Investigating Microbial Degradation of Polychlorinated Biphenyls Using Molecular IsotopesEPA Grant Number: R828161
Title: Investigating Microbial Degradation of Polychlorinated Biphenyls Using Molecular Isotopes
Investigators: Reddy, Christopher M. , Eglinton, Timothy I. , Wirsen, Carl O.
Institution: Woods Hole Oceanographic Institution
EPA Project Officer: Lasat, Mitch
Project Period: July 7, 2000 through September 30, 2003
Project Amount: $196,743
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry
The stable isotope effects associated with microbial degradation of polychlorinated biphenyls (PCBs) by reductive dehalogenation will be investigated. Specifically, we will determine the extent to which bacteria fractionate the stable isotopes of chlorine, hydrogen, and carbon of PCBs in laboratory enrichment cultures and then isotopically compare PCB degradation reactants and products from the laboratory enrichment cultures to extracted PCB samples from Areal-world@ marine sediments.
We will isotopically analyze individual PCB congeners using newly developed methods for chlorine and hydrogen stable-isotope ratio measurement and standard methods for carbon stable-isotope ratio measurement. Small but measurable differences in the isotope ratio of these compounds exist because kinetic and thermodynamic properties are dissimilar for any one isotopically different congener (termed an isotope effect). We propose to investigate the isotope effects associated with reductive dehalogenation, which is the major environmental removal process of tetra- to deca-chlorinated PCB congeners.
Microbes isolated from contaminated sediments will be used to inoculate laboratory cultures. The cultures will be spiked with individual PCB congeners and incubated under anaerobic conditions. The reactant and product concentrations and the isotopic compositions of carbon, chlorine, and hydrogen in each individual congener will be monitored. We will also determine the isotopic abundances of PCB congeners that are extracted from New Bedford Harbor sediment and compare our results to the laboratory enrichment cultures. Results from these two independent studies will be contrasted to assess any differences in laboratory cultures and actual environmental conditions, elucidate the mechanisms of reductive dehalogenation, and understand the isotopic signals that are carried in PCB congeners and their degradation products.
This novel, interdisciplinary study will: (i) allow for the first systematic investigation of Cl and H isotopic characteristics of semi-volatile chlorinated organic contaminants; (ii) allow for a refined assessment of how bacteria microbially degrade PCBs; and (iii) provide a direct means of correlating laboratory and field studies of microbial degradation of PCBs at natural isotopic abundance. This study will also provide a new perspective on PCBs and be very useful in managing and assessing the risks and fates of PCBs in the environment.