Enhanced Microbial Dechlorination of PCBS and Dioxins in Contaminated Dredge Spoils:
Max M. Häggblom and Cecilia Vargas, Rutgers University


Goal:


The goal of the current project is to develop and demonstrate the feasibility of a microbial technology for remediation of sediments contaminated with mixtures of PCBS, dioxins and chlorinated pesticides. The focus is on identifying environmental conditions and amendments that can initiate dechlorination by indigenous microbial communities. Biological processes based on the metabolic activities of anaerobic bacteria are attractive since reductive dechlorination of PCBS, dioxins and chlorinated pesticides can significantly reduce the toxicity of the sediments, and have the potential for complete degradation of the contaminants. Reducing the toxicity of the sediments and dredge spoils would allow for alternative disposal solutions or beneficial uses.

Rationale:


The goal of the current project is to develop and demonstrate the feasibility of a microbial technology for remediation of sediments contaminated with mixtures of PCBS, dioxins and chlorinated pesticides. The focus is on identifying environmental conditions and amendments that can initiate dechlorination by indigenous microbial communities. Biological processes based on the metabolic activities of anaerobic bacteria are attractive since reductive dechlorination of PCBS, dioxins and chlorinated pesticides can significantly reduce the toxicity of the sediments, and have the potential for complete degradation of the contaminants. Reducing the toxicity of the sediments and dredge spoils would allow for alternative disposal solutions or beneficial uses.

Approach:


Anaerobic dehalogenation of chlorinated compounds in contaminated sediments has been widely demonstrated, and this makes in-situ biological remediation of contaminated sediments a potential treatment solution. The naturally occurring dechlorination unfortunately has a number of short-comings:

  1. The transformation rate is extremely slow, especially at lower PCB levels such as those found in the New York/New Jersey Harbor, and

  2. The presence of sulfate in marine sediments may inhibit dechlorination. Furthermore, since the sediments are contaminated with a mixture of chlorinated contaminants (PCBS, dioxins, DDT residues) methodologies that would stimulate the dechlorination (and detoxification) of all these components are needed. The intrinsic rates of PCB, dioxin and DDT dehalogenation need to be significantly enhanced for a bioremediation technology to be practical.

The approach of the proposed project is to identify conditions and chemical amendments for stimulating dechlorination by microbial populations present in the contaminated sediments, focusing on how to stimulate intrinsic microbial populations to dechlorinate and degrade PCBS and dioxins at the existing levels by:

  1. Stimulation of a dehalogenating microbial population by the addition of a brominated aromatic compound or a single PCB congener;
  2. Addition of alternative carbon sources (fatty acids, methanol, etc.) to provide a carbon and energy source to drive reductive dechlorination;
  3. Examination of the influence of sulfate on dechlorination. Sulfate levels can be reduced by the addition of appropriate carbon sources stimulating sulfate reduction, and carbon additions can therefore serve a two-fold purpose.

Status:


Our ongoing work has advanced the understanding of the role of diverse anaerobic microbial communities in the degradation of halogenated aromatic compounds, and how their activities can be exploited for remediation of contaminated sediments. We have demonstrated that the dechlorination of PCBS and dioxins in the estuarine sediments of the NY/NJ Harbor can be stimulated by addition of additives. High sulfate concentrations inhibit dechlorination and dechlorination was only observed under methanogenic conditions. 2,3,4,5,6-Pentachlorobiphenyl was sequentially dechlorinated at the para and meta positions to 2,6-dichlorobiphenyl and 2,4,6-trichloro-biphenyl and primed the dechlorination of Aroclor 1260. We have also demonstrated that dioxins can be reductively dechlorinated by microorganisms in the harbor sediments, using 1,2,3,4-tetrachloro-dibenzo-dioxin as a model. In methanogenic sediment slurries 1,2,3,4-tetraCDD was dechlorinated in the lateral position to 1,2,4-triCDD, and further to a diCDD. Whether this lateral dechlorination can be stimulated for polyCDDs is central to their detoxification. The project will continue the initial exploratory work necessary for the future consideration of bioremediation as a possible method of decontaminating dredge spoils sediment, either as an in-situ / intrinsic process or in a bioreactor-type setting of dredged sediments.


Technology
Transfer
and
Outreach
Plan:


At the Biotechnology Center, the transfer of new discoveries to industry is aided by cooperative research programs with New Jersey's agricultural, chemical, pharmaceutical, bioremediation, and biotechnology corporations. The center pursues a variety of strategies to accelerate the application of its research results and serve industry's needs. These range from individual research contracts, site visits, and advisory assistance for entrepreneurial new companies, to innovative partnerships with industry funded by the New Jersey Commission on Science and Technology. Two entrepreneurial companies specializing in environmental clean-up have been launched with the Center's support: Envirogen (Princeton) and Phytotech (Monmouth Junction). These Biotech Center - industry connections provide strong partnerships for the technology transfer process.