Grantee Research Project Results
Final Report: A Comprehensive Investigation of the Effects of Organic Geochemistry on the Sorption-Desorption, Sequestration, and Bioavailability of Mixed Organic Contaminants in Subsurface Systems
EPA Grant Number: R825962Title: A Comprehensive Investigation of the Effects of Organic Geochemistry on the Sorption-Desorption, Sequestration, and Bioavailability of Mixed Organic Contaminants in Subsurface Systems
Investigators: Weber, Walter J.
Institution: University of Michigan
EPA Project Officer: Aja, Hayley
Project Period: January 1, 1998 through December 31, 2000
Project Amount: $440,748
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 fundamental objective of this study was to establish a rigorous scientific foundation for risk-based decisions regarding acceptable alternative endpoints for soil and sediment remediation. The study evaluated the complex role of soil and sediment organic geochemistry on the environmental mobility and bioavailability of hydrophobic organic contaminants (HOCs) in systems with multiple organic solutes. Particular emphasis was placed on examination and documentation of the multiple mechanisms that slow desorption and contaminant sequestration. To this end, systematic studies were conducted in multi-contaminant systems to address the effect of soil organic matter on: (1) HOC sorption-desorption hysteresis, desorption rates, and sequestration; (2) the subcritical water extractability of sorbed HOCs; (3) the bioavailability of sorbed HOCs to bacteria and to earthworms; and (4) the effect of cumulative solute residence time on the sorbent or so-called "aging" on each of the foregoing.Summary/Accomplishments (Outputs/Outcomes):
Effects of Soil Organic Matter on Phenanthrene Desorption Rates and Bioavailability. Sorption properties and biological mineralization rates of phenanthrene with respect to three selected geosorbents with different types of soil organic matter (SOM) were evaluated. The chemical nature of the organic matter associated with each geosorbent was characterized using solid-state 13C-NMR spectrometry. Mineralization profiles revealed that initial degradation rates are much faster for the two geosorbents comprised of diagenetically younger peat and humic type SOM, Michigan peat and Chelsea soil, than for the third geosorbent containing primarily older kerogen SOM, Lachine shale. Phenanthrene mineralization in both Michigan Peat and Chelsea soil nearly ceased after the initial fast desorption period, whereas mineralization in the Lachine shale system continued at a nearly constant rate. Abiotic desorption experiments using an infinite-sink experimental method revealed trends similar to those observed in the mineralization experiments in shale systems, suggesting that desorption was the rate-limiting step for biodegradation in that system. Interestingly, no significant differences between two different aging periods of two and four months were found in these experiments. After completion of the mineralization experiments, both combustion and methanol soxhlet extraction were used to recover 14C-organics from the geosorbents. The amount of extractable 14C-organic material varied with the degree of diagenetic alteration of the soil; relatively small amounts of 14C-organics were extracted from the younger peat and humic type SOM while virtually all 14C-organics were extracted from the older kerogen type SOM. The extraction and mineralization results suggest that polycyclic aromatic hydrocarbons (PAHs) biotransformation may change the nature of sequestration. Chemical reactions, such as oxidative coupling, may become predominant in some systems. Coupling of hydroxylated phenanthrene metabolites with reactive components of the SOM would result in very low bioavailability and high non-extractabiliy, as observed in the geosorbents containing younger SOMs. Peat and humic type SOMs are comprised of more oxidized reactive groups, and are more likely to be involved in coupling reactions. The results of these studies revealed that both the desorption behavior and the microbial bioavailability of the sorbed contaminant are markedly influenced by the physicochemical character of the organic matter.
Modeling the Rates of Phenanthrene Desorption from Geosorbents. Rates and extents of phenanthrene desorption were studied for more than 250 days as functions of sorbent type, initial loading level, and aging. Apparent first-order desorption rate constants for the slowly desorbing fraction were found to: (1) range from 0.00086 to 0.148 days-1 for geosorbents that contain geologically mature kerogen and less rigid humic-type soil organic matter, respectively; (2) decrease by as much as an order of magnitude with decreased initial sorbed solid-phase phenanthrene concentration; (3) decrease by a factor of two with increased aging time for a humic topsoil but remain unaffected by aging times beyond three months for a shale; and (4) be 1-2 orders of magnitude lower than rate constants for the rapidly desorbing phenanthrene fractions for any given contaminated sample. Six models were used to fit desorption rate data. Biphasic diffusion and biphasic first-order models with three fitting parameters had the greatest utility, and are potentially useful in a variety of environmental applications. A 5-parameter triphasic first-order desorption model, a 2-parameter gamma-function model, and a 1- or 2-parameter pore diffusion model were less useful.
Effects of Chlorinated Solvents on the Sorption and Desorption Behavior of Phenanthrene. Experiments were conducted to investigate the displacement of PAHs sorbed onto geosorbents by aliphatic and aromatic compounds likely to occur as co-solutes in contaminated sites. Phenanthrene was chosen as the model PAH compound and trichloroethylene (TCE) and dichlorobenzene (DCB) as the co-solutes. Phenanthrene sorption in the presence of TCE and DCB increased and the isotherms were more linear than those of only phenanthrene. This results from swelling of the soil matrix, an effect that increases the sorption capacity of the soil organic matter for the primary solute, phenanthrene. Competition was observed for phenanthrene sorption in the presence of DCB at low phenanthrene concentrations. In desorption experiments, some phenanthrene was entrapped at equilibrium, which suggests that abrupt collapses of the SOM cause phenanthrene to be sequestered in soil matrices. The displacement experiments indicate that TCE does not displace sorbed phenanthrene. However, phenanthrene is displaced by DCB at low phenanthrene concentrations, and this result is consistent with that of phenanthrene sorption in the presence of DCB.
Predicting Long-Term Desorption Kinetics of Sequestered HOCs by Subcritical Water Extraction. Subcritical water extraction was developed as a technique for rapidly predicting the long-term phenanthrene desorption behavior from contaminated soils or sediments. It is expected that this technique will be invaluable for engineers and scientists planning remediation schemes and/or grappling with difficult alternative remediation endpoint decisions. Liquid-phase temperature programmed desorption (TPD) experiments determined the apparent activation energies of phenanthrene desorption from contaminated soils and sediments. Apparent desorption activation energies also were measured by Arrhenius modeling of isothermal desorption rates at temperatures between 25°C and 150°C. The slow release rates of desorption resistant phenanthrene fractions at 25°C, which were measured for up to 455 days, correlated with apparent desorption activation energies, which ranged from 30 to 80 kJ/mol, depending on sediment type and contamination level. Furthermore, isothermal phenanthrene desorption profiles at elevated temperatures matched those at 25°C, but time scales were reduced by several orders of magnitude. Time scaling factors to match 25°C desorption profiles to desorption at elevated temperatures were calculated readily from apparent activation energies. The current research reveals that superheated water desorption experiments can rapidly predict both rates and extents of long-term phenanthrene desorption. This development is of great practical value because ambient desorption experiments can take years to measure, while superheated water extractions and TPDs are accomplished in only a few hours.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 13 publications | 3 publications in selected types | All 3 journal articles |
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Johnson MD, Keinath TM 2nd, Weber Jr WJ. A distributed reactivity model for sorption by soils and sediments. 14. Characterization and modeling of phenanthrene desorption rates. Environmental Science & Technology 2001;35(8):1688-1695. |
R825962 (Final) R828246 (2002) |
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Johnson MD, Weber Jr WJ. Rapid prediction of long-term rates of contaminant desorption from soils and sediments. Environmental Science & Technology 2001;35(2):427-433. |
R825962 (Final) R828246 (2002) |
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Lueking AD, Huang W, Soderstrom-Schwarz S, Kim M, Weber WJ. Relationship of soil organic matter characteristics to organic contaminant sequestration and bioavailability. Journal of Environmental Quality 2000;29(1):317-323. |
R825962 (Final) |
Exit Exit |
Supplemental Keywords:
cleanup, restoration, chemical transport, environmental chemistry, geochemistry, environmental engineering, contaminant mobility, alternative remediation endpoints, biotransformation of contaminants, subsurface systems, contaminant transport, natural attenuation., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Contaminated Sediments, Ecosystem/Assessment/Indicators, Ecosystem Protection, exploratory research environmental biology, Chemical Mixtures - Environmental Exposure & Risk, Environmental Chemistry, Health Risk Assessment, Chemistry, Ecological Effects - Environmental Exposure & Risk, chemical mixtures, Bioremediation, Biology, Environmental Engineering, Geology, risk assessment, fate and transport, risk-based decisions, contaminated sediment, chemical transport, subsurface systems, mixed organic contaminants, geochemistry, soil characterization, contaminant release, hydrocarbons, exposure assessment, chlorinated solvents, hydrophobic organic contaminantsProgress 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.