Progress 10/01/00 to 09/30/05
Outputs
Studies have been carried out to characterize the molecular interactions between nonionic organic compounds and organic soil constituents, including humic substances and black carbon, and to quantify the link between sorption and bioavailability. Detailed sorption studies were conducted on whole soils, a peat soil, soil humic acids (HA), Al-crosslinked HA, and a brown coal. These included construction of highly detailed isotherms, competitive sorption experiments, evaluation of irreversible behavior (hysteresis phenomena and the conditioning effect), and structure-activity relationships. The results overall indicate that the OM phase of all materials is in a glassy state. Characteristically the glassy state includes a partition domain and a micropore-filling (hole) domain. The shapes of the isotherms and the influence of crosslinking generally agree with this model. Solutes show a 15-20 kJ/mole preference for hole sites. Irreversible sorption is a result of pore
expansion by the incoming solute that is irreversible on the timescale of the experiment. A new, thermodynamically-based index of irreversibility was derived and applied to several systems. Isotope-exchange experiments carried out at both the sorption and desorption points of a hysteretic cycle at constant bulk chemical concentration verified true, as opposed to artificially-caused, hysteresis. Comparison of sorption/desorption rates of the tracer with the bulk chemical gave further evidence of structural changes occurring in the solid during uptake/release. The conditioning effect (enhanced repeat sorption) was observed generally for the SOM solids but not a rubbery polymer. Annealing of the conditioned solid promoted relaxation as manifested by a trend toward the original distribution coefficient. Pi-pi electron donor-acceptor (EDA) complexes were demonstrated between relevant donor/acceptor aromatic compounds and model compounds representing the corresponding acceptor/donor moiety
in humic substances. These interactions take place in water, as well as in organic solvents. The increase in sorption by SOM of pi electron rich solutes with decreasing pH was consistent with pi-pi EDA between the solute and polycarboxy-substituted or charged N-containing aromatic rings in SOM. Sorption of aromatic compounds on black carbon (wood char) was consistent with pi-pi EDA interactions at the graphene surface. A polyparameter free energy relationship was derived and applied to three high-OC content soils. It revealed the importance of hydrophobic effects, dipolar/dipolarizability (D/P) effects, and (where possible) H-bonding and pi-pi EDA forces. The relative contributions of these forces is concentration dependent. Kinetic and thermodynamic studies validated use of Tenax as an infinite and instantaneous sink for desorbed chemicals in bioavailability studies. Biotransformation of 15 PAH compounds present in a coal tar contaminated soil by indigenous organisms was dramatically
enhanced by adding inorganic macro- and micronutrients. Nutrient-enhanced biotransformation outpaced maximum rates of desorption to Tenax in sterile controls, suggesting that indigenous organisms can facilitate desorption.
Impacts
The results provide compelling evidence for the glassy character of SOM and support the irreversible hole expansion/hole creation mechanism of hysteresis. This advances our understanding of the mechanism of sorption. Pi-pi interactions are possible whenever strongly electron poor and strongly electron rich aromatic or other highly conjugated structures approach in a fact-to-face orientation. Such structures are common to many pesticides and are present in various components of soil organic matter. Humic substances contain both pi-acceptor and pi-donor subunits. This study has presented the first evidence that pi-pi interactions are likely in SOM and black carbon. The LFER emphasizes the importance of D/P effects on sorption and indicates that SOM aromatic content more than polarity dictates D/P effects. It further indicates that molecules fill sites of progressively greater hydrophilic character. The coal tar biodegradation study indicates the potential of organisms to
facilitate bioavailability of contaminants in soils. The results of this project are relevant at a fundamental level to agricultural and other activities that result in contact of chemicals with soil. They provide a better understanding of the molecular-level interactions of chemicals with soils.
Publications
- J. Li, J.J. Pignatello, B.F. Smets, D. Grasso, and E. Monserrate Bench-scale Evaluation of In Situ Bioremediation Strategies for Soil at a Former Manufactured Gas Plant Site, Environ. Toxicol. Chem. 24: 741-749 (2005).
- M. Sander and J.J. Pignatello, Characterization of Charcoal Sorption Sites for Aromatic Compounds: Insights Drawn from Single-Solute and Bi-Solute Competitive Experiments, Environ. Sci. Technol., 39: 1606-1615 (2005).
- D. Zhu and J.J. Pignatello, Characterization of Aromatic Compound Sorptive Interactions with Black Carbon (charcoal) Assisted by Graphite as a Model Sorbent, Environ. Sci. Technol., 39: 2033-2041 (2005).
- S. Kwon and J.J. Pignatello, Effect of Natural Organic Substances on the Surface and Adsorptive Properties of Environmental Black Carbon (Char): Pseudo Pore Blockage by Model Lipid Components and Its Implications for N2-Probed Surface Properties of Natural Sorbents., Environ. Sci. Technol., 39: 7932-7939 (2005).
- D. Zhao and J.J. Pignatello, Model-Aided Characterization of Tenax-TA for Aromatic Compound Uptake from Water, Environ. Toxicol. & Chem., 23: 1592-1599 (2004).
- D. Zhu and J.J. Pignatello, A Concentration-Dependent Multi-Term Linear Free Energy Relationship for Sorption of Organic Compounds to Soils Based on the Hexadecane Dilute-Solution Reference State, Environ. Sci. Technol., 39: 8817-8828 (2005).
- M. Sander, Yuefeng Lu, and J.J. Pignatello, A Thermodynamically Based Index for Quantifying True Sorption Hysteresis, J. Environ. Qual., 34: 1063-1072 (2005).
- Dongqiang Zhu, Seokjoon Kwon, J.J. Pignatello, Adsorption of Single-Ring Organic Compounds to Wood Charcoals Prepared under Different Thermochemical Conditions, Environ. Sci. Technol., 39: 3990-3998 (2005).
- M. Sander and J.J. Pignatello, An Isotope Exchange Technique to Assess Mechanisms of Sorption Hysteresis Applied to Naphthalene in Kerogenous Organic Matter, Environ. Sci. Technol., 39: 7476-7484 (2005).
- M. Sander1, Y. Lu, and J.J. Pignatello, Conditioning Annealing Studies of Natural Organic Matter Solids Linking Irreversible Sorption to Irreversible Structural Expansion, Environ. Sci. Technol., ASAP article (2005).
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Progress 01/01/04 to 12/31/04
Outputs
I. IRREVERSIBLE SORPTION. Sorption of naphthalene (NAPH) and 1,2,4-trichlorobenzene (TCB) to soil humic acid (H-HA), Al3+-crosslinked soil humic acid (Al-HA), and a low-rank coal (Beulah-Zap lignite, BZL) was nonlinear, competitive and hysteretic in all cases. The degree of nonlinearity and the ratio of hole-filling to solid phase dissolution increased in the order of hardness (stiffness) of the solid: H-HA < Al-HA < BZL. Application of a glassy polymer model showed that crosslinking increases the affinity of solutes for the hole relative to the dissolution domain. Solutes show a 15-20 kJ/mole preference for a hole site, attributable to the free energy needed to create a cavity in the dissolution domain to accommodate the solute. Conditioning the sample with chlorobenzene increased sorption and the contribution of hole-filling. The results a) indicate that soil humic acid behaves like a glassy solid; b) metal-ion crosslinking supports a link between nonideal sorption
and glassy character of natural organic matter (NOM); c) underscore the importance of metal ions on humic structure vis a vis sorption; d) are consistent with the pore-deformation mechanism as the underlying cause of sorption irreversibility; and e) emphasize that NOM is not a passive sorbent, but may be physically altered by the sorbate. II. Pi-Pi ELECTRON DONOR-ACCEPTOR INTERACTIONS WITH NOM. The pi-donor compounds, phenanthrene (PHEN), NAPH, and pentamethylbenzene (PMB) form molecular complexes in aqueous and non-aqueous solvents with pi-acceptors, quinones, N-heteroaromatic cations and benzene polycarboxylates chosen to model certain functional subunits of NOM. Complexation was observed by NMR and UV/visible spectroscopies. Sorption of PMB, NAPH and PHEN in a number of soils was found to increase with decreasing pH in the range 2.5 to 7. This behavior was interpreted to be caused by pi-pi interactions with polycarboxy-substituted benzenes and heterocyclic amine subunits whose
acceptor ability increases with decreasing pH. III. BIOAVAILABILITY OF ORGANIC CONTAMINANTS. Equilibrium and diffusion parameters for uptake of benzene, nitrobenzene, NAPH, PHEN, and pyrene by Tenax polymer beads showed general suitability of Tenax for simulating desorption to an infinite sink (complete and rapid uptake) and thus for correlating biological and physical availabilities of chemicals. In another study we determined that metal ion complexing agents (citrate, EDTA, oxalate, pyrophosphate) enhanced desorption of 16 polycyclic aromatic hydrocarbons in coal-tar soil collected from a former manufactured gas plant site; complexing agents appear to act by disrupting humic-metal-mineral linkages and/or by mobilizing colloids. In a study of 15 different soils a correlation was found between the biotransformation-resistant fraction of PHEN (Pseudomonad) and the Tenax desorption-resistant fraction, suggesting that degradation is desorption rate-limited. However, biotransformation of
15 PAH compounds present in the coal-tar soil by indigenous organisms outpaced their chelate-enhanced rates of desorption to Tenax in sterile controls, suggesting that indigenous organisms facilitated desorption.
Impacts
As part of a program to more fully characterize sorption of organic compounds to natural organic matter (NOM) we investigated history-dependent sorption behavior, in particular hysteresis and the conditioning effect, which refers to the enhanced repeat-sorption of a test compound. Our working hypothesis is that these two behaviors are related mechanistically and are due to pore expansion and pore creation processes in the solid that are irreversible on the timescale of molecular diffusion. Such a mechanism is established for glassy organic polymers. The results we observe for sorption of TCB and Naph in the NOM solids are fully consistent with the glassy character of the solids and support the irreversible hole expansion/hole creation mechanism. This advances our understanding of the mechanism of sorption. Pi-pi interactions are possible whenever strongly electron poor and strongly electron rich aromatic or other highly conjugated structures approach in a fact-to-face
orientation. Such structures are common to many pesticides and are present in various components of soil organic matter. Humic substances contain both pi-acceptor and pi-donor subunits. This study has presented the first evidence that pi-pi interactions are likely in these materials. The results of this project are relevant at a fundamental level to agricultural and other activities that result in contact of chemicals with soil. They provide a better understanding of the molecular-level interactions of chemicals with soils.
Publications
- D. Zhu, S. Hyun, J.J. Pignatello, and L.S. Lee, (2004). Evidence for pi-pi Electron Donor-Acceptor Interactions between pi-Donor Aromatic Compounds and pi-Acceptor Sites in Soil Organic Matter, Environ. Sci. Technol., 38: 4361-4368.
- W.J. Braida, J.C. White, and J.J. Pignatello, Indices for Bioavailability and Biotransformation Potential of Contaminants in Soils, Environ. Toxicol. & Chem., 23: 1585-1591 (2004).
- J. Li, J.J. Pignatello, B.F. Smets, D. Grasso, and E. Monserrate, 2005. Bench-scale Evaluation of In Situ Bioremediation Strategies for Soil at a Former Manufactured Gas Plant Site, Environ. Toxicol. Chem., in press.
- Y. Lu and J.J. Pignatello, 2004. History-dependent Sorption in Humic Acids and a Lignite in the Context of a Polymer Model for Natural Organic Matter, Environ. Sci. Technol., 38: 5853-5862.
- Y. Lu and Pignatello, J.J. (2004). Sorption of apolar aromatic compounds to soil humic acid particles affected by aluminum (III) ion crosslinking, J. Environ. Qual., 33: 1314-1321.
- K. Subramaniam, C. Stepp, J.J. Pignatello, B. Smets, and D. Grasso. Enhancement of Polynuclear Aromatic Hydrocarbon Desorption by Complexing Agents in Weathered Soil, Environ. Engineer. Sci. 21: 515-523 (2004).
- H. Wijnja, J.J. Pignatello, and K. Malekani, (2004). Formation of p-p complexes between phenanthrene and model p-acceptor humic subunits. J. Environ. Qual. 33: 265-276.
- D. Zhao and J.J. Pignatello, Model-Aided Characterization of Tenax-TA for Aromatic Compound Uptake from Water, Environ. Toxicol. & Chem., 23: 1592-1599 (2004).
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Progress 01/01/03 to 12/31/03
Outputs
Progress is reported on understanding history-dependent sorption behavior (hysteresis and the "conditioning effect")(Part I) and pi-pi electron donor-acceptor interactions between aromatic compounds and functional groups in soil organic matter (Part II). Part I. To quantify hysteresis, we proposed a universally applicable, free energy-based index which we believe is superior to published empirical indices. Computations on virtual data sets give insight into the thermodynamics of sorption irreversibility. A sensitivity analysis affords recommendations on the setup of sorption/desorption tests. Applied to sorption of 1,4-dichlorobenzene in two soils and a lignite, we find that the TII is independent of solute concentration and solid-to-solution ratio. Irreversible sorption was linked to the glassy character of NOM in a study of hysteresis and the conditioning effect of 1,2,4-trichlorobenzene (TCB) and naphthalene (Naph) in three black-carbon free NOM samples that varied
in glassiness: a soil H+ humic acid (H-HA); Al3+-exchanged form of the same humic acid (Al-HA); and Beulah-Zap lignite (BZL), a low-rank coal. Nonlinearity and hysteresis increased with "hardness" of the NOM (H-HA < Al-HA < BZL). All solids exhibited the conditioning effect when pre-treated with chlorobenzene. Sorption of TCB and Naph in conditioned solids was in each case enhanced, and the isotherm more nonlinear than that of the original solid. The results are consistent with the glassy character of the solids and support the irreversible hole expansion/hole creation mechanism. Part II. Solid-liquid sorption experiments backed by solution phase studies were used to test the hypothesis that pi-pi electron donor-acceptor interactions are important in sorption of relevant xenobiotic chemicals in soil/sediment. The test compounds included donor and acceptor xenobiotics and donor and acceptor compounds used to mimic some of the structural subunits occurring on natural organic matter,
such as ordinary humic substances, kerogens, and black carbon. The test sorbents included soils, prepared charcoals, and graphite. Complexation in solution was established by solubility-enhancement (aqueous solution only); by observing charge-transfer bands in the UV/vis spectrum; and by observing upfield NMR ring-current chemical shifts as a result of the face-to-face orientation of the interacting molecules. Pi-donors naphthalene, phenanthrene, and pentamethylbenzene gave increasing sorption with decreasing pH below neutral in several soils. Presumably this occurs by protonation of aromatic carboxylate groups making them more e- withdrawing. Such enhancement did not occur for non pi-donors. Solution-phase NMR studies with polycarboxy aromatic compounds supported the pi-pi hypothesis. Sorption from water to graphite or a wood charcoal of mono-, di-, and trinitrotoluene increased in that order, and was much stronger in each case than sorption of the corresponding polymethylbenzene of
comparable size, implicating special interaction of the nitroaromatic acceptors with the (donor) polycyclic aromatic surface of the carbon.
Impacts
As part of a program to more fully characterize sorption of organic compounds to natural organic matter (NOM) we investigated history-dependent sorption behavior, in particular hysteresis and the conditioning effect, which refers to the enhanced repeat-sorption of a test compound. Our working hypothesis is that these two behaviors are related mechanistically and are due to pore expansion and pore creation processes in the solid that are irreversible on the timescale of molecular diffusion. Such a mechanism is established for glassy organic polymers. The results we observe for sorption of TCB and Naph in the NOM solids are fully consistent with the glassy character of the solids and support the irreversible hole expansion/hole creation mechanism. This advances our understanding of the mechanism of sorption. Pi-pi interactions are possible whenever strongly electron poor and strongly electron rich aromatic or other highly conjugated structures approach in a fact-to-face
orientation. Such structures are common to many pesticides and are present in various components of soil organic matter. Humic substances contain both pi-acceptor and pi-donor subunits. Chars and soots contain polyaromatic hydrocarbon structures with donor properties. This study has presented the first evidence that pi-pi interactions are likely in these materials. The results of this project are relevant at a fundamental level to agricultural and other activities that result in contact of chemicals with soil. They provide a better understanding of the molecular-level interactions of chemicals with soils.
Publications
- Wijnja, H., Pignatello, J.J. and Malekani, K. 2004. Formation of p-p complexes between phenanthrene and model p-acceptor humic subunits. J. Environ. Qual. 33: 265-276.
- Lu, Y. and Pignatello, J.J. 2004. Sorption of apolar aromatic compounds to soil humic acid particles affected by aluminum (III) ion crosslinking, J. Environ. Qual., in press.
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Progress 01/01/02 to 12/31/02
Outputs
Concentration may play a role in sorption and desorption kinetics. Consistent with theory, fractional mass desorption rates of phenanthrene from each of six soils to infinite dilution increased with initial concentration provided the isotherm was nonlinear. Application of the nonlinear Dual-Mode Diffusion Model (DMDM) gave good fits. The DMDM attributes the increase with concentration of the apparent diffusivity to a decrease in the proportion of sorbate occupying immobile sites (holes) in soil organic matter. The concentration-dependent term correlated with indices that reflect the isotherm linearity. Contaminated sediments often contain mixtures. We studied competitive sorption and desorption of phenanthrene, anthracene and pyrene in an estuarine sediment using the DMDM. Competitive effects in binary or ternary solute systems was well-predicted; compared to the single-solute case sorption was suppressed and the isotherm was more linear. The DMDM applied to the batch
uptake and sequential-batch desorption rate data captured the uptake and release curves. The competitive effect accelerated sorption and desorption, as predicted by theory. Hysteresis (isotherm nonsingularity) is a confounding issue that undermines the assumption of reversibility. We showed that two organic soils, a humic acid, and Al-exchanged humic acid exhibit the 'conditioning effect', which refers to enhancement of sorption following exposure of the sorbent to the same or similar compound. The conditioning effect has been used to support a pore deformation mechanism for hysteresis in glassy polymers. In general, the test solute isotherm in the conditioned soil was shifted upward and was less linear than that in the non-conditioned control. The memory of the conditioning effect persists for > 96 days, but is lost on heating. A three-step (sorption - desorption - re-sorption) experiment proved a link between hysteresis and the conditioning effect. Another study was done to
determine the cause of hysteresis in sorption of benzene to a microporous wood charcoal. Taking care to eliminate artifacts, sorption was highly hysteretic. Sedimentation and volumetric displacement experiments showed pronounced swelling by benzene (up to > 2-fold). Hysteresis is likely due to pore deformation by the solute. Pi-pi interactions of aromatic compounds may contribute to their sorption to humics. Pi-pi complexation occurred between pentamethylbenzene (PMB; model pi donor adsorbate) and 1,3,5-benzenetricarboxylic acid (BTA; pi acceptor and model for humic substances) in water-methanol as shown by upfield chemical shifts. Predictably, the complex is disfavored with volume fraction of methanol and with deprotonation of BTA. In collaboration with Linda Lee's group (Purdue), sorption of various compounds to organic-rich soils was conducted as a function of pH (2-7) to determine if protonation of humic aromatic acid subunits enhances sorption of pi donor compounds. Sorption of
PMB and (especially) PAHs is enhanced with acidification, while sorption of non-donors (polychlorinated biphenyls, dichlorocyclohexane and hexachlorobenzene) is unaffected by pH.
Impacts
The findings are consistent with heterogeneous models of soil organic matter. The finding of concentration-dependent desorption kinetics indicates that concentration should be taken into account in fate models employing kinetic terms. The dual mode diffusion model predicts competitive effects in binary or ternary solute systems. Hysteresis in natural organic matter materials is shown to be due to irreversible pore deformation caused by the presence of the solute. This results in a different pathway of sorption than desorption. The results imply that slow matrix relaxation may contribute (along with molecular diffusion) to often-observed long term desorption resistance. Studies of pi-pi interactions indicate that such interactions are possible in the sorption of strong pi donors like polycyclic aromatic hydrocarbons.
Publications
- Zhao, D., Hunter, M., Pignatello, J. J., and White, J. C. (2002). Application of the Dual-Mode Model for Predicting Competitive Sorption Equilibria and Rates of Polycyclic Aromatic Hydrocarbons in Estuarine Sediment Suspensions. Environ. Toxicol. Chem 21, 2276-2282.
- Lu, Y., and Pignatello, J. J. (2002). Demonstration of the "Conditioning Effect" in Soil Organic Matter in Support of a Pore Deformation Mechanism for Sorption Hysteresis. Environ. Sci. Technol. 36, 4553-4561.
- Braida, W., Lu, Y., Ravikovitch, P. I., Neimark, A. V., and Xing, B. (2002). Sorption Hysteresis of Benzene in Charcoal Particles. Environ. Sci. Technol. 36, 409-417.
- Braida, W., White, J. C., Zhao, D., Ferrandino, F. J., and Pignatello, J. J. (2002). Concentration-Dependent Kinetics of Pollutant Desorption from Soils. Environ. Toxicol. Chem. 21, 2573-2580.
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Progress 01/01/01 to 12/31/01
Outputs
Highly detailed sorption isotherms were used to evaluate a polymer-based model (dual-mode model) for natural organic matter sorption of organic compounds. The model assumes a population of specific adsorption sites ("holes") interspersed uniformly in a dissolution (partition) domain of SOM. The isotherms show linear-scale inflection consistent with the presence of flexible (deformable) porosity as predicted by the glassy polymer-based Extended Dual-Mode Model (EDMM). Sorption of CHCl3 shows time-dependent hysteresis diminished at high concentrations by the plasticizing effect. Sorption of CHCl3 and other compounds also shows a type of hysteresis exhibited by glassy solids known as the conditioning effect in which high loading of sorbate increases hole population upon its removal, and thus leads to enhanced uptake and nonlinearity when sorption is performed a second time or with another solute. The conditioning effect persists for more than 90 days at room temperature
and disappears upon heating at 90 oC. These results implicate a pore deformation mechanism for hysteresis and suggest that slow desorption rates might be, in part, caused by slow relaxation of the organic matter structure. It was shown experimentally by empirical analysis that sorption and desorption rates normalized to the initial concentration increase with initial absolute concentration to the degree the isotherm is nonlinear. These findings indicate that concentration effects should be taken into account in situations where desorption rate is important. A radial dual-mode diffusion model has been developed based on the dual-mode concept. The model assumes Fickian diffusion in the dissolution domain and immobilization in the holes, with microscopic local equilibrium between the two domains. It predicts competitive and concentration effects on sorption and desorption rates Formation of pi-pi complexes was studied in aqueous solvents between the pi-donor, phenanthrene, and various
pi-acceptors that represent structures found in humic materials. These include quinones and N-heterocyclic aromatic cations. pi-pi Compexation was observed and quantified by solubility enhancement, proton-NMR chemical shifts, and UV/visible spectroscopy. The degree of complexation depends on the pi-acceptor strength and the extent of ring overlap between donor and acceptor. Complexation of phenanthrene with the acceptors is not driven primarily by hydrophobic effects. Nevertheless, the polarity of the environment affects pi-pi complexation.
Impacts
The research is designed to help characterize mechanisms by which molecules of pesticides and other toxic organics interact with (adsorb to) soil particles, especially soil organic matter. It is also designed to identify, test and refine models that predict adsorption and desorption rates to and from soil particles.
Publications
- Braida, W. J., White, J. C., Ferrandino, F. J., and Pignatello, J. J. (2001). Effect of solute concentration on sorption of polyaromatic hydrocarbons in soil: uptake rates. Environ. Sci. Technol. 35, 2765-2772.
- Xia, G., and Pignatello, J. J. (2001). Detailed sorption isotherms of polar and apolar compounds in a high-organic soil. Environ. Sci. Technol. 35, 84-94.
- Zhao, D., Pignatello, J. J., White, J. C., Braida, W., and Ferrandino, F. (2001). Dual-mode modeling of competitive and concentration-dependent sorption and desorption kinetics of polycyclic aromatic hydrocarbons in soils. Water Resour. Res. 37, 2205-2212.
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