Grantee Research Project Results
1999 Progress Report: Microbial Community Dynamics of PCB Dechlorination in Sediments
EPA Grant Number: R825449Title: Microbial Community Dynamics of PCB Dechlorination in Sediments
Investigators: Rhee, G-Yull
Institution: New York State Department of Health
Current Institution: The State University of New York
EPA Project Officer: Chung, Serena
Project Period: January 1, 1997 through December 31, 1999 (Extended to December 31, 2000)
Project Period Covered by this Report: January 1, 1999 through December 31, 2000
Project Amount: $508,964
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:
The objectives of this project are to determine: (1) the dynamics and structure of the dechlorinating microbial community in defined functional and phylogenic groups (including the dechlorinating population, methanogens, sulfidogens, and spore formers) during the course of dechlorination; (2) the kinetics of dechlorination based on population-normalized rates. Because polychlorinated biphenyl (PCB) dechlorination is very slow, taking place over months, and the population size of dechlorinating organisms and community composition also may vary with PCB concentration, it is necessary to determine the rate normalized with the size of the dechlorinating population to understand true kinetics; and (3) in situ dechlorination potential in natural sediments. Based on the kinetic data and information on the size of dechlorinating populations and community structure characteristics obtained above, and the in-place residual congener pattern of PCBs, a method will be developed to determine the current stage of dechlorination or potential for further dechlorination in situ.Progress Summary:
Completed the kinetic studies of dechlorination, including the determination of the rate of dechlorination normalized to the biomass of dechlorinating microorganisms.Completed the investigations on the interactions of methanogens and sulfate reducers on dechlorination in PCB-contaminated sediments.
Determined the population size of dechlorinating microorganisms in PCB-contaminated sediments in the St. Lawrence River in nine different sediments using the most probable number (MPN) technique.
Developed a method to fractionate different dechlorinator populations and estimate their numbers using a combination of serial dilution and MPN techniques.
Investigated 16-S RNA profiles to find group-specific molecular probes for dechlorinating microorganisms by analyzing microorganisms in PCB-free and PCB-spiked sediments for one time point during their growth. We have found difference between the two. At the present, we are investigating whether the difference originates from dechlorinating populations or from other nondechlorinating microorganisms in the sediments.
Investigated any difference in the phospholipid profiles between PCB-free and PCB-spiked sediments for one time point. Data so far have shown only a slight difference. Our investigations are continuing through other time points of growth.
Dechlorination kinetics of PCBs were investigated in Aroclor 1248-spiked sediments at 16 concentrations ranging from 0 to 200 ppm using sediment microorganisms from the Reynolds site in the St. Lawrence River, NY, over a 58-week incubation period. The time course of dechlorination, measured as the total Cl's per biphenyl, consisted of an initial lag phase followed by rapid dechlorination and then a plateau, which represented an apparent end-point of dechlorination. A clear threshold concentration was found between 35 and 45 ppm; there was no dechlorination observed at 7 concentrations below this level. Above the threshold concentration, dechlorination rate was a function of sediment PCB concentration. The rate, calculated as the slope of the rapid phase, was linear within the concentration range investigated. The maximum extent of dechlorination also increased with initial Aroclor concentrations; only 4 percent of Cl per biphenyl was removed at 45 ppm and the removal was saturated at approximately 36 percent above 125 ppm. This difference appeared to be due to whether or not dechlorination involved meta-rich congeners such as 2,2',5-, 2,2',5,5'- and 2,2',3',5-chlorobiphenyl. These results indicate that a major controlling factor for natural remediation potential in sediments is the initial PCB concentration which determines the maximum extent, rather than the dechlorination rate.
The biomass-normalized kinetics of reductive dechlorination of PCBs were also investigated using microbial populations eluted from St. Lawrence River sediments at 10 different concentrations of Aroclor 1248 ranging from 10 to 900 ppm and the time course of dechlorination and population growth were concurrently determined by a congener-specific analysis and the most probable number (MPN), respectively. Dechlorination measured as nmol Cl removed?g sediment-1 was a linear function of Aroclor concentrations, with an intercept at 40 ppm, the threshold concentration below which no dechlorination occurred. Below the threshold level, dechlorinating microorganisms were unable to grow. Above 40 ppm, the specific growth rate of dechlorinating microorganisms was a saturation function of the concentrations which could be fitted by the Monod model. The maximum growth rate was 0.19?day-1 and the half saturation concentration was 0.77 mol Aroclor 1248?g sediment-1. Dechlorination normalized with dechlorinator number over time was first order, because of the exponential nature of the population growth. The first order rate constants were a saturation function of PCB concentrations, with a maximum rate constant of 0.20?day-1 (a half-life of 3.5 days) and a half-saturation constant of 0.70 mol Aroclor 1248?g sediment-1. A positive correlation was found between dechlorination rate (nmol Cl removed?g sediment-1) and the growth rate of dechlorinator populations. These results strongly indicate that PCB dechlorination is tightly linked to growth. They also demonstrate that dechlorinating microorganisms require PCBs for growth.
The potential role of methanogens and sulfate reducers in polychlorinated biphenyl dechlorination was investigated using the specific inhibitors, 2-bromoethanesulfonate (BES) for methanogens and molybdate for sulfate reducers and the most probable number technique. The inhibition of sulfate reducers did not have any effect on Aroclor 1248 dechlorination nor on the size of dechlorinating populations, indicating that they were not directly involved. On the other hand, the inhibition of methanogens reduced the rate and extent of dechlorination, but did not affect the size of dechlorinating populations. These results indicate that there are at least two different dechlorinating populations; one which requires the presence of methanogens for dechlorination and the other which can dechlorinate independently. In the absence of methanogenesis, mostly meta-substituted congeners such as 25-2'5'-, 23-2'5'-, and 25-2'-chlorobiphenyls were not dechlorinated. When both inhibitors were added, there was no dechlorination or growth of dechlorinating microorganisms, probably due to the growth inhibition by the high redox potential which resulted from the suppression of the two major types of anaerobic respiration.
PCB-dechlorinating microbial populations in St. Lawrence River sediments were fractionated and estimated based on the dechlorination pattern using a combination of the serial dilution and most probable number (MPN) techniques. The supernatant of slurries made of PCB-contaminated St. Lawrence River sediments was inoculated to PCB-free sediments spiked with Aroclor 1248. Near the end of the rapid-dechlorination phase, these sediments were serially diluted and each dilution was inoculated into a series of 5 vials containing Aroclor 1248-spiked sediments to estimate the MPN of dechlorinating microorganisms. Two distinctive dechlorination patterns emerged after an 11- month incubation between the inocula of high and low dilutions. In the MPN sediments with a high-dilution inoculum, meta-substituted congeners consisting mainly of 2,5,2',5'-, 2,4,2',5'- and 2,5,2'-chlorobiphenyl were not dechlorinated (Pattern B), with an overall decrease in the average number of Cls' per biphenyl from 4.0 Cls' to 3.4. In MPN sediments with a low-dilution inoculum, these congeners were further dechlorinated (Pattern A) and reduced Cl number decreased from 4.0 to 2.9. These results indicate that there are at least two subpopulations. While Pattern B was produced by Pattern B-producing dechlorinators, Pattern A was produced by a combination of Pattern B producers plus another populations which dechlorinate the meta-rich congeners. When the population size was calculated based on the frequency of respective patterns in the MPN series, the populations yielding Pattern B were approximately 2.4 ? 106 cells?g dry weight sediment-1 whereas the dechlorinators of the meta-rich congeners were two orders of magnitude less at 3.5 ? 104 cells?g dry weight sediment-1. Despite the low number, these meta-dechlorinators in Pattern A increased the overall dechlorination by almost two fold.
Future Activities:
During the next year, we will continue to investigate group-specific molecular probes and biochemical markers (phospholipid fatty acid patterns) for dechlorinating microorganisms in sediments. We also will further investigate the distribution of dechlorinating microorganisms in St. Lawrence River sediments, and determine whether a correlation exists between ambient PCB concentrations and "available Cls" for dechlorinators and the number of dechlorinating microorganisms. Using the newly developed technique to fractionate and enumerate different dechlorinating microbial populations, we will also study change in dechlorinator populations with changes in congener composition as a consequence of dechlorination.Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 24 publications | 8 publications in selected types | All 8 journal articles |
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Type | Citation | ||
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Cho YC, Kim J, Sokol RC, Rhee GY. Biotransformation of polychlorinated biphenyls in St. Lawrence River sediments: Reductive dechlorination and dechlorinating microbial populations. Canadian Journal of Fisheries and Aquatic Sciences 2000;57(Suppl 1):95-100. |
R825449 (1999) R825449 (Final) |
not available |
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Kim J, Rhee GY. Reductive dechlorination of polychlorinated biphenyls: interactions of dechlorinating microorganisms with methanogens and sulfate reducers. Environmental Toxicology and Chemistry 1999;18(2):2696-2702. |
R825449 (1997) R825449 (1999) R825449 (Final) |
Exit Exit |
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Kim J, Rhee G. Population dynamics of polychlorinated biphenyl-dechlorinating microorganisms in contaminated sediments. Applied and Environmental Microbiology 1997;63:1771-1776. |
R825449 (1999) R825449 (Final) |
not available |
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Sokol RC, Bethoney CM, Rhee GY. Effect of Aroclor 1248 concentration on the rate and extent of PCB dechlorination. Environmental Toxicology and Chemistry 1998;17(10):1922-1926. |
R825449 (1997) R825449 (1999) R825449 (Final) |
Exit Exit |
Supplemental Keywords:
biodegredation, polychlorinated biphenyl, reductive dechlorination., Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Remediation, Environmental Chemistry, Contaminated Sediments, Chemistry, Microbiology, Fate & Transport, Biochemistry, fate, sediment treatment, contaminant transport, polychlorinated biphenyls (PCBs), soil sediment, NAPL, contaminated sediment, chemical speciation, sediment transport, adverse human health affects, chemical contaminants, kinetic studies, hazardous waste, contaminated soil, ecological impacts, microbial pollution, geochemistry, assessment methods, ecology assessment models, exposure assessmentProgress 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.