Grantee Research Project Results

1998 Progress Report: Modeling Microbial PCB Degradation and Binding

EPA Grant Number: R826652
Title: 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, 1998 through August 31, 1999
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 kinetics of distribution of PCBs in soil and aqueous media is governed by evaporation, adsorption to solid particles and biomass, and by microbial degradation. The proposed research aims at (1) development of a complete kinetic description of the fate of individual PCB congeners in aqueous media and soils as determined by structure and physicochemical properties of congeners, biomass, and soils and (2) QSAR formulation considering multiple binding modes for binding of PCBs to the degrading enzyme and for published data on binding of polychlorinated aromatic pollutants with symmetrical skeletons to toxicologically relevant proteins.

Progress Summary:

The kinetics of distribution between biomass of Pseudomonas stutzeri, an aqueous medium and the gas phase was monitored for about fifty PCB congeners in a technical mixture. To reduce the number of processes affecting the fate of the congeners, the biomass was inactivated using 3-chlorobenzoic acid that inhibits PCB degradation. The kinetics were described by a compartmental model comprising the exposure time, the evaporation rate constant k_ev, the association constant K_X, and the biomass concentration. The association constant K_X may include, in addition to the sorption coefficient for biomass, the association constant for binding to extracellular colloidal material. Accumulation in biomass and binding to the colloidal particles could not be distinguished in this experimental setting. The main property of the PCB congeners determining both the rate of evaporation and sorption is lipophilicity of the compounds expressed as the decadic logarithm of the 1-octanol/water partition coefficient P. Due to lack of reliable P values for many of the tested congeners, the values calculated by the ClogP software were used. The evaporation rate constant k_ev is negatively correlated to lipophilicity. The association constant K_X is proportional to lipophilicity. In both cases, the trends are obvious, although closer correlations would be advantageous for more reliable predictions. Further possibilities of correlating k_ev and K_X with structural and electronic properties of the chemicals are being examined.

Binding of PCB congeners to degrading enzymes will be analyzed using our receptor mapping techniques that consider possibility of multiple binding modes. The experience with similar symmetric molecules indicates that multiple binding modes are an important factor contributing significantly to quality of the models. This conclusion was confirmed by analysis of published data (Safe et al.) on binding of polychlorinated dibenzofurans to aryl hydrocarbon receptor. Using all published data, a good quality receptor map was derived that also explained correctly the binding affinities of the congeners that were not included in the analysis because only semi-quantitative binding data were available for them.

Future Activities:

A kinetic analysis of distribution and degradation of about fifty PCB congeners will be performed in the suspension of Pseudomonas stutzeri cultivated in a liquid medium. The experimental setting will be similar as in monitoring of the PCB distribution alone, so that the parameters characterizing evaporation and sorption of PCB congeners could be transferred between the two systems. This design should provide for determination of reliable degradation rate constants of individual congeners.

The degradation rate constants will be subjected to the receptor mapping procedure considering multiple binding modes.

The quality of correlations between evaporation rate constant k_ev, the association constant K_X, and lipophilicity could possibly be improved by the use of reliable experimental values of the partition coefficients for all tested congeners. 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).

Journal Articles:

No journal articles submitted with this report: View all 39 publications for this project

Supplemental Keywords:

quantitative structure-activity relationships (QSAR), quantitative structure-time-activity relationships (QSTAR), biosorption, hydrophobicity, 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, modeling

Relevant Websites:

http://www.ndsu.nodak.edu/instruct/balaz/pcbdegrb.htm Exit EPA icon

Progress and Final Reports:

Original Abstract

The 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.