Grantee Research Project Results
2000 Progress Report: Modeling Microbial PCB Degradation and Binding
EPA Grant Number: R826652Title: Modeling Microbial PCB Degradation and Binding
Investigators: Balaz, Stefan
Institution: North Dakota State University Main Campus
EPA Project Officer: Aja, Hayley
Project Period: September 1, 1998 through August 31, 2001 (Extended to August 31, 2002)
Project Period Covered by this Report: September 1, 2000 through August 31, 2001
Project Amount: $375,000
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Air , Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities
Objective:
The objective of this research project is to develop a complete kinetic description of the fate of individual PCB congeners in aqueous media as determined by structure and physicochemical properties of congeners.
Progress Summary:
The 1-octanol/water partition coefficients Kow were measured for individual PCB congeners in two technical mixtures of PCB: Delor 103 (corresponding to Aroclor 1242) and Delor 106 (corresponding to Aroclor 1260). For congeners that were present in both mixtures, small but systemic deviations were observed between the Kow values measured in the two mixtures. The measured log Kow values are lower than published data measured for single congeners and predicted by the ClogP method that is based on experimental log Kow values of single congeners.
In the suspension of Pseudomonas stutzeri, the time courses of two PCB amounts, evaporated (ms) and remaining in the aqueous phase with the biomass (ml = ma + mm, the subscripts a and m refer to the aqueous phase and biomass, respectively), were determined by congener-specific gas chromatography. The kinetics for individual congeners were described by a compartmental model comprising the exposure time, the degradation rate constant kd, the apparent evaporation rate constant kev, the sorption coefficient for biomass Kp = ki/ko, and the biomass concentration X Figure 1. A kinetic scheme of the PCB fate in the suspension of bacterial biomass. In the aqueous phase, PCB can bind to the extracellular colloidal particles with the association constant Kb.(Figure 1). The parameters were optimized by non-linear regression analysis using both amounts, ms and ml simultaneously, to utilize all available information. Some of the parameters were determined in independent experiments (kev in the aqueous medium, an estimate of Kp in non-degrading microbial suspension) and their values agree closely with the current estimates measured in the presence of degrading microbial biomass. The degradation rate constants kd that characterize the primary step in metabolism are structure-specific and vary within three orders of magnitude. No correlation with structure was obtained. We believe that the obscure structure/degradation relationship is due to binding of the congeners to the active site of the degrading enzyme in several orientations. To account for this phenomenon, we modified current methods of receptor mapping and 3D-quantitative structure-activity relationships (3D-QSAR). The data were submitted to the Free-Wilson analysis and the Comparative Molecular Field Analysis. The results are encouraging, but as of this writing, there are no final conclusions available.
Figure 1. A kinetic scheme of the PCB fate in the suspension of bacterial biomass. In the aqueous phase, PCB can bind to the extracellular colloidal particles with the association constant Kb.
Future Activities:
The degradation rate constants will be subjected to the receptor mapping procedure considering multiple binding modes. The measurement of the partition coefficients of about thirty PCB congeners, both individually and in mixtures will be attempted using the so-called slow-stirring method (de Bruijn, et al). Interactions of PCB congeners with individual soil components and complete soils after a yearlong incubation will be studied by extraction and NMR methods. Degradation of PCB in soils will be monitored and described in similar way as for the liquid media.
Journal Articles:
No journal articles submitted with this report: View all 39 publications for this projectSupplemental Keywords:
quantitative structure-activity relationships, QSAR, quantitative structure-time-activity relationships, QSTAR, biosorption, hydrophobicity, lipophilicity., RFA, Air, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Waste, Toxics, National Recommended Water Quality, Remediation, Ecological Indicators, Ecological Risk Assessment, Ecosystem Protection, Environmental Chemistry, Ecosystem/Assessment/Indicators, Engineering, Chemistry, & Physics, Ecological Effects - Environmental Exposure & Risk, Bioavailability, Bioremediation, Physics, quantitative structure activity relationship, ecological effects, fate of PCB congeners, binding, microbial degradation, dioxin, bioremediation model, bioremediation of soils, human exposure, hydrophobic chemicals, soil, aquatic ecosystem, risk assessment, aquatic, biostabilization of PCBs, PCB, polychlorinated biphenyls, fate and transport, furans, decontamination of soil and water, enzymes, ecological exposure, chemical kinetics, bioacummulation, chemical transport, PCBs, physicochemical, biokinetic model, modelingRelevant Websites:
http://www.ndsu.nodak.edu/instruct/balaz/pcbdegr.htm 
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.