Grantee Research Project Results
Final 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: 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 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 research project were 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) in the course of dechlorination; (2) the kinetics of dechlorination based on population-normalized rates. Since polychlorinated biphenyl (PCB) dechlorination is very slow and the population size of dechlorinating organisms and community composition may also 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, we will develop a method to determine the current stage of dechlorination or potential for further dechlorination in situ.
Summary/Accomplishments (Outputs/Outcomes):
To understand the dynamics and structure of the PCB dechlorinating microbial community, dechlorinating microbial populations in St. Lawrence River sediments were investigated using the dilution fractionation and the most probable number (MPN) techniques. We found at least two subpopulations, judging from the final dechlorination patterns. When the populations responsible for each pattern were further investigated, the number of one group was about two orders of magnitude less than that of the other. Despite this low number, they increased the overall dechlorination by almost twofold. The smaller group appears to be responsible for the further dechlorination of the meta-substituted congeners such as 25-2'5'-, 23-2'5'-, and 25-2'-chlorobiphenyls.
Investigations on the interactions of PCB-dechlorinating microorganisms with methanogens and sulfate reducers revealed that the inhibition of sulfate reducers by molybdate had no effect on aroclor 1248 dechlorination or on the size of dechlorinating populations. On the other hand, the inhibition of methanogenesis by 2-bromoethanesulfonate reduced the rate and extent of dechlorination. However, this inhibition did not affect the size of dechlorinating populations. These results show that there are at least two different dechlorinating microbial populations, one of which requires the presence of methanogens for dechlorination and the other of which can dechlorinate independently. In the absence of methanogenesis, meta-substituted congeners, such as 25-2'5'-, 23-2'5'-, and 25-2'-chlorobiphenyls, were not dechlorinated.
The dechlorination kinetics of aroclor 1248 were investigated using microbial populations eluted from St. Lawrence River sediments, which were contaminated mostly by the same aroclor. The time course of dechlorination and population growth were concurrently determined by a congener-specific analysis and the MPN, respectively. Dechlorination rate (nmol Cl removed g sediment-1 day-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 fit by the Monod model. The maximum growth rate was 0.2 day-1 and the half saturation concentration was 0.77 µmol aroclor 1248 g sediment-1.
Dechlorination normalized with dechlorinator number over time. 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 day-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.
Kinetics of PCB dechlorination were similarly investigated for Hudson River sediment microorganisms using aroclor 1242. Dechlorination rate (nmol Cl removed g sediment-1 day-1) was a linear function of PCB concentrations similar to the dechlorination of aroclor 1248 by sediment microorganisms from the St. Lawrence River. However, the rate was much slower, with the linear slope only 24 percent of St. Lawrence's value. The intercept of the linear slope, which indicates a threshold concentration below which no dechlorination occurs, was about three times higher than that for the dechlorination of aroclor 1248. The maximum extent of dechlorination was greater at higher aroclor concentrations. The lag phase before dechlorination appeared to be longer at lower aroclor 1242 concentrations. Dechlorinating microorganisms did not show any significant growth until late in the lag phase of dechlorination, and their maximum was greater at higher initial aroclor 1242 concentrations. Although dechlorination rates were significantly lower with the Hudson River inoculum, when normalized to the maximum number of dechlorinating organisms, they were not significantly different from those for aroclor 1248 by St. Lawrence River microorganisms. These results further support the hypothesis that PCB dechlorination is tightly coupled to the growth of dechlorinating microorganisms.
Investigations on PCB dechlorination in dredged sediments have also revealed that PCB-dechlorination is directly coupled to the growth of dechlorinating microorganisms. The level of dechlorination decreased with moisture contents, and the population size of dechlorinating microorganisms was also smaller at the lower moisture levels. When the maximum extent of dechlorination was plotted against the specific death rate of dechlorinating populations, a significant correlation was found. These results indicate that the underlying mechanism of the moisture-dependent maximum dechlorination is the moisture-dependence of the death rate of dechlorinating microorganisms.
We investigated in situ dechlorination of PCBs in historically contaminated sediments in the St. Lawrence River in relation to the population size of dechlorinating microorganisms. An analysis of six sediment cores and five sections of one core showed that the total PCB concentration and the number of dechlorinators ranged from 14 to 1336 ppm and with 9.7 x 103 to 1.5 x 107 MPN units g sediment-1 (dry weight), respectively. There was no correlation between total PCB concentrations and dechlorinator numbers. However, the population size was significantly correlated (P < 0.007) to the extent of dechlorination (expressed as the average number of Cl per biphenyl or the ratio of meta + para Cl to ortho Cl) of sediment PCBs. Although more data points are needed, the results thus far suggest that the number of dechlorinating microorganisms might be used to predict dechlorination potential in PCB-contaminated St. Lawrence River sediments.
To develop techniques that artificially enrich PCB-dechlorinating microorganisms, non-PCB haloaromatic compounds (chlorobenzoates, chlorophenols, and chlorobenzenes) were investigated for the enrichment of PCB dechlorinating microorganisms and enhancement of PCB dechlorination, using sediment microorganisms eluted from St. Lawrence River sediments. When the inoculum was enriched with each of the 15 haloaromatic compounds (HACs) in PCB-free sediments through 3 sequential transfers after a 5-week incubation, PCB-dechlorinating microorganisms were found in all but pentachlorophenol-enriched sediments. When sediments spiked with aroclor 1248 were amended with HACs, PCB dechlorination was found with all HACs, except pentachlorophenol. In HAC-amended sediments, PCB dechlorination started after a long lag when the HACs were reduced to a very low level; there was no such lag in HAC-free sediments. Despite the lag in the HAC-amended sediments, the rate of PCB dechlorination was faster once it started. The maximum level of dechlorination was also higher, except in sediments with pentachlorobenzene. Of the 13 effective HACs, 6 enhanced only meta-dechlorination; the remaining 5 significantly enhanced both meta- and para-dechlorination (p < 0.05). No HAC was effective for paradechlorination alone. The MPN number of dechlorinating microorganisms was higher with HAC amendment except pentachlorophenol. When the maximum extent of dechlorination at the plateau phase was plotted against the highest number of PCB dechlorinating microorganisms for each HAC, there was linear relationship (p < 0.01). It appears, therefore, that PCB dechlorination was directly linked to the growth of dechlorinating microorganisms and the enhancement of PCB dechlorination by HACs was through the increase in their population size.
Journal Articles on this Report : 8 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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Cho YC, Kwon OS, Sokol RC, Bethoney CM, Rhee GY. Microbial PCB dechlorination in dredged sediments and the effect of moisture. Chemosphere 2001;43(8):1119-1126. |
R825449 (Final) |
not available |
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Cho YC, Sokol RC, Rhee GY. Kinetics of polychlorinated biphenyl dechlorination by Hudson River, New York, USA, sediment microorganisms. Environmental Toxicology and Chemistry 2002;21(4):715-719. |
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 GY. Reductive dechlorination of polychlorinated biphenyls as affected by sediment characteristics. Chemosphere 2001;44(6):1413-1420. |
R825449 (Final) |
not available |
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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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Rhee GY, Sokol RC, Bethoney CM, Cho YC, Frohnhoefer RC, Erkkila T. Kinetics of polychlorinated biphenyl dechlorination and growth of dechlorinating microorganisms. Environmental Toxicology and Chemistry 2001;20(4):721-726. |
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:
polychlorinated biphenyl, PCB, aroclor, dechlorination, dechlorination kinetics, dechlorinating microorganisms, growth kinetics, bioremediation, moisture, death rate., 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.