Grantee Research Project Results
1999 Progress Report: Determination of Binding Interactions Between Xenobiotic Chemicals and Soil
EPA Grant Number: R826646Title: Determination of Binding Interactions Between Xenobiotic Chemicals and Soil
Investigators: Bollag, Jean-Marc , Dec, Jerzy
Institution: Pennsylvania State University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $408,775
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Sustainable and Healthy Communities , Land and Waste Management , Air , Safer Chemicals
Objective:
Immobilization processes in soil are of great environmental importance because they may lead to a considerable reduction in the bioavailability and degradation of organic pollutants. The purpose of this project is to evaluate the mechanisms of pollutant immobilization in soil using 2,4,6-trinitrotoluene (TNT), anthracene, and 2,4-dichlorophenol (DCP) as model contaminants. The project integrates several experimental approaches that, in recent years, have shown great potential for investigating soil-bound chemicals. The compounds under investigation are labeled with 14C and 13C or 15N for analysis by radiocounting, and 13C or 15N nuclear magnetic resonance (NMR) spectroscopy. In this project period, the research focused on two topics: (1) the use of NMR to evaluate the nature of bonds formed after incubating 15N-labeled TNT in soil under anaerobic and aerobic conditions; and (2) the evaluation of sorption and sequestration mechanisms based on batch equilibrium isotherms determined after either short or long contact times between DCP and different soils.Progress Summary:
Soil used for NMR studies was obtained from a former TNT production site. Prior to incubation, it was spiked with 4.0 g [15N3]TNT per kg (dry weight) and [14C]TNT (5.0 x 106 Bq). The incubation was carried out in the reactor containing 1.2 L of 50 mM sodium/potassium phosphate buffer (pH = 7.3) at 30?C; the soil was amended with a mixed bacterial culture, mineral salts, and glucose (10 mM). The anaerobic phase (51 days) was followed by an aerobic phase of 32 days. The high performance liquid chromatography (HPLC) and NMR analyses of the liquid phase and methanol extracts indicated that during the anaerobic phase, TNT was gradually reduced to hydroxylaminodinitrotoluenes, isomeric aminodinitrotoluenes, and 2,4-diaminonitrotoluene in decreasing amounts with time. After 42 days of anaerobic treatment, neither TNT nor its metabolites could be extracted from the soil. All NMR spectra of fulvic acids showed the presence of a peak at 24 ppm for a protonated amino group. The 15N NMR spectra of the humic acid fraction for different incubation periods showed that initial binding occurred via ionic interactions of azoxy compounds (300?310 ppm). Nitro groups (374 ppm) also were observed. With time, there was a dramatic reduction of the nitro peaks and an increase in the intensity of the peak corresponding to bound aromatic amines (58 ppm). Also, the azoxy signals (300 ppm) disappeared with time. During the aerobic treatment, there was an increase in the amount of amino groups (51 ppm) and amides (121 ppm). The NMR linewidths suggest strong (covalent) binding interactions between the metabolites and humic acid.The spectrum of silylated humin after 25 days showed a large peak at about 360?380 ppm that corresponded to the nitro region, and another resonance centered at 310 ppm, which was representative of azoxy species. The nitro group also was shown in the spectrum for 51 days (aerobic phase), with additional resonances at 35 and 120?170 ppm, corresponding to bound aliphatic amines, hydroxylamines, substituted amines, and amides (120?160 ppm). The aerobic phase (51?83 days) caused a significant reduction of the aliphatic amine moiety. The resonances in the region between 270?320 ppm corresponded to bound imines. Bound chemicals retained nitro functionalities (372?376 ppm). The NMR spectrum of silylated humin control showed no resonances. Based on the NMR spectra, pathways for binding of TNT or its dimers to humin were proposed. The spectrum for the silylated whole soil after 83 days of incubation was representative of the collective features observed for fulvic acid, humic acid, and silylated humin.
Batch equilibrium experiments with DCP were carried out using three different soils. At early contact times, the rate of DCP adsorption increased slightly with time (0?3 hours) and began to decrease and level off at about 5 hours. The Kf and N values at this period did not differ considerably from those at 8 hours and were representative of partitioning (0?3 hours) and sorption phenomena (3?8 hours). As indicated by Kf values, the adsorption of DCP under sterile conditions ranged between Kf = 0.014 for 8 hours and 3.76 for 14 days, depending on the incubation time (8 hours to 14 days) and the type of soil. The Kf values indicated that the adsorption of DCP in soils 1 and 3 increased with time rather quickly; however, judging by the changes in N values (linearity), there was little sequestration. The linearity of adsorption isotherms for soil 1 (under sterile conditions) fluctuated slightly with time, but practically did not change between 8 hours and 14 days (0.873 and 0.851, respectively), indicating that sequestration had not yet started. The strong fluctuation of N and Kf values for soil 2 (0.513?1.140) may be indicative of sequestration phenomena overlapping with adsorption. The N values for soil 3 showed less fluctuation (0.833?1.29) and, like those for soil 1, did not appear to indicate the beginning of sequestration. The N values for nonsterile soils were decreasing with time much faster than those for sterile soils, indicating the involvement of microbial processes. Also, the increases in the adsorption coefficient (Kf) for nonsterile soils were much faster than those for sterile soils, confirming the involvement of microorganisms.
Future Activities:
Future work on this project will include an additional pollutant, anthracene. The research with TNT will focus mostly on the batch equilibrium experiments, as in the current project period TNT was used only in the 15N NMR studies. The batch equilibrium experiments for DCP will continue to cover all contact times up to 2.5 years. Simultaneously, 13C-labeled DCP will be monitored by 13C NMR as it undergoes sequestration and binding over the 2.5-year incubation in nonsterile soil. Research with anthracene will focus first on batch equilibrium experiments, but soon also will include incubation experiments with the 13C-labeled compound for analysis by 13C NMR. The methanol- and NaOH-extracted soil samples generated in all experiments are stored in the freezer for tests on the bioavailability of bound chemicals that will be conducted in an anaerobic respirometer system.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 5 publications | 5 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Achtnich C, Fernandes E, Bollag JM, Knackmuss HJ, Lenke H. Covalent binding of reduced metabolites of [N-15(3)]TNT to soil organic matter during a bioremediation process analyzed by N-15 NMR spectroscopy. Environmental Science & Technology 1999;33(24):4448-4456. |
R826646 (1999) |
not available |
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Dec J, Bollag J-M. Phenoloxidase-mediated interactions of phenols and anilines with humic materials. Journal of Environmental Quality 2000;29(3):665-676. |
R826646 (1999) R826646 (Final) R823847 (Final) |
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Supplemental Keywords:
xenobiotics, environmental chemistry, terrestrial systems, cleanup, risk assessment, humification, bioremediation, detoxification, microbial transformation, metabolism, analytical methods, agriculture, industry., RFA, Scientific Discipline, Toxics, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Environmental Chemistry, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Contaminated Sediments, Remediation, pesticides, Ecological Effects - Environmental Exposure & Risk, Fate & Transport, Ecological Risk Assessment, sediment treatment, degradation of organic pollutants, fate and transport, risk assessment, hydrocarbon, xenobiotics, contaminant transport, sediment transport, sorbed contaminants, contaminated sediment, chemical contaminants, PAH, chemical transport, chemical kinetics, ecological assessment, assessment methodsRelevant Websites:
http://www.cos.com/Progress 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.