The Mitch Laboratory
RESEARCH BACK
While PCBs have been banned in the US, we continue to produce a host of structurally similar chemicals.
Persistent Organic Pollutant Destruction by Sulfides and Black Carbons
Hydrophobic persistent organic pollutants (POPs), particularly those with nitro or halogen substituents, remain a critical and on-going, global concern. Although the production of polychlorinated biphenyls (PCBs) and chlorinated hydrocarbon pesticides (e.g., lindane) is being phased out worldwide, production of high volumes of a host of structurally similar compounds continues. As a result of their hydrophobic characteristics, these compounds tend to associate with sediments or bioaccumulate to high concentrations in the fatty tissues of organisms at the top of the food chain, including humans. Certain POPs are associated with toxicity, including carcinogenicity (e.g., PCBs) and liver toxicity (e.g., PBDEs).
Recent research indicates the dominant role that black carbons occurring in sediments, such as soots and chars, play in sorbing POPs. Indeed, activated carbon, a synthetic black carbon, has been applied to sediments to sequester POPs, dramatically reducing their bioavailability to benthic species. While their sorptive role is well-recognized, black carbons also exhibit reactive functional groups, such as quinones. We seek to understand how black carbons mediate pollutant destruction in the presence of sulfides for POP destruction, so we can design less persistent and problematic chemicals in the future.Case Study: Bombing Ranges
Like TNT, the explosive compound RDX is a common contaminant of military bombing ranges, such as the Vieques bombing range in Puerto Rico. We found that RDX was rapidly destroyed by sulfides in the presence of black carbon, forming nitrite and formaldehyde, rather than the toxic nitrosated reduction products formed by other remediation techniques. Black carbons and sulfides tend to co-occur in marine sediments without human intervention. This technology may be particularly pertinent for unexploded ordinance (UXO) sites in marine areas (e.g., Vieques, Puerto Rico), where alternative in-situ technologies requiring excavations (e.g., zero-valent iron cutoff trenches) may be dangerous. The co-occurrence of sulfides and black carbons in these areas may provide a protective blanket underneath bombing ranges, where the locations of UXO are often poorly characterized.
| Like
TNT, the explosive compound RDX is a common contaminant of military bombing
ranges, such as the Vieques bombing range in Puerto Rico. We found that RDX was rapidly destroyed by
sulfides in the presence of black carbon, forming nitrite and formaldehyde,
rather than the toxic nitrosated reduction products formed by other remediation
techniques. Black carbons and sulfides tend to co-occur in marine
sediments without human intervention. This technology may be particularly pertinent for unexploded ordinance
(UXO)
sites in marine areas (e.g., Vieques, Puerto Rico), where alternative in-situ
technologies requiring excavations (e.g., zero-valent iron cutoff trenches) may
be dangerous. The co-occurrence of
sulfides and black carbons in these areas may provide a protective blanket
underneath bombing ranges, where the locations of UXO are often poorly
characterized. For more information, see:
Kemper, J.; Ammar, E.; Mitch, W.A. Abiotic degradation of RDX in the presence of hydrogen sulfide and black carbon. Environ. Sci. Technol., Research ASAP. |
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