Anaerobic transformation of environmental pollutants by vitamin B(12)
Abstract
Anaerobic microbially mediated reductive dehalogenation has potential as a process for the remediation of sites contaminated with halogenated compounds. While the responsible microbial consortium for reductive dechlorination under natural conditions remains unclear, it is possible that microbial metal-containing coenzymes contribute to reductive dehalogenation reactions in the environment. A biornimetic system mimics biological conditions in terms of temperature, pH, and redox. Reductive dehalogenation examined in a biornimetic system, under mild biologically relevant conditions, is useful for assessing the relative biodegradation potential of PCBs. Two important environmental reactions, reductive dehalogenation and biomethylation are both mediated by the metal-containing coenzyme vitamin B12. The study of the relationship between reductive dehalogenation and biomethylation of metals showed that the in situ induction of anaerobic conditions for enhanced reductive dechlorination does not enhance methylmercury production if the induction substrates are properly chosen. Also, the formation of chloromethylmercury is unlikely under normal environmental conditions. Studies on reductive dechlorination of PCBs using a biornimetic system have shown that ortho dechlorination in the environment is likely limited by the PCB congener substitution pattern which favors meta and para dechlorination over ortho dechlorination. Zero valent zinc can effectively dechlorinate PCBs under ambient conditions. Moreover, PCB dechlorination by zinc is favored at the ortho position, which indicates a possible complementary process for in situ PCB remediation. Debromination of flame retardant PBDEs was observed in anaerobic sediment incubations, in the biomimetic system, and by zero valent zinc. The PBDE debromination rate was much faster in the biomimetic system, which has no bioavailability limitations with a half-life of 10 minutes. In anaerobic sediment, the superhydrophobicity of PBDEs may play a significant role in inhibiting microbial transformation of the compounds.
Degree
Ph.D.
Advisors
Nies, Purdue University.
Subject Area
Environmental science
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