Grantee Research Project Results
1997 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, 1997 through December 31, 1998
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. Since PCB dechlorination is very slow taking place over months 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.Progress Summary:
(1) Established a protocol to enumerate PCB-dechlorinating bacteria using the Most-Probable-Number(MPN) technique.
(2) Population dynamics of dechlorinating microorganisms and their interactions with methanogens and sulfate reducers were determined.
(3) A determination of the dechlorination kinetics of Aroclor 1248 by sediment microorganisms in the St.Lawrence River is in progress.
(4) Studies are under way to identify specific patterns of phospholipid fatty acids (PLFAs) as potential biomarkers for dechlorinating microorganisms.
(5) Experiments are in progress to determine dechlorinator populations in PCB-contaminated natural sediments in the St. Lawrence River.
Accomplishments and Research Results:
We have established and validated the protocol of the most-probable-number (MPN) technique forthe enumeration of PCB-dechlorinating microorganisms. First, a dilution series (10-1 - 10-9) of each sample is prepared by serially transferring 1 ml after vigorous vortex mixing. Each dilution is then inoculated into5 MPN replicate vials which contain 2,3,4- and 2,5,3',4'-chlorobiphenyls at 150 ppm each (on a sedimentdry weight basis). The number of dechlorinators was estimated by assaying the dechlorination of the two congeners in the MPN vials. Vials were considered dechlorination positive if dechlorination occurred after 16 weeks of incubation.
Using the MPN protocol, we have investigated for the first time the population dynamics of these organisms and their interactions with two major anaerobic respirators in sediments, methanogens and sulfate reducers, using the MPN technique and specific metabolic inhibitors of each group (e.g. molybdate & 2-bromoethanesulfonate). Dechlorinators were found to require PCBs for growth. A fractionation of dechlorinating populations by the dilution technique showed that there are at least two subpopulations of different sizes judging from their dechlorination competence. Of these two, only the smaller subpopulation appeared to be able to dechlorinate meta-rich congeners such as 2,5,2',5'-, 2,3,2',5', and 2,5,2' whereas the larger one appeared to be unable to further dechlorinate them. The smaller subpopulation also required the presence of methanogens for dechlorination. Sulfate reducers appeared to play no role.
The support of EPA also enabled us to expand the on-going investigation of dechlorination kineticsof PCBs using Aroclor 1248 and sediment microorganisms from the Reynolds site in the St. Lawrence Riverwith a more frequent regime of measurements for an accurate rate determination and a longer experimental period extending to 58 weeks. 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 was linear within the concentration range investigated. The maximum extent of dechlorination also increased with initial Aroclor concentrations. This difference appeared to be due to whether or not dechlorination involved meta-richcongeners such as 2,2',5-, 2,2',5,5'- and 2,2',3',5-chlorobiphenyl. These results indicate that a majorcontrolling factor for natural remediation potential in sediments may be the initial PCB concentration which determines the maximum extent, rather than the dechlorination rate.
The kinetic studies, however, did not reveal whether the concentration-dependence of dechlorination was an expression of enzyme affinity or difference in the size of dechlorinator populations, since the rate used was not normalized with biomass. In light of our finding that dechlorinators require PCBs for growth, it is quite possible that the size of biomass is proportional to PCB concentrations in a certain range. The concentration range employed in this study (0 to 200 ppm) was also too low to reveal the saturation range. Therefore, new experiments are under way with an upper concentration range of 900 ppm and with the concomitant measurement of dechlorination and the biomass of dechlorinators.
To develop a method to use phospholipid fatty acids (PLFA) as a biomarker and measure of the biomass of dechlorinators, an anaerobic microcosm was set up with PCB-spiked sediments. The time courseof dechlorination was then followed with a concomitant measurement of biomass with both MPN technique and PLFA extraction. In PCB-spiked sediments, the growth of dechlorinators as determined by the MPNtechnique mirrored the time course of dechlorination. In PCB-free sediments, however, no growth was detected. On the other hand, the measurement of PLFA did not show any significant difference between PCB-spiked and -free sediments. These PLFA results may in part be due to the relatively small sample size employed for their extraction and analysis. This work will soon be repeated.
Future Activities:
During the next year, we will continue our dechlorination kinetic studies utilizing an even broader range of PCB concentrations (up to 900ppm) along with the estimation of the biomass of dechlorinators a teach concentration, using the MPN technique. We will also expand our investigation on the microbial population dynamics to further characterize the different subpopulations involved in the PCB dechlorination process. New experiments will be setup to determine the difference in PLFA patterns between PCB-spiked and -free sediments and to monitor any changes in the PLFA pattern during the time course ofdechlorination. A revised protocol using a larger sample size for extraction will be employed. Work will also begin on assessing changes in community structure using group-specific molecular probes during the timecourse of dechlorination.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 24 publications | 8 publications in selected types | All 8 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
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 |
|
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:
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.