, transformation of numerous xenobiotics was recognised. In particular, with respect to an important group of contaminants, the phthalate-based plasticisers, a detailed view of (i) the influence of transfer and transport phenomena on transformation processes as well as (ii) the consecutive appearance of different degradation steps in both seepage water and solid waste was pointed out. The information provides a valuable base for the prediction of the long term behaviour of organic contaminants in waste deposit landfills.

Measuring the Release of Organic Contaminants from Melting Snow under Controlled Conditions

The release of organic contaminants from a melting snowpack may result in temporary concentration peaks in receiving water bodies and respective pulse exposure of aquatic organisms. It is thus of considerable interest to gain a mechanistic and quantitative understanding of the processes determining the dynamic behavior of organic chemicals during snowmelt. Uniformly structured and contaminated snow was produced with the help of a newly designed snow gun and exposed to predetermined temperature conditions in a temperature-controlled cold room. The dry density and liquid water content during four freeze-thaw cycles was recorded continuously at different layers within the snowpack using time domain reflectometry, providing information on meltwater production and propagation as well as snow metamorphism. Fractionated meltwater samples were filtered and the dissolved and particle phase analyzed for five polycyclic aromatic hydrocarbons (PAHs) using gas chromatography/ mass spectrometry. The distribution of the PAHs between the dissolved and particulate fractions of the meltwater was strongly related to their hydrophobicity. Particle-bound PAHs were released late during the snowmelt, whereas PAHs in the dissolved phase were released uniformly during a two day melting period. Even though conductivity measurements indicated a preferential early elution of ions in the first meltwater fractions, no such "first flush" behavior was observed for soluble PAH. The developed laboratory-based approach opens up for the first time the possibility of reproducible experiments on organic contaminant behavior in snow. Future experiments will explore, in detail, how the properties of organic chemicals, the physical and chemical properties of the snowpack, and the temperature variations before and during the time of melting interact to determine the timing of chemical release from a snowpack.

Behaviour and assessment of bioavailability of organic contaminants in soil: relevance for risk assessment and remediation

Abstract. Soils contaminated with organic chemicals are now widespread in industrialized and developing countries, and the risk assessment and remediation of such contaminated sites is a priority. However, containment and remediation strategies are complicated in many cases by the range of contaminants present and the historical nature of the contamination. Research has increased our understanding of the behaviour of organic contaminants in soil and the factors that control their behaviour. There is a fundamental need to understand and, where possible, quantify the bioavailable fraction as well as the total concentration of contaminant present in soil: the bioavailable fraction is key to toxicity or biodegradation. To quantify these fractions, a large number of techniques have been employed, ranging from organic and aqueous based solvent extractions to the use of biota. Many studies have been carried out investigating the use of chemical techniques to describe bioavailability, which could be used in the assessment and remediation of contaminated land. The aim of this review is to consider the behaviour of organic contaminants in soil, highlighting issues of bioavailability, and then to discuss the relevance of the various methods for assessing risk and potential remediation of organic contaminants in soil.

Thermomechanical analysis of air-dried whole soil samples

Macromolecular characteristics of organic matter in soil can greatly influence the sorption behavior of organic compounds. Previous investigations of the macromolecular nature of whole soil samples by differential scanning calorimetry (DSC) revealed step transitions in air-dried soil samples, which do not fully mimic typical glass transition behavior. This work further explores these step transitions through a second, independent method: thermomechanical analysis (TMA). TMA was validated with respect to detection, localization, and quantification of the step transitions in whole soil samples. TMA was found to sensitively detect the transitions, indicating sample softening near the step transition ( T g * ) , while localization of T g * by TMA appears to be accurate in pellets only. Quantification via difference between coefficients of initial expansion and final compression, respectively, is favorable for weak transitions, where the sensitivity of DSC is too low to obtain reliable results. Although the nonreversing nature of the step transition is atypical for glass transitions, the observed matrix softening suggests changes in matrix rigidity near T g * . This softening is hypothesized to be associated with water bridging individual soil structural units. The slow, nonreversing changes in soil rigidity are expected to affect the sorption behavior of organic contaminants, and the increase in compressibility further suggests relevance for soil mechanical properties.

Environmental Organic Chemistry, 2nd Edition (Schwarzenback, Rene P.; Gschwend, Philip M.; Imboden, Dieter M.)

This update of the definitive textbook on the fate and behavior of organic contaminants in natural aquatic systems incorporates key features that were missing from the first edition. Qualitative and quantitative problems have been added to each chapter as well as chapters on new topics.

Phenanthrene Sorption to Structurally Modified Humic Acids

Several studies emphasize the importance of soil organic matter characteristics in hydrophobic contaminant sorption and outline the strong dependence of sorption on organic matter aromaticity. In this study, the role of organic matter aromaticity in phenanthrene sorption was investigated using humic acids (HAs) from compost, peat, and soil that were structurally modified by bleaching, hydrolysis, oximation, and subcritical water extraction. The HAs were characterized with cross polarization magic angle spinning carbon-13 nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy and used in batch equilibrations with phenanthrene. Bleaching substantially reduced the aromaticity of the samples whereas the other treatments increased the relative aromaticity. Phenanthrene sorption increased, even though there was a substantial reduction in sorbent aromaticity with some samples. The HAs that exhibited comparable CPMAS 13C NMR spectra and aromaticity did not behave similarly with respect to phenanthrene sorption. When the sorption data (K(oc) values) were correlated to sample aromaticity, the correlation coefficients (r2) did not exceed 0.39. Comparisons with the atomic H to C ratio provided slightly better r2 values (up to 0.54). This study demonstrates that macroscopic sorbent characteristics could not explain the observed phenanthrene sorption coefficients, aliphatic structural components of HAs can contribute appreciably to phenanthrene sorption, and organic matter physical conformation may regulate access to organic matter structures. Therefore, the use of only macroscopic sorbent properties, such as aromaticity, to predict and rationalize sorption values cannot solely be used to explain the behavior of organic contaminants in soil environments.

Attenuation of landfill leachate by clay liner materials in laboratory columns, 1. Experimental procedures and behaviour of organic contaminants

The chemical attenuation of natural organic matter and 13 organic micropollutants (BTEX, aromatic hydrocarbons, pesticides, chloro-aromatic and -aliphatic compounds) in methanogenic landfill leachate by two UK clay liner materials was compared in laboratory columns over 15 months. Organic contaminant behaviour was evaluated using a first order decay transport model. Sorption of organic micropollutants by the clay liners was greater (by up to a factor of four) than expected. The organic micropollutants were degraded under different redox conditions and solute half lives varied from 4 to 112 days. Degradation of many organic micropollutants was complex and influenced by the sequential transformation of preferred substrates in the leachate. This cannot be predicted, although the results show that degradation in fieldscale liners will be extensive. Benzene was recalcitrant under the conditions and timespan (> 280 days) of the experiments. Natural organic matter (COD) behaved conservatively in the experiments. Attenuated organic contaminants were not released from the clay liners during flushing with freshwater suggesting that organic micropollutants are permanently sorbed or only slowly desorbed within the experiment. A conceptual model of liner performance is presented. Chemical attenuation of organic pollutants can be included in containment liner design to produce a dual reactive–passive barrier for landfills.

Attenuation of landfill leachate by clay liner materials in laboratory columns, 1. Experimental procedures and behaviour of organic contaminants

The chemical attenuation of natural organic matter and 13 organic micropollutants (BTEX, aromatic hydrocarbons, pesticides, chloro-aromatic and -aliphatic compounds) in methanogenic landfill leachate by two UK clay liner materials was compared in laboratory columns over 15 months. Organic contaminant behaviour was evaluated using a first order decay transport model. Sorption of organic micropollutants by the clay liners was greater (by up to a factor of four) than expected. The organic micropollutants were degraded under different redox conditions and solute half lives varied from 4 to 112 days. Degradation of many organic micropollutants was complex and influenced by the sequential transformation of preferred substrates in the leachate. This cannot be predicted, although the results show that degradation in fieldscale liners will be extensive. Benzene was recalcitrant under the conditions and timespan (&gt; 280 days) of the experiments. Natural organic matter (COD) behaved conservatively in the experiments. Attenuated organic contaminants were not released from the clay liners during flushing with freshwater suggesting that organic micropollutants are permanently sorbed or only slowly desorbed within the experiment. A conceptual model of liner performance is presented. Chemical attenuation of organic pollutants can be included in containment liner design to produce a dual reactive-passive barrier for landfills.

Adsorption Behavior of Organic Contaminants on a Silicon Wafer Surface

The adsorption behavior of organic contaminants adsorbed onto silicon wafer surfaces was studied. Contaminants result from the presence of volatile organic contaminants in clean room environments and in plastic storage boxes. The contaminants on the wafers were collected by dissolving them in solvent and were characterized by gas chromatography‐mass spectroscopy analysis. It was found that organic contaminants increase in quantity over time. When the contaminants were examined in detail, it was found that the behavior of each contaminant varied with differences in their chemical properties. Whereas the organic contaminants having a low boiling point tended to be adsorbed immediately, those having a high boiling point tended to be adsorbed over a longer exposure time. It is assumed that the organic contaminants having a low boiling point were being replaced by those with a higher boiling point. © 1999 The Electrochemical Society. All rights reserved.

Perspectives in environmental chemistry

Section I: Environmental Chemistry of Condensed Phases. The Solid-Water Interface in Natural Systems. An Overview of Environmental Colloids. Environmental Chemistry of Trace Metals. Metal-Catalyzed Hydrolysis of Organic Contaminants in Aquatic Environments. The Chemistry and Geochemistry of Natural Organic Matter. Assessing the Dynamic Behavior of Organic Contaminants in Natural Waters. Correlation Analysis of Environmental Reactivity of Organic Substances. Photolysis of Organics in the Environment. Microbiologically Mediated Reactions in Aquatic Systems. Section II: Atmospheric Environmental Chemistry. Oxidant Formation in the Troposphere. The Tropospheric Aerosol and Its Role in Atmospheric Chemistry. Why Carbon Dioxide from Fossil Fuel Burning Won't Go Away. Stratospheric Chemistry-Perspectives in Environmental Chemistry. Laboratory Studies of Heterogeneous Chemistry in the Stratosphere. The Stratospheric Aerosol and Its Impact on Stratospheric Chemistry. Chemical-Transport Models of the Atmosphere. Section III: Applied Environmental Chemistry. Samply Collection and Handling of Environmental Matrices. Trace Metal-Phytoplankton Interactions in Marine Systems. Atmosphere-Water-Rock Interactions As Observed in Alpine Lakes. Passive Bioremediation of Metals and Inorganic Contaminants

Partitioning of hydrophobic contaminants in the vadose zone in the presence of a nonaqueous phase

Partitioning behavior of organic contaminants in the vadose zone may be influenced by the presence of a nonaqueous phase liquid (NAPL). The bulk NAPL phase not only serves as a sink for hydrophobic contaminants but may also cover a significant fraction of the soil surface, reducing the surface area available for vapor-solid adsorption. Experiments were carried out to examine the applicability of binary partitioning parameters when applied to a multiphase system. Dodecane was used as the model NAPL phase, while toluene and benzene were used as the model hydrophobic contaminants. Several soil types and water contents were examined. Results indicated that two-phase equilibrium parameters were sufficient to predict partitioning among the various phases if fractional soil surface coverage by each phase was considered. A previously developed model was extended to account for the presence of NAPL and was used to describe the multiphase contaminant partitioning presented in this work.

Sources, behaviour and fate of organic contaminants during sewage treatment and in sewage sludges

Recent concern over the environmental impact of sewage sludge application to agricultural land has drawn particular attention to the wide range of organic contaminants that may enter sewage treatment processes and persist in biosolids for disposal. This paper discusses processes influencing the fate and behaviour of organic contaminants during wastewater treatment and reviews literature relating to specific contaminants identified in sewage sludge. The difficulties associated with the development of specific methods for the analysis of trace residues of organic contaminants in complex matrices such as sludge are discussed. Some potential issues relating to impact of sewage sludge disposed to agricultural land are also considered.

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.