Progress 10/01/05 to 09/30/10
Outputs
OUTPUTS: We have been studying the impact of black carbon on sorption and bioavailability of natural and contaminant compounds in soil. Black carbon is a natural component of many soils, and biochar, a form of black carbon derived from biomass waste pyrolysis, has been claimed to improve fertility when applied at percent levels in the topsoil. We studied the adsorption of the heavily-used swine antibiotic sulfamethazine (SMZ) and the allelochemicals, cinnamic and coumaric acids, to different commercial biochar prototypes. Little is known about the mechanisms of adsorption of polar and ionizable compounds such as these to black carbon. There is growing concern about the widespread use of antibiotics in animal agriculture. Aromatic and phenolic acids exuded by plant roots play important roles in soil biology and allelopathy. We hypothesized that biochars may enhance sorption and reduce the bioavailability of these compounds in soil. SMZ is hydrophilic (octanol-water partition coefficient, log Kow = 0.27) and exists as a cation, anion, neutral form, or zwitterion (SMZ+, SMZ-, SMZ0, SMZ+/-), depending on pH (pKa, 2.46 and 7.45). Adsorption to biochar alone was highly nonlinear and surprisingly strong. The biochar-water distribution coefficient, Kbc, ranged from 10000 to 10 times greater than literature organic carbon (Koc) values, depending on concentration. Sorption was greatest at about pH 5 where SMZ0 predominates; however, sorption at pH values where SMZ+ and SMZ- predominate was far greater than predicted by their respective Kow values. Depending on its specific surface area, biochar increased the solids-water distribution coefficient of SMZ when added at the 1-2% level to a soil containing 2% OC. Competition experiments shed light on the adsorption mechanism. They showed that neither cation nor anion exchange mechanisms are important. At low pH SMZ+ undergoes pi(+)-pi electron donor-acceptor (EDA) interactions with the graphene surface of black carbon, where the surface acts as a pi-donor and SMZ+ as pi-acceptor by virtue of the e-withdrawing -NH3+ and sulfonamide groups on the anilinium ring. Neutral SMZ0, while driven to the surface mainly by solvophobic forces, may undergo a tautomeric shift to SMZ+/- to take advantage of pi(+)-pi EDA interactions of the anilinium ring. Cinnamic and coumaric acids were studied at pH 6.9 or above where the acids are >99% dissociated. Isotherms in pH 7 buffer were highly nonlinear and give Kbc values up to 104 L/kg, depending on compound (coumarate > cinnamate), concentration, and biochar surface area. Relative to buffered systems, isotherms in unbuffered systems were progressively suppressed as concentration increased, accompanied by an increase in solution pH. After accounting for the buffering capacity of the biochar itself, the stoichiometry was determined to be one mole OH- released per two moles RCO2- adsorbed. Adsorption at constant pH was unaffected by up to 0.1 M Ca or Mg, suggesting no influence of surface charge or metal ion bridging. The driving force for adsorption is proposed to be formation of the conjugate anion, [RCO2H...O2CR]-, which is more solvophobic than the free anion. PARTICIPANTS: Joseph Pignatello, (Connecticut Agricultural Experiment Station). Charisma Lattao, postdoctoral scientist (Connecticut Agricultural Experiment Station). Marc Teixido-Planes, visiting Ph.D. student, (Universitat de Barcelona, Carrer Marti i Franques, 1, 3a Planta, 08028, Barcelona, Spain). Asst. Prof. Jinzhi Ni, visiting scientist (School of Geographical Sciences, Fujian Normal University, Fuzhou, 350007, China). The work performed in 2009 was in partial fulfillment of Objective 1 of W-2082 Multistate Research Project: Objective 1: To identify and quantify fundamental chemical, physical, and biological processes relevant to pesticides and contaminants in agricultural ecosystems. TARGET AUDIENCES: The findings are relevant on a fundamental level to all agricultural stakeholders. Organic compounds (including pesticides, veterinary antibiotics, soil contaminants and natural allelopathic chemicals) are involved in one way or another in virtually all agricultural activities. Sorption is an underlying process in the behavior of all organic compounds in soil and governs their bioavailability to crops as well as to human and ecological receptors. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The affinity of SMZ for black carbon is surprisingly high, considering its hydrophilic nature. We have shown that it is possible to greatly reduce the pore water concentration, thus the mobility and bioavailability, of SMZ in soils by adding biochar at 1-2% levels. This provides extra value to biochar when used as a soil amendment in manure-applied fields, in addition to its purported value as a fertilizer and carbon sink. Sorption of SMZ to black carbon is typically much more nonlinear and many orders of magnitude stronger than sorption to organic carbon, especially at low concentration. However, its strength as a sorbent varies greatly with source material and pyrolysis conditions in its production. The cationic and anionic forms of SMZ appear to have stronger intrinsic affinity for BC than does the neutral molecule after normalizing the distribution coefficient for solvophobic effects by the Kow. Sorption of SMZ+ by organic carbon is thought to involve cation exchange, whereas cation exchange on black carbon appears to be unimportant; instead, the charged site on the molecule engages in pi(+)-pi EDA interaction with the surface. Sorption by OC at neutral pH values where SMZ0 predominates is thought to involve solvophobic forces of the neutral molecule, SMZ0; while the same may occur for black carbon, an additional mechanism may be operative that involves tautomerization to the zwitterion, SMZ+/-, to take advantage of pi(+)-pi EDA interactions. Sorption of SMZ- to OC is considered negligible, whereas sorption of SMZ- to BC is strong and occurs by solvophobic forces. The results on adsorption of cinnamic and coumaric acid anions point to a novel mechanism for adsorption of carboxylic acid anions from water that involves uptake of protons from solution to neutralize the charge and leads to strong adsorption at pHs well above the pKa of the acid in solution. Since humic substances contain abundant aromatic acid moieties, the results also have implications for adsorption of natural organic matter on the surfaces of black carbon and related carbon allotropes such as carbon nanotubes.
Publications
- Sources, Interactions, and Ecological Impacts of Organic Contaminants in Water, Soil, and Sediment: An Introduction to the Special Series, Joseph J. Pignatello, Brian G. Katz, and Hui Li; J. Environ. Qual., 39: 1133-1138 (2010).
- Interactions of Anthropogenic Organic Chemicals with Organic Matter in Natural Particles, J.J. Pignatello, IUPAC SERIES ON BIOPHYSICO-CHEMICAL PROCESSES IN ENVIRONMENTAL SYSTEMS, Volume 3 Biophysico-Chemical Processes of Anthropogenic Organic Compounds in Environmental Systems; B. Xing, N. Senesi and P. M. Huang (eds); Wiley; in press (2011).
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: PART I. Sulfonamide antibiotics introduced to soil through manure application are of concern due to their potential for transmitting antibiotic resistance. Morover, little is known about the sorption of hydrophilic and ionizable compounds, such as the sulfonamides to black carbon, which is a high affinity adsorbent of organic compounds that exists naturally or may be deliberately added to soils in the form of biochar. We focussed on sulfamethazine, 4-amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide (SM; pKa 2.46 and 7.45), sorption to a commercial biochar (BEST Energies Inc.). Biochar--the carbonaceous product of emerging biomass pyrolysis processes--is of interest as a beneficial soil amendment and as a means of large-scale sequestration of carbon. We anticipated that biochar might reduce the bioavailability of SM, hence mitigate its environmental impact. The isotherm at pH 5.2 where the neutral form (SM0) predominates was highly nonlinear (Freundlich exponent of 0.27) corresponding to about a 3 orders-of-magnitude decrease in the observed distribution ratio Kd over the range 0.001 mg/L to 30 mg/L aqueous concentration. Sorption was pH-dependent; fit of the Kd vs pH data to a speciation model gave, for the neutral, cation and anionic forms of the molecule, respectively: log Kd0 = 6.04, log Kd+ = 5.52, and log Kd- = 4.92. Sorption of SM+ was unaffected by up to 0.1 M NH4+. PART II. Solid natural organic matter (NOM) is an aggregate of molecules forming a polymer-like phase. Cross-linking occurs when strands of the same or different molecules are linked by organic or metal ion spacers through covalent or coordination bonds, respectively. Cross-linking creates a more rigid structure and decreases solubility in water. Cross-linking is believed to play an important role in the sorption of organic chemicals by NOM in soil, as shown previously for Al3+-cross-linked humic acid. Cross-linking is also thought to be important in the diagenesis of NOM in soil and sediments. We have successfully crosslinked a soil humic acid (HA) with two different organic spacers: 3,4-epoxycyclohexyl methyl-3',4'-epoxycyclohexane carboxylate (diepoxide) and 1,2,3,4-butanetetracarboxylic acid (BTCA). The spacer was delivered in a volatile solvent either alone (diepoxide case) or together with a coupling catalyst, sodium hypophosphite (BTCA case). After solvent evaporation, the imbibed solid material was heated briefly. Cross-linking was verified spectroscopically in the case of the diepoxide by the progressive disappearance of the characteristic epoxy bands at 789, 798 and 808 cm-1, and a retention of the enhanced signal at 1720 cm-1 for C=O stretching of spacer ester groups. Solubility in water buffered at pH 7 dramatically decrease for both the diepoxy-HA and BTCA-HA compared an HA control subjected to the same procedure but without the spacer or catalyst. The same was true for solubility in polar solvents like pyridine and dimethylsulfoxide. PARTICIPANTS: Joe Pignatello, (Connecticut Agricultural Experiment Station). Tatjana Schneckenburger, visiting PhD student, FB VI Geowissenschaften/Bodenkunde, Campus II - University of Trier, 54286 Trier, Germany. Marc Teixido-Planes, visiting Ph.D. student, UNIVERSITAT DE BARCELONA Carrer Marti i Franques, 1, 3a Planta, 08028 Barcelona (SPAIN). The work performed in 2009 was in partial fulfillment of Objective 1 of W-1082 Multistate Research Project: Objective 1: To identify and quantify fundamental chemical, physical, and biological processes relevant to agricultural pesticides and pharmaceuticals in the environment. TARGET AUDIENCES: The findings are relevant on a fundamental level to all agricultural stakeholders. Organic compounds (including pesticides, soil contaminants and natural allelopathic chemicals) are involved in one way or another in virtually all agricultural activities. Sorption is an underlying process in the behavior of all organic compounds in soil and governs their bioavailability to crops as well as to human and ecological receptors. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
PART I. Sorption of sulfamethazine by the biochar indicates that black carbon can have very high affinity for polar compounds like SM. At a low concentration, the Kd of SM0 for this biochar is almost 6 orders of magnitude greater than the Kow of SM0 (10^0.27) and almost 4 orders of magnitude greater than the mean Koc reported for 5 soils (10^2.11), suggesting that biochar amendment can reduce the bioavailability of SM resulting from swine manure application. The Kd's at low concentration for SM+ and SM- were surprisingly high. Part of the driving force for sorption is the hydrophobic effect--the disruption of the cohesive energy of water upon solvation of apolar parts of molecules. We may use the Kow (which is known individually for SM0, SM+ and SM-) as a surrogate for the component of sorption free energy corresponding to the hydrophobic effect. When the Kd was corrected by Kow, the Kd of SM+ and SM- both were higher than the Kd for SM0 by more than an order of magnitude. The lack of competition for SM+ sites by ammonium ion indicates little or no contribution of cation exchange to SM+ sorption. These are both novel findings which have implications for our understanding of sorption of hydrophilic and ionizable compounds to black carbon. PART II. This is the first report to our knowledge of a successful attempt to covalently cross-link NOM. As expected, cross-linking of humic acid with these two spacers greatly decreases its solubility in water and polar solvents. Differential scanning calorimetry studies are currently underway to determine if cross-linking increases matrix rigidity through an increase in the glass transition temperature. In the near future we will be perfoming experiments to determine if cross-linking affects sorption of organic chemicals.
Publications
- Impact of Biochar Addition to Soil on the Bioavailability of Chemicals Important in Agriculture, J.J. Pignatello, J.C. White and W. Elmer, 2009; Proc. N. Amer. Biochar Conf., Boulder, CO. pp 39-45.
- Bioavailability of contaminants in soil, J.J. Pignatello. In A.J. Singh, et al. (eds.): Advances in Applied Bioremediation, in Soil Biology 17, Series from Springer-Verlag, Heidelberg, Germany, 2009; pp 35-71.
- Effect of Cupric Ion on the Sorption of 2,4,6-Trichlorophenol onto Multi-Walled Carbon Nanotubes. GC Chen, XQ Shan, YS Wang, B Wen, ZG Pei, YN Xie, T Liu and J.J. Pignatello, Water Research 43: 2409-2418 (2009).
- Sorption Irreversibility of 1,4-Dichlorobenzene in Two Natural Organic Matter Rich Geosorbents, M. Sander and J.J. Pignatello, Environ. Toxicol. Chem. 29: 447-457 (2009).
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Hysteresis is a frequently observed phenomenon in sorption experiments that is inconsistent with the key assumption underlying most fate and bioavailability models of sorption reversibility. To elucidate the mechanism of hysteresis in natural organic matter, C-14 isotope tracer exchange was carried out at select points along the isotherms of 1,4-dichlorobenzene (DCB) in a brown coal and a peat soil, holding total DCB concentration constant. Tracer exchange was performed in both the forward (sorption) and reverse (desorption) directions at the bulk sorption points and in the desorption direction at the corresponding bulk desorption points. Bulk DCB isotherms showed concentration-dependent hysteresis. However, the 14C-DCB tracer re-equilibrated in all cases, which was consistent with free exchange between sorbed and aqueous-phase molecules. These results rule out common experimental artifacts and demonstrate that sorption of bulk DCB to these carbonaceous sorbents is truly hysteretic (i.e., irreversible). Solid-phase extraction of equilibrated DCB with an infinite sink polymer, Tenax revealed a small highly desorption-resistant fraction. PARTICIPANTS: J.J. Pignatello, PD. Conceived, designed, obtained funding for, oversaw progress on project, helped write manuscript, and presented results at meetings. M. Sander. Yale Ph.D. student who carried out laboratory experiments, helped design experiments, helped write manuscript, and presented results at meetings. TARGET AUDIENCES: Being of a fundamental nature, this research targeted the scientific community. The results will assist scientists in modeling and predicting the fate and bioavailability of chemicals in soil, groundwater and sediment. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The differences in rates between bulk and tracer sorption and desorption are consistent with the coupling of bulk DCB diffusion to another process that retards equilibration. We assign this process to matrix swelling and shrinking by sorbing and desorbing molecules. The hysteresis is attributed to inelastic expansion during the swelling/shrinking cycle that results in creation of additional void space in the matrix, which enhances affinity for sorbate molecules in the desorption step. Comparing the present results to previous results for naphthalene (NAPH), we find that irreversible effects are similar for DCB and NAPH in the coal, but differ for DCB between the coal and the peat. An explanation based on physical properties differences of these sorbents is provided. The highly desorption-resistant fraction, while too small to account for the observed hysteresis, may represent molecules that have become trapped as the matrix collapses and stiffens during abrupt desorption in the presence of Tenax. The results confirm and broaden our previous findings that sorption hysteresis in natural organic matter can be due to the creation of long-lifetime metastable states that arise in response to sorbate loading. We have shown that "irreversible" effects are similar for nonpolar aromatic molecules of comparable size; that they depend on concentration; and that this concentration dependence depends on sorbent properties. The results have important implications for modeling solute transport and bioavailability of pollutants in the environment because existing models are based on sorption reversibility. The finding that matrix deformation influences uptake and release rates suggests that relaxation kinetics may have to be considered in solute transport models.
Publications
- 1. Sander, M. and Pignatello, J.J. 2009. Sorption Irreversibility of 1,4-Dichlorobenzene in Two Natural Organic Matter Rich Geosorbents. Environmental Toxicology and Chemistry (in press).
- 2. Sander, M. and Pignatello, J.J. 2008. Sorption Irreversibility of Hydrophobic Compounds in NOM Solids is Due to Inelastic Matrix Flexing, Session on Long-Term and Non-Extractable Residue Formation of Organic Pollutants in Soils and Sediments; SETAC Europe Annual Meeting; Warsaw, Poland; May 24-30.
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: Sorption in soils and sediments is generally modeled as a reversible process. However, sorption hysteresis is a commonly observed phenomenon that, if due to real causes and not experimental artifacts, has important implications for the mobility and bioavailability of anthropogenic chemicals. We examined the reversibility of sorption by wood char from water of benzene, toluene, and nitrobenzene, both singly and in pairs. The char was prepared at 400 oC for two hours under limited oxygen availability. A previous study showed that the three compounds compete for the same set of adsorption sites on the char [Sander and Pignatello Environ. Sci. Technol. 2005, 39, 1606-1615]. Artificial causes of hysteresis such as slow diffusion and mass loss were ruled out in controls. Single-solute sorption was weakly hysteretic at high concentrations and approximately the same for the three adsorbates; this finding is taken as evidence that hysteresis is true and supports irreversible pore
deformation by the incoming adsorbate as the cause, as demonstrated in previous studies for natural organic matter. Sorption in bisolute systems was weakly hysteretic at low co-solute concentration but became more and more hysteretic as the co-solute concentration increased. We attribute the growing hysteresis to the Competitor Dilution Effect--a heretofore-unrecognized thermodynamic cause of hysteresis that operates when a competing chemical species is simultaneously diluted along with the target species in the desorption step. This mechanism operates because the target species re-equilibrates from a point on the sorption branch of the isotherm where competition is relatively high, to a point on the desorption branch where competition is relatively low owing to the changing competitor concentration. The competitor also caused an increase in the linearity of the target solute isotherm, which can also be attributed to competition thermodynamics. Simulations using a thermodynamic
competition model, Ideal Adsorbed Solution Theory, support the hypothesis.
PARTICIPANTS: Joseph J. Pignatello is the principal investigator. Michael Sander is a student from Yale University who assisted on the project.
TARGET AUDIENCES: The findings are relevant on a fundamental level to all agricultural stakeholders. Organic compounds (including pesticides, soil contaminants and natural allelopathic chemicals) are involved in one way or another in virtually all agricultural activities. The findings also impact scientific community in the general field of sorption, an underlying process in the behavior of all organic compounds in soil.
Impacts
This study demonstrates an artificial cause of hysteresis that has real implications for chemical availability in the environment. The Competitor Dilution Effect applies to both solution-solid and gas-solid sorption. It is expected to play a role in pollutant behavior in real systems when competing substances, either natural or anthropogenic, are diluted or degraded. It would leave the target pollutant less accessible with time. The results also show that competing substances may affect the linearity of the target species isotherm.
Publications
- Sander, M. and J.J. Pignatello, On the Reversibility of Sorption to Black Carbon: Distinguishing True Hysteresis from Artificial Hysteresis Caused by Dilution of a Competing Adsorbate, Environ. Sci. Technol., 41: 843-849 (2007).
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Progress 01/01/06 to 12/31/06
Outputs
Our efforts in this period focused on sorption irreversibility and the effects of natural organic matter on sorption to environmental black carbon (BC, in the form of charred biomass). Although sorption reversibility is usually assumed in fate and transport models, many compounds show hysteresis and a related phenomenon known as the conditioning effect. Using polychlorinated benzenes, we observed the conditioning effect (enhancement in the sorption distribution coefficient upon resorption) for a peat soil, a soil humic acid, and a glassy polymer, poly(vinylchloride), but not for a rubbery polymer, poly(ethylene). The conditioning effect relaxed upon annealing the sample between 45 oC and 91 oC in a manner similar to the relaxation of free volume and enthalpy of glassy polymers. BC plays a potentially important role in the availability of pollutants in soils and sediments. Recent indirect evidence points to the possible attenuation of the high surface activity of raw
BC by natural substances. Simulated "aging" of prepared wood char particles in a soil-water suspension lead to a strong decline in char surface area (TSA) by N2 adsorption at 77 K with BET analysis and a more modest decline in affinity for dissolved benzene. In order to determine the cause of this reduction in surface activity, we studied the effects of soil humic acid (HA), fulvic acid (FA) and triglycerides in a commercial vegetable oil representing humic lipids on the surface properties and affinity for organic compounds of synthesized wood charcoal. N2-TSA was suppressed by up to two orders of magnitude with increased lipid loading, while CO2 cumulative surface area up to 1.4 nm (at 273K) and benzene adsorption (at 293K) were hardly affected. Char powder suspended in a solution of HA or FA was loaded with HA or FA via adsorption, evaporation of the water or co-flocculation with Al3+. Such treatments were chosen to simulate initial and more advanced stages of environmental
exposure. Co-evaporation dramatically reduced N2 TSA of the char, but only moderately reduced the CO2 CSA. Organic compound adsorption was suppressed in proportion to molecular size: benzene < naphthalene < phenanthrene, and 1,2,4-trichlorobenzene << phenanthrene, for humics in the adsorbed and co-flocculated states, respectively. HA also increased isotherm linearity. Our proposed model assumes humic substances are restricted to the external surface or extending part way into pore throats, where they act as pore blocking or competitive agents, depending on temperature and molecular size of the adsorbate. Nitrogen is blocked from internal porespace due to the stiffness of humic strands at 77 K, resulting in artificially low surface area. At higher temperatures (CO2, 273 K; organics, 293 K), humic strands are more flexible, allowing access to interior pores. The counter-intuitive molecular size dependence of adsorption suppression by humics is due a molecular sieving effect in pores in
which the adsorption space available to the organic compound is more and more restricted to external sites.
Impacts
Sorption to soil particles is an underlying process in the fate, transport and bioavailability of chemicals in soil. The findings pertaining to the conditioning effect provide compelling evidence for the glassy, non-equilibrium nature of natural organic matter solids and for irreversible structural expansion as a cause of irreversible sorption. The findings on the effects of humic substances on adsorption to charcoal indicate that N2 is an unsuitable probe for microporosity in black carbon (BC) and natural organic matter in geosorbents. They also show that adsorption of organic compounds to BC may be attenuated by exposure to humic substances in soil over time. All of these findings improve our understanding of and ability to predict sorption of organic compounds in soils.
Publications
- Conditioning Annealing Studies of Natural Organic Matter Solids Linking Irreversible Sorption to Irreversible Structural Expansion, M. Sander1, Y. Lu, and J.J. Pignatello, Environ. Sci. Technol., 40: 170-178 (2006). [Correction, 40: 6518 (2006)]
- Nonlinear and competitive sorption of apolar compounds in black carbon-free natural organic materials, J.J. Pignatello, Y. Lu, E.J. LeBoeuf, W. Huang, J. Song and B. Xing J. Environ. Qual., 35: 1049-1059 (2006)
- Effect of Natural Organic Substances on the Surface and Adsorptive Properties of Environmental Black Carbon (char): Attenuation of Surface Activity by Humic and Fulvic Acids, J. J. Pignatello, S. Kwon, and Y. Lu, Environ. Sci. Technol., 40: 7757-7763 (2006).
- 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. S. Kwon and J.J. Pignatello, Environ. Sci. Technol., 39: 7932-7939 (2005).
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