Abstract:
Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated
dibenzofurans (PCDFs) are compounds of considerable environmental concern due to their persistence
and toxicity. These halogenated compounds have become ubiquitous pollutants because they can be
accidentally released after they are formed as unwanted by-products during synthesis of halogenated
aromatic compounds or during incineration of industrial or domestic wastes and they are disseminated
to the less populated parts of the earth [1]. In addition to being recalcitrant in the environment,
many of PCDDs/Fs congeners are extremely toxic and carcinogenic to human [2,3]. The structures of
PCDD/Fs are chemically very stable due to the absence of reactive groups, and hence these compounds
are decomposed very slowly in the environment [4]. Over the last decade, several treatment methods
were developed using physical, chemical, and even biological based approaches.
Large number of bacterial strains that are of degrading DD, DF and their analogues via lateral
and angular dioxygenation have been isolated and characterized. Dioxin degradation through angular
dioxygenation has been extensively investigated since it led to complete mineralization of DD, DF
and few of their mono chlorinated congeners [5-7]. Consequently, numerous studies have been carried
out to elucidate the aerobic bacterial degradation of PCDD/Fs compounds. However, the degradation
capability extended to only low chlorinated congeners and degradation ability is hampered by
chlorination pattern. The reductive dechlorination of PCDD/Fs by anaerobic microorganisms is
a promising method to bioremediation. More intensive studies on dechlorination of PCDD/Fs have
been carried out over a decade. Microbial dechlorination of PCDD/Fs occurs in sediments and
anaerobic mixed cultures from sediments. Dechlorination of environmentally significant dioxins
by pure culture of Dehalococcoides sp. CBDB1 has been reported recently [8]. Under anaerobic
conditions PCDD/Fs are converted into less chlorinated derivatives. However, the microbial
dechlorination of PCDD/Fs often produces much more toxic congeners, including 2,3,7,8-TCDD [9].
The anaerobic transformation rates for PCDD/Fs are too slow to be taken into account for
bioremediation of these ubiquitous pollutants. Alternatively, construction of gene cassette
carrying all genes for PCDD/Fs degradation could be of potential for detoxification of these
compounds.
Reductive dehalogenation using zero-valent iron (ZVI) has been studied extensively for the
remediation of halogenated aliphatic contaminants, including carbon tetrachloride,
1,1,1-trichoroethane, and trichloroethylene [10-12]. In contrast, few studies have examined
the dehalogenation of halogenated aromatics by ZVI, and they involved only a limited range of
chlorinated phenols [13-15], polybrominated diphenyl ethers [16], and polychlorinated biphenyls
[17]. The only published report on the dechlorination of polychlorinated dibenzo-p-dioxins (PCDDs)
using ZVI is a preliminary study that we performed with PCDD/Fs-contaminated fly ash [18]. The
toxicity of PCDD/F congeners varies greatly, with 2,3,7,8-TeCDD being the most toxic, so incomplete
dechlorination starting with the more highly chlorinated PCDD/Fs can increase the net toxicity of
mixtures. To avoid this, effective remediation of PCDD/Fs requires not only fast dechlorination of
the parent compounds, but also rapid conversion of the parent compounds to non-toxic products.
Recent achievements in degradation, adsorption and remediation of highly chlorinated PCDD/Fs by
biological and chemical treatments are discussed here.
Brief Biography of the Speaker:
I finished my BS degree in Chemistry at
Yonsei University in Seoul, Korea. And then I moved to U.S. and I did
my Ph.D. work at Oregon State University in the Department of
Chemistry, under the supervision of Professor Max L. Deinzer (Emeritus
at present). The subject of my Ph.D. was in the field of physical and
analytical chemistry of environmental pollutants based on the several
advanced mass spectrometers especially for the polychlorinated
dibenzo-p-dioxins and polychlorinated diphenyl ethers. After the
completion of Ph.D. work, I moved to Michigan State University and
worked as a post doctoral researcher in the Department of Biochemistry
(with Prof. Jack Throck Watson). At there, I grafted my analytical
backgrounds to the identification of biological molecules such as
proteins and carbohydrates. In the next place for my second Post Doc,
I worked with Prof. Klaus Biemann (also Emeritus at present) in the
Department of Chemistry at MIT, Massachusetts for profound research on
the mass spectrometric analysis of core biomolecules.
After my Post doc experiences in U.S., I joined the Korea Basic
Science Institute for mass spectrometry research and I converged all
my efforts to the installation of high resolution tandem mass
spectrometers. Following my period in the institute, I move to Hanyang
University in Seoul as an assistant professor in the Department of
Chemistry. However, not long after, I joined the School of
Environmental Science and Engineering at POSTECH (Pohang University of
Science and Technology) which was recently founded for advanced
science and engineering research with full supports by POSCO Co. (one
of the largest steel company over the world).
I firstly did my efforts to the installation of the central analytical
center at the university and now that the facility is equipped with
many high throughput mass spectrometers and other instruments for
environmental pollutant analysis. After establishment of well
constituted analytical infra, I enlarged my research area from the
pollutant analysis to the environmental monitoring and advanced
treatment of toxic pollutants. In these days, I am focusing my
research on the degradation of harmful chemicals by bacteria and fungi
through identification of their intermediates in the bio-reactions. At
the same time, we are employing nano scale zero valent iron (nZVI) to
the dehalogenatic detoxification of highly halogenated environmental
pollutants including chlorinated dioxins and brominated diphenyl
ethers. Now we have published more than 100 papers in various
international peer reviewed journals, such as Analytical Chemistry,
Environmental Science & Technology, Applied and Environmental
Microbiology, and etc. We are contiuing our efforts to develop a best
available technology to remediate very toxic chemicals from the
environment by combination of chemical and biological means and this
can be also accomplished with collaborations with many domestic and
foreign researchers. |
