Grantee Research Project Results
1999 Progress Report: The Influence of Nanoporosity in Soils from Contaminated Sites on Hydrocarbon Desorption Kinetics and Bioavailability
EPA Grant Number: R825959Title: The Influence of Nanoporosity in Soils from Contaminated Sites on Hydrocarbon Desorption Kinetics and Bioavailability
Investigators: Pignatello, Joseph J. , Neimark, Alexander V.
Institution: Connecticut Agricultural Experiment Station , Tri / Princeton
EPA Project Officer: Aja, Hayley
Project Period: January 1, 1998 through December 31, 2000
Project Period Covered by this Report: January 1, 1999 through December 31, 2000
Project Amount: $436,399
RFA: EPA/DOE/NSF/ONR - Joint Program On Bioremediation (1997) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
The primary focus of this research is to obtain a better understanding of the link between desorption and bioavailability. The objectives of this project are to: (1) develop a methodology to characterize the nanoporosity of a number of soils and aquifer sediments of current interest based on carbon dioxide adsorption; and (2) determine the relationship, if any, between nanoporosity and certain physical-chemical and biological availability parameters for mono- and polycyclic aromatic hydrocarbon contaminants. The latter objective includes determining the influence of soil alteration and sorption competitive effects on bioavailability.Progress Summary:
Studies in the second year focused on: (1) developing protocol and molecular level theoretical models for assessing nanoporosity in soil specimens using experimental gas adsorption isotherms and molecular models; and (2) correlating desorption rates and bioavailability for polycyclic aromatic hydrocarbons, including assessing the effects of competitive sorption on sorption equilibria, sorption/desorption rates, and bioavailability.
Characterizing Nanoporosity. We have developed and verified a new experimental protocol and molecular level theoretical models for assessing nanoporosity and soil retention ability by using carbon dioxide as a molecular probe. We observe sorption-desorption hysteresis of CO2 associated primarily with sorption to materials with high organic carbon content (i.e., soil organic matter) and its humic acid and humin fractions. We hypothesize that strong retention and sequestration of various organic molecules and sorption hysteresis of carbon dioxide are caused by similar mechanisms. Therefore, carbon dioxide can be used as a suitable molecular probe to study structural and sorption-desorption properties of soil particles containing soil organic matter (SOM). The CO2 adsorption-desorption hysteresis presumably indicates irreversibility of sorption in SOM nanopores. A new measure of irreversibility has been introduced to quantify the degree of hysteresis. This quantity can be related to soil retention ability. A new set of intermolecular parameters for CO2/solid potentials was defined and verified against literature data. The Monte Carlo (MC) and Density Functional Theory (DFT) simulation models have been developed and verified against reference samples. Preliminary results demonstrate consistency of the results of DFT and MC based models. The micropore size distributions are calculated from comparison of the experimental gas adsorption isotherms and the theoretical isotherms in model pores predicted by means of DFT and grand canonical MC simulations. The CO2 adsorption isotherms at 0oC and N2 adsorption isotherms at 77oK on 20+ soils samples and reference sorbents were measured and the pore size distributions were constructed.
Correlating Desorption and Bioavailability. A series of parallel desorption and biodegradation experiments were carried out on radiolabeled phenanthrene, which had been equilibrated for a period of 180 days with 7 different soils of organic carbon content in the range 0.18 percent to 43.9 percent (Mount Pleasant silt loam, Pahokee peat soil, Wurtsmith AFB 1A Bottom, Cheshire fine sandy loam, Port Hueneme, Seal Beach, and modified Seal Beach). Desorption rates were measured using Tenax? as an infinite sink for phenanthrene. In general, the experimental results show an initial fast rate of desorption that significantly decreases after 30 days. The desorption rate is concentration dependent: the higher the initial sorbed concentration, the greater the initial rate of desorption. Desorption profiles also suggest the presence of a large fraction of phenanthrene that is highly resistant to desorption. This fraction ranges between 15 and 65 percent of the total amount of phenanthrene initially sorbed. Biodegradation experiments were run using Pseudomonas strain R grown up on phenanthrene. Mineralization rates follow a similar trend as the desorption rates. To characterize the bioavailability of sorbed phenanthrene to biodegraders, two dimensionless indexes are proposed. The biodegradation potential index (BP) is the ratio of moles of phenanthrene biodegraded after 30 days of inoculation of Pseudomonas strain R to moles of phenanthrene remaining sorbed after 30 days of desorption to an infinite sink (Tenax?). This index provides an estimate of the maximum amount of biodegradation that may be achieved by a given system in a given period of time, assuming that desorption is prerequisite to degradation. The bioavailability index (BA) estimates the ratio between the extent of biodegradation and the maximum extent of sorption and is defined as the ratio of moles of phenanthrene biodegraded to moles of phenanthrene desorbed after 30 days of inoculation of Pseudomonas strain R and desorption to an infinite sink, respectively. One advantage of the proposed indexes is that they do not require the assumption of any particular mechanism and, by combining data from desorption and biodegradation studies performed in a similar fashion, they emphasize the differences between the degradation and desorption behavior of sorbed phenanthrene. Preliminary results suggest that biodegradation may be limited by the rate of desorption. However, Pseudomonas strain R cannot keep up with the maximum rate of desorption of phenanthrene as measured by the infinite sink method.
Future Activities:
The hysteresis phenomenon requires further study. We currently are developing molecular models of sorption hysteresis that can be tested against capillary condensation isotherms collected on reference adsorbents such as mesoporous molecular sieves. The bioavailability experiments are still in progress. By the end of the year, we will have collected all the data and then will have an opportunity to evaluate the relation among bioavailability, hysteresis, and nanoporosity.Journal Articles on this Report : 6 Displayed | Download in RIS Format
Other project views: | All 61 publications | 19 publications in selected types | All 19 journal articles |
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Type | Citation | ||
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Neimark AV, Ravikovitch PI, Vishnyakov A. Adsorption hysteresis in nanopores. Physical Review E 2000, Volume: 62 , Number: 2,A (AUG) , Page: R1493-R1496. |
R825959 (1999) R825959 (Final) |
not available |
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Ravikovitch PI, Vishnyakov A, Russo R, Neimark AV. Unified approach to pore size characterization of microporous carbonaceous materials from nitrogen, argon and carbon dioxide adsorption isotherms. Langmuir 2000;16(5):2311-2320. |
R825959 (1999) R825959 (Final) |
not available |
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Vishnyakov A, Ravikovitch PI, Neimark, AV. Molecular level models for CO2 sorption in nanopores. Langmuir 1999;15:8736-8742. |
R825959 (1998) R825959 (1999) R825959 (Final) |
Exit Exit |
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White JC, Hunter M, Pignatello JJ, Nam KP, Alexander M. Correlation between the biological and physical availabilities of phenanthrene in soils and soil humin in aging experiments. Environmental Toxicology Chemistry 1999;18(8):1720-1727. |
R825959 (1998) R825959 (1999) R825959 (Final) |
not available |
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White JC, Hunter M, Pignatello JJ, Alexander M. Increase in the bioavailability of aged phenanthrene in soils by competitive displacement with pyrene. Environmental Toxicology and Chemistry 1999;18(8):1728-1732. |
R825959 (1998) R825959 (1999) R825959 (Final) |
not available |
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White JC, Pignatello JJ. Influence of bisolute competition on the desorption kinetics of polycyclic aromatic hydrocarbons in soil. Environmental Science & Technology 1999;33(23):4294-4298. |
R825959 (1998) R825959 (1999) R825959 (Final) |
not available |
Supplemental Keywords:
adsorption, absorption, groundwater, soil, sediments, bioavailability, bioremediation, environmental chemistry, environmental microbiology, modeling., Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Environmental Chemistry, Geochemistry, Contaminated Sediments, Chemistry, Environmental Microbiology, Microbiology, Bioremediation, Environmental Engineering, Geology, sorption, Toluene, contaminated sites, density functional theory, contaminated sediment, aquifer sediments, sorption kinetics, PAH, soil characterization, bioremediation of soils, sediments, nonoporosity, hydrocarbon desorption kinetics, PhenanthreneProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.