Dechlorination of Persistent Organic Pollutants with Palladized Magnesium: Dioxins and PCNs

The goal of this research is to investigate the reaction of persistent organic pollutants (POPs) other than polychlorinated biphenyls (PCBs) with a NASA provided magnesiumpalladium metal catalyst (Mg/Pd). This work will evaluate the reaction for two important environmental classes of contaminants: polychlorinated naphthalenes (PCNs) and polychlorinated dibenzo-p-dioxins (PCDDs or Dioxins). This evaluation will include work with both pure solvent systems and contaminated sediments. Questions to be addressed include: Is there reactivity with Mg/Pd? What are the end products of the reaction? How fast does it take place? Can dechlorination be demonstrated?

Contaminated sediments are of significant environmental concern. The US EPA estimated in their 1997 report on national sediment quality that approximately 10% of all sediments are sufficiently contaminated to pose an ecological and human health risk. A key issue in this field is the presence of contamination with POPs such as PCBs, Dioxins, polychlorinated dibenzofurans (PCDFs), and PCNs. These POPs are persistent in the environment on a global scale, have been shown to bioaccumulate in animals, and are challenging to treat to safe levels.

A great deal of work has been undertaken by researchers studying and developing treatment approaches for PCBs. To date, a lesser degree of effort has focused on some of the other POPs such as Dioxins or PCNs. In particular, PCNs continue to be a little studied group of environmental toxins. Yet these compounds have been found to be equal if not more significant contributors than PCBs to toxicity levels at certain contaminated sites.

Previous work at UNH has shown that PCBs can be successfully dechlorinated by reaction with palladized magnesium. Preliminary batch experiments working with Dioxins and PCNs in pure solutions suggest comparable results. The method involved spiking a 10% methanol/distilled water solution with a single congener of Dioxin or PCN contaminant. The Mg/Pd powder was added to the reaction vial and the solution was mixed for 30 minutes. The mixture was hand extracted with hexane or toluene at the end of the reaction time and a sample was taken for GC/MS analysis. The quantity of the contaminant was significantly reduced for all compounds tested as may be noted in Figures 1 through 3. No degradation byproducts were observed in these experiments as was noted in previous experiments conducted by UNH researchers working with PCBs and Mg/Pd.

 

 

 

 

A second set of batch experiments were run with 1,2,3,4-Tetrachloronaphthalene (TCN) and Octachlorodibenzo-p-dioxin (OCDD) to evaluate the reaction kinetics and to identify byproducts that may form quickly and then break down. Samples were reacted for 1, 3, 10, and 30 minutes. This set of experiments showed that 89% of the initial TCN and 66% of the OCDD had disappeared after only 1 minute of the reaction (see Figure 4). Again, no degradation byproducts were observed with the GC/MS.

 

Ongoing work will include:
- Continued efforts to confirm dechlorination and locate the reaction end products
- Experiments with contaminated sediments, to include samples from the highly contaminated Passaic River

 

Contact Information

Dr. Kevin Gardner
Director
Center for Contaminated Sediments Research
336 Environmental Technology Building
University of New Hampshire
Durham, NH 03824
603-862-4334 [phone]
603-862-3957 [fax]
kevin.gardner@unh.edu