Chemistry International
Vol. 21, No. 6
November 1999
News
from IUPAC
Biodegradation
of Chemical Warfare Agents
Newer CW Biodegradation Research
Efforts Show Progress
Several Approaches to Biodegrading Nerve
Agents
Other Microorganisms with CW Hydrolytic Enzymes
Identified
Strategies for Degrading Bulk Agents
Biodegrading the Blistering Agents
HD and HT
Strategies for Degrading Organo-arsenical
Blistering Agents
Unanswered CW Degradation Questions Require Further
Research
Acknowledgments
Suggested Reading
Strategies for Degrading
Organo-arsenical Blistering Agents
Although substantial progress has been made toward biodegrading
other CW agents, treating the arsenic-containing agents such as adamsite,
lewisite, and mustard-lewisite mixtures is problematic because
arsenic is toxic. To overcome this problem, Alexander Boronin and his
colleagues at the Institute of Biochemistry and Physiology of Microorganisms
in Pushchino, Russia developed a three-stage, laboratory-scale process
for destroying arsenic-containing CW agents.
For example, their process for treating lewisite entails
initial hydrolysis to form 2-chlorovinyl arsine oxide (CAO). Because
the remaining high arsenic inhibits further biodegradation, they treat
the mixture by electrolysis and electrocoagulation (EC), yielding formate,
acetate, and arsenous and arsenic acids; subsequently, during the EC
step, arsenic precipitates from solution, reducing its concentration
by four orders of magnitude. The remaining organic acids are mineralized
in a fluidized bed reactor using a natural consortium of microorganisms
immobilized on activated carbon. A similar approach is also effective
in destroying mustard-lewisite mixture (MLM) and adamsite, according
to Boronin.
Destroying the arsenic-containing CW agents in the Russian
stockpile will generate thousands of tons of arsenic. Although this
material might prove useful in the microelectronics, optics, and solar
power industries, safe storage facilities are needed. Victor Petrov
and coworkers at the Russian Institute of Applied Mechanics suggest
that converting free arsenic into arsenic sulfide provides a means for
safely storing this bulk material.
Unanswered CW Degradation
Questions Require Further Research
Despite the progress in developing procedures for destroying
CW agents, significant gaps in our knowledge of these compounds limit
development of alternative technologies and slow progress on destroying
them, according to Joseph Bunnett, an organic chemist at the University
of California at Santa Cruz, who has served on a variety of international
scientific panels examining CW agent destruction. For example, in 1982,
officials in the U.S. Army identified incineration as the best technology
to use for this purpose, he points out. Yet, 16 years later, complete
reliance on this incineration-based "chemical demilitarization"
program has resulted in little destruction of agents and remains stymied
because of strong political opposition to incineration.
Citizen opposition to incineration stems in part from
a widely held belief that small amounts of intact chemical warfare (CW)
agents will be released to accumulate as a "toxic load" in
the environment. However, although traces of CW agents released into
the atmosphere are likely to be rapidly destroyed by photolysis, hydrolysis,
and oxidation, little if any research has been done to document the
atmospheric half-lives of most CW agents, according to Bunnett.
Several major CW munitions stockpiles need to be destroyed:
the Russian stockpile, most of the U.S. stockpile, the Japanese CW munitions
abandoned in China in 1945, and the German munitions that were dumped
into the Baltic Sea. Although biodegradation could play a role in destroying
these chemical agents, both fundamental and practical questions need
to be addressed before even successful laboratory-scale degradative
processes can be taken into field-scale use. Yet, unless the pace of
research accelerates to meet the deadlines specified by the Chemical
Weapons Convention, current gaps in knowledge will sharply limit any
use of this promising technology.
Two critical questions need to be addressed soon. One
is how well laboratory-scale procedures will perform under field conditions,
particularly in settings where partly degraded materials contain a mix
of chemical contaminants, as well as an ill-defined range of indigenous
microorganisms. Researchers, who typically have tested their processes
only on highly purified starting materials, will need access to CW agents
from munition stockpiles to see if biodegradative processes will work
on complex mixtures.
A second, more fundamental question to address is whether
new microbial consortia can be selected or developed that are better
suited for carrying out biodegradation of CW agents. One research approach
will be to conduct a comprehensive screening of organisms from anaerobic
sites or from highly acidic, hypersaline, or metal-contaminated aerobic
environments.
In conducting this research, it is crucial that international
collaborative efforts be continued and expanded. Although individual
nations naturally have a domestic focus when deciding on national research
priorities, chemical weapons are an international legacy, and their
inappropriate disposal by any nation may have long-lasting consequences.
By sharing ideas and resources, the international community stands the
best chance of developing and implementing appropriate technology worldwide
to prevent further contamination by these dangerous compounds.
Acknowledgments
The IUPAC Ad Hoc Committee on Chemical Weapons Destruction
Technologies sponsored this review. We gratefully acknowledge NATO for
funding Russian-American linkage grants and for funding the Advanced
Research Workshop on Chemical and Biological Technologies for the Detection,
Destruction, and Decontamination of Chemical Warfare Agents (12-15
May 1996, Russia). We thank Dr. Steve Harvey for his careful reading
of the manuscript and Dr. Joe DeFrank for his suggestions and for calculating
the values shown in Table 1.
Suggested Reading
Cheng, T.C., L. Liu, B. Wang, J. Wu, J. J. DeFrank, D.
M. Anderson, V. K. Rastogi, and A. B. Hamilton. 1997. Nucleotide sequence
of a gene encoding an organophosphorus nerve agentdegrading enzyme from
Alteromonas haloplanktis. J. Ind. Microbiol. Biotechnol. 18:49-55.
DeFrank, J. J., and T.C. Cheng. 1991. Purification and
properties of an organophosphorus acid anhydrolase from a halophilic
bacterial isolate. J. Bacteriol. 173:1938-1943.
Harvey, S. P., L. L. Szafraniec, W. T. Beaudry, D. K.
Rohrbaugh, M. V. Haley, and C. W. Kurnas. 1997. Sequencing batch reactor
biodegradation of HT: a detailed comparison of the results of two different
approaches. U.S. Army Armament Munitions Chemical Command. ERDECTR,
in press.
Kolakowski, J. E., J. J. DeFrank, S. P. Harvey, L. L.
Szafraniec, W. T. Beaudry, K. Lai, and J. R. Wild. 1997. Enzymatic hydrolysis
of the chemical warfare agent VX and its neurotoxic analogues by organophosphorus
hydrolase. Biocatal. Biotransform. 15:297-312.
NATO, Scientific and Environmental Affairs Division. Abstracts
of the advanced research workshop on chemical and biological technologies
for the detection, destruction, and decontamination of chemical warfare
agents (May 12-15, 1996, Russia).
Rainina, E., J.W. Kim, E. Efremenko, C. R. Engler, and
J. R. Wild. 1997. Degradation of thiodiglycol, the hydrolysis product
of sulfur mustard, with bacteria immobilized within poly(vinyl) alcohol
cryogel. Biotechnol. Lett., in press.
U.S. Congress, Office of Technology Assessment. Disposal
of chemical weapons: alternative technologiesbackground paper, OTABP095,
June 1992. U.S. Government Printing Office, Washington, D.C.
U.S. General Accounting Office. Chemical weapons disposal:
plans for nonstockpile chemical warfare materiel can be improved, GAO/NSIAD9555,
Dec. 1994. U.S. Government Printing Office, Washington, D.C.
U.S. General Accounting Office. Chemical weapons and materiel:
key factors affecting disposal costs and schedule, GAO/NSIAD9718, Feb.
1997. U.S. Government Printing Office, Washington, D.C.
Yang, Y.C., L. L. Szafraniec, W. T. Beaudry, and J. R.
Ward. 1988. Kinetics and mechanism of the hydrolysis of 2chloroethyl
sulfides. J. Org. Chem. 53:3293-3297.