Organic Bromine and Iodine Compounds docx

Preface
Environmental Chemistry is a relatively young science. Interest in this subject,
however,is growing very rapidly and, although no agreement has been reached
as yet about the exact content and limits of this interdisciplinary discipline,there
appears to be increasing interest in seeing environmental topics which are based
on chemistry embodied in this subject. One of the first objectives of Environ-
mental Chemistry must be the study of the environment and of natural chemical
processes which occur in the environment. A major purpose of this series on
Environmental Chemistry, therefore, is to present a reasonably uniform view of
various aspects of the chemistry of the environment and chemical reactions
occurring in the environment.
The industrial activities of man have given a new dimension to Environ-
mental Chemistry. We have now synthesized and described over five million
chemical compounds and chemical industry produces about hundred and fifty
million tons of synthetic chemicals annually. We ship billions of tons of oil per
year and through mining operations and other geophysical modifications, large
quantities of inorganic and organic materials are released from their natural
deposits. Cities and metropolitan areas of up to 15 million inhabitants produce
large quantities of waste in relatively small and confined areas. Much of the
chemical products and waste products of modern society are released into the
environment either during production, storage, transport, use or ultimate
disposal. These released materials participate in natural cycles and reactions
and frequently lead to interference and disturbance of natural systems.
Environmental Chemistry is concerned with reactions in the environment.It
is about distribution and equilibria between environmental compartments.
It is about reactions, pathways, thermodynamics and kinetics. An important
purpose of this Handbook, is to aid understanding of the basic distribution and
chemical reaction processes which occur in the environment.
Laws regulating toxic substances in various countries are designed to assess
and control risk of chemicals to man and his environment. Science can con-

tribute in two areas to this assessment; firstly in the area of toxicology and
secondly in the area of chemical exposure. The available concentration
(“environmental exposure concentration”) depends on the fate of chemical
compounds in the environment and thus their distribution and reaction be-
haviour in the environment.One very important contribution of Environmental
Chemistry to the above mentioned toxic substances laws is to develop laboratory
test methods, or mathematical correlations and models that predict the environ-
mental fate of new chemical compounds.The third purpose of this Handbook is
to help in the basic understanding and development of such test methods and
models.
The last explicit purpose of the Handbook is to present, in concise form, the
most important properties relating to environmental chemistry and hazard
assessment for the most important series of chemical compounds.
At the moment three volumes of the Handbook are planned.Volume 1 deals
with the natural environment and the biogeochemical cycles therein, including
some background information such as energetics and ecology.Volume 2 is con-
cerned with reactions and processes in the environment and deals with physical
factors such as transport and adsorption, and chemical, photochemical and
biochemical reactions in the environment, as well as some aspects of pharma-
cokinetics and metabolism within organisms.Volume 3 deals with anthropogenic
compounds, their chemical backgrounds, production methods and information
about their use, their environmental behaviour, analytical methodology and
some important aspects of their toxic effects. The material for volume 1, 2 and 3
was each more than could easily be fitted into a single volume, and for this
reason, as well as for the purpose of rapid publication of available manuscripts,
all three volumes were divided in the parts A and B.Part A of all three volumes is
now being published and the second part of each of these volumes should appear
about six months thereafter. Publisher and editor hope to keep materials of the
volumes one to three up to date and to extend coverage in the subject areas by
publishing further parts in the future. Plans also exist for volumes dealing with

different subject matter such as analysis, chemical technology and toxicology,
and readers are encouraged to offer suggestions and advice as to future editions
of “The Handbook of Environmental Chemistry”.
Most chapters in the Handbook are written to a fairly advanced level and
should be of interest to the graduate student and practising scientist.I also hope
that the subject matter treated will be of interest to people outside chemistry and
to scientists in industry as well as government and regulatory bodies. It would
be very satisfying for me to see the books used as a basis for developing graduate
courses in Environmental Chemistry.
Due to the breadth of the subject matter, it was not easy to edit this Hand-
book. Specialists had to be found in quite different areas of science who were
willing to contribute a chapter within the prescribed schedule. It is with great
satisfaction that I thank all 52 authors from 8 countries for their understanding
and for devoting their time to this effort. Special thanks are due to Dr.F.Boschke
of Springer for his advice and discussions throughout all stages of preparation
of the Handbook. Mrs. A. Heinrich of Springer has significantly contributed to
the technical development of the book through her conscientious and efficient
work. Finally I like to thank my family, students and colleagues for being so
patient with me during several critical phases of preparation for the Handbook,
and to some colleagues and the secretaries for technical help.
I consider it a privilege to see my chosen subject grow.My interest in Environ-
mental Chemistry dates back to my early college days in Vienna. I received
significant impulses during my postdoctoral period at the University of California
and my interest slowly developed during my time with the National Research
VIII
Preface
Council of Canada, before I could devote my full time of Environmental
Chemistry, here in Amsterdam. I hope this Handbook may help deepen the
interest of other scientists in this subject.
Amsterdam, May 1980 O. Hutzinger

Twentyone years have now passed since the appearance of the first volumes of
the Handbook.Although the basic concept has remained the same changes and
adjustments were necessary.
Some years ago publishers and editors agreed to expand the Handbook by
two new open-end volume series: Air Pollution and Water Pollution. These
broad topics could not be fitted easily into the headings of the first three vol-
umes.All five volume series are integrated through the choice of topics and by a
system of cross referencing.
The outline of the Handbook is thus as follows:
1. The Natural Environment and the Biochemical Cycles,
2. Reaction and Processes,
3. Anthropogenic Compounds,
4. Air Pollution,
5. Water Pollution.
Rapid developments in Environmental Chemistry and the increasing breadth of
the subject matter covered made it necessary to establish volume-editors. Each
subject is now supervised by specialists in their respective fields.
A recent development is the accessibility of all new volumes of the Handbook
from 1990 onwards,available via the Springer Homepage
or or series/hec/.
During the last 5 to 10 years there was a growing tendency to include subject
matters of societal relevance into a broad view of Environmental Chemistry.
To p ics include LCA (Life Cycle Analysis), Environmental Management, Sustain-
able Development and others.Whilst these topics are of great importance for the
development and acceptance of Environmental Chemistry Publishers and Edi-
tors have decided to keep the Handbook essentially a source of information on
“hard sciences”.
With books in press and in preparation we have now well over 40 volumes
available.Authors,volume-editors and editor-in-chief are rewarded by the broad
acceptance of the “Handbook”in the scientific community.

Bayreuth, July 2001 Otto Hutzinger
Preface IX
Introduction
Except for astatine whose chemistry is largely unknown,fluorine and iodine are
the first and last of the halogens. This is shown in a number of ways including
the successive decrease in the redox potential Hal
–
/Hal
2
and the electronegativi-
ty,and increase in the covalent and van der Waals radii. The substitution of
hydrogen by fluorine does not greatly alter the structure of organofluorines in
contrast to the effect of introducing bulky bromine or iodine substituents.
Although fluorides are found abundantly in a range of minerals, the taming of
both elemental fluorine and the hydrogen fluorides presented serious experi-
mental difficulties that were solved only after many years of dangerous work and
were a prelude to the synthesis of organofluorines.Bromide is present in seawa-
ter at a concentration of 65 ppm and iodide at 0.05 ppm although these concen-
trations are greatly exceeded in hypersaline lakes that are the current source of
bromide and iodide.
The preparation of both elemental bromine and iodine was accomplished
more than 60 years before that of elemental fluorine, bromine in 1826 and iodi-
ne in 1811’ and the synthesis of organobromine and organoiodine compounds
presented fewer problems. A wide range of organofluorines has achieved in-
dustrial importance as refrigerants, surfactants, pharmaceuticals, dyestuffs,
whereas the range of organobromine and organoiodine compounds in general
use is much more limited.
Organofluorine compounds exist only in the monovalent state whereas all the
other halogens may exist at oxidation levels up to 7. Organoiodine compounds
may exist in the trivalent and pentavalent states that have seen numerous appli-

cations: they have been used extensively in organic synthesis as oxidizing agents
[Zhdankin and Stang 2002], benziodoxoles have attracted attention as synthetic
reagents for the destruction of chemical weapons [Morales-Rojas and Moss
2002] and iodonium salts have been used to develop a silver-free, single-sheet
imaging medium [Marshall et al. 2002].
The number of naturally occurring organofluorines is structurally limited
and essentially confined to higher plants in contrast to the plethora of organob-
romine – and to a lesser extent organoiodine – metabolites produced mostly by
marine biota. Iodide is essential for many biota including humans, and organic
compounds of iodine have long attracted interest as a result of the physiological
importance of iodinated tyrosines in thyroid function and the antiseptic pro-
perty of diiodine released from triiodomethane.More recently they have achiev-
ed importance as X-ray contrast agents.
Organic compounds of bromine have a greater diversity of application.
Dibromoethane was once used extensively in automobile fuel containing tetrae-
thyl lead to diminish engine corrosion,while methyl bromide has a long history
of use as fumigant and has attracted attention as a result of concern with global
warming and ozone depletion. In addition, oxidants produced in the bromine
cycle in the troposphere have been shown to be important in mobilizing ele-
mentary Hg to species that are both accessible to biota and accumulate in Arctic
snow [Lindberg et al. 2002]. Polybrominated aromatic compounds, and especi-
ally diphenyl ethers,have been used as flame-retardants and are now widely dis-
tributed in the environment.A relatively small number of agrochemicals inclu-
ding bromoxynil, bromacil and bromethuron have been used.
This volume addresses a broad spectrum of the environmental issues surro-
unding organic bromine and iodine compounds. In assessing their environ-
mental significance it is important to assess their partition among the environ-
mental compartments and the potential for their long-range dissemination:
these issues are discussed by Cousins and Palm. Orlando discusses atmospheric
chemistry in the context of ozone depletion and global warming, and the signi-

ficant difference between the reactions of methyl bromide and methyl iodide are
underscored.
Mammalian toxicity is discussed by DePierre and the mechanisms of their
degradation and transformation by Allard and Neilson. There has been consid-
erable interest in naturally occurring metabolites in the current debate on the
fate and partition of methyl bromide that is – or possibly by the time this is
published was – important nematocide and is produced in substantial quantities
as a metabolite of marine algae. There has also been speculation on the natu-
ral occurrence of diphenyl ethers and Neilson discusses plausible mechanisms
for the biosynthesis of representative organic bromine and organic iodine me-
tabolites.
Once again, it is a particular pleasure to thank the authors who were prepar-
ed to sacrifice their valuable time and take on the additional burden of making
their contributions. This is particularly appreciated since, in these days of con-
tinual stress, potential contributors feel themselves already overburdened with
the demands of seeking financial support and producing publications to justify
their existence.Any success with this volume is entirely due to the contributors,
and I feel sure that their effort has been well rewarded in producing an exciting
volume.
Lindberg SE, S Brooks, C-J Lin, KJ Scott, MS Landis, RK Stevens, M Goodsite and A Richter
(2002) Dynamic oxidation of gaseous mercury in the Arctic troposphere at polar sunrise.
Environ Sci Technol 36:1245–1256
Marshall JL, SJ Telfer,MA Young,EP Lindholm,RA Minns,L Takiff (2002) A silver-free,single-
sheet imaging medium based on acid amplification. Science 297:1516-1521
Morales-Royas H and RA Moss (2002) Phosphorolytic reactivity of o-iodosylcarboxylates and
related nucleophiles. Chem Rev 102:2497–2521
Zdankin VV and PJ Stang (2002) Recent developments in the chemistry of polyvalent iodine
compounds. Chem Rev 102:2523–2584
Stockholm, July 2003 Alasdair H. Neilson
XIV

Introduction
Degradation and Transformation of Organic Bromine
and Iodine Compounds: Comparison with their
Chlorinated Analogues
Ann-Sofie Allard
1
· Alasdair H. Neilson
2
Swedish Environmental Research Institute Limited IVL,Sweden
1
E-mail:
2
E-mail:
An overview is given of the pathways for the degradation and transformation of selected
brominated and iodinated aliphatic and aromatic compounds. Although greater emphasis is
placed on reactions mediated by microorganisms,examples of important abiotic reactions are
also given.A mechanistic outline of the enzymology is provided when possible and compar-
isons are made with the chlorinated analogues which have been more extensively studied.
Keywords. Biodegradation and biotransformation, Abiotic transformation, Aliphatic com-
pounds,Aromatic compounds
1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2Aliphatic Compounds . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Halogenated Methanes . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1 Methyl Halides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1.1 Methane Monooxygenase Pathway . . . . . . . . . . . . . . . . . 6
2.1.1.2 Methyl Transfer and Corrinoid Pathways . . . . . . . . . . . . . . 8
2.1.1.3 Corrinoid Transmethylations in Aerobic and Anaerobic
Metabolism of Methyl Halides . . . . . . . . . . . . . . . . . . . . 9
2.1.2 Di- and Trihalomethanes . . . . . . . . . . . . . . . . . . . . . . 12
2.1.2.1 Aerobic Organisms . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.1.2.2 Anaerobic Organisms . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Halogenated Alkanes and Related Compounds with Two or More
Carbon Atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 Halogenated Ethenes . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4 Haloalkanols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5 Haloaldehydes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.6 Haloalkanoates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.7 Halogenated Ethers . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.8 Reductive Loss of Halogen . . . . . . . . . . . . . . . . . . . . . 27
2.9 Brominated and Iodinated Alkanes and Related Compounds
as Metabolic Inhibitors . . . . . . . . . . . . . . . . . . . . . . . 30
3Abiotic Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.1 Photohydrolytic Reactions . . . . . . . . . . . . . . . . . . . . . 31
3.2 Reductive Reactions . . . . . . . . . . . . . . . . . . . . . . . . . 32
© Springer-Verlag Berlin Heidelberg 2003
The Handbook of Environmental Chemistry Vol. 3, Part R (2003): 1–74
DOI 10.1007/b11447HAPTER 1
4Aromatic Compounds : Aerobic Reactions . . . . . . . . . . . . . 34
4.1 Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.1.1 Degradation and Growth . . . . . . . . . . . . . . . . . . . . . . 34
4.1.2 Metabolism Without Growth . . . . . . . . . . . . . . . . . . . . 35
4.1.3 Biotransformation to Dihydrodiols . . . . . . . . . . . . . . . . . 39
4.2 Benzoates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2.1 Dioxygenation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2.1.1 Dehalogenation of 2-Halogenated Benzoates . . . . . . . . . . . . 41
4.2.1.2 Loss of Halogen in 4-Halogenated Phenylacetates . . . . . . . . . 43
4.2.1.3 Halohydrolases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.1.4 Reductive Dehalogenation . . . . . . . . . . . . . . . . . . . . . . 45
4.2.1.5 Denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2.1.6 Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.3 Phenols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.3.1 O-Methylation of Halogenated Phenols . . . . . . . . . . . . . . . 48
4.3.2 Fungal Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.4 Amines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5Alternative Mechanisms of Dehalogenation . . . . . . . . . . . . 51
5.1 Peroxidase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.2 Dehalogenation by a Polychaete . . . . . . . . . . . . . . . . . . . 51
5.3 Dehalogenation by Thymidylate Synthetase . . . . . . . . . . . . 51
6Anaerobic Reactions . . . . . . . . . . . . . . . . . . . . . . . . . 52
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
6.2 Halogenated Hydrocarbons . . . . . . . . . . . . . . . . . . . . . 54
6.2.1 Polyhalogenated Benzenes . . . . . . . . . . . . . . . . . . . . . 54
6.2.2 PCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.2.3 PBBs and Diphenylmethanes . . . . . . . . . . . . . . . . . . . . 56
6.3 Anaerobic Degradation of Benzoates . . . . . . . . . . . . . . . . 59
6.3.1 Dehalogenation . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.3.2 Oxidation and Reduction of Aromatic Carboxylates and
Aldehydes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.4 Phenols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
7Concluding Comments . . . . . . . . . . . . . . . . . . . . . . . 61
8References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
1
Introduction
In the course of preparing this chapter it became evident that relatively few stud-
ies were directed primarily to brominated compounds. Many were concerned
with chlorinated compounds,and some brominated analogues were fortuitously
included. It was therefore necessary to glean the literature on chlorinated com-
2 A S.Allard · A. H. Neilson
pounds and extract details on their brominated and iodinated analogues that
were sometimes included.It was then decided to include results for selected chlo-

rinated compounds for several reasons: (i) for comparison with their brominated
analogues; (ii) when studies of the brominated compounds were lacking and had
been carried out only with the chlorinated analogues; (iii) when studies only with
chlorinated analogues illustrated important principles of metabolism.
Attention is drawn to a selection of reviews that cover various aspects of de-
halogenation [23, 53, 55,84,94, 162, 188,226].
Three different metabolic situations have been encountered: (i) growth at the
expense solely of the brominated compound; (ii) loss of bromide during incu-
bation with cell suspensions or enzymes; (iii) inclusion of a brominated substrate
in the course of enzymological studies. It is worth noting that for some halo-
genated substrates, evidence for diminution of its concentration has been
demonstrated in spite of the absence of dehalogenation.This may plausibly be at-
tributed to simple biotransformations such as oxidation or dehydrogenation un-
der aerobic conditions.
It is important to note the different experimental procedures that have been
used.Experiments under anaerobic conditions have been carried out under a va-
riety of conditions using: (i) pure cultures; (ii) metabolically stable mixtures of
organisms; (iii) unselected suspensions of soil or sediment. The last can lead to
problems in interpretation since the sample used for assay will generally contain
some of the putative degradation products.
A cardinal issue that not been addressed here is the accessibility of brominated
compounds – especially hydrocarbons and phenolic compounds – to the appro-
priate organisms in suspended matter or in the sediment phase containing or-
ganic carbon. This is only noted parenthetically with references to some repre-
sentative illustrations from the relevant literature from chlorinated analogues.
Attention is drawn in the text to some taxonomic changes.For simplicity,these
synonymies are duplicated in the table below.
Previous name Current name
Alcaligenes eutrophus Ralstonia eutropha
Flavobacterium sp. Sphingomonas chlorophenolica

Hyphomicrobium sp.strain CM2 Hyphomicrobium chloromethanicum
Methylobacterium sp.strain CM4 Methylobacterium chloromethanicum
Pseudomonas cepacia Burkolderia cepacia
Pseudomonas paucimobilis Sphingomonaspaucimobilis
Pseudomonas pickettii Ralstonia pickettii
Rhodococcus chlorophenolicum Mycobacterium chlorophenolicum
Clostridium thermoautotrophica Moorella thermoautotrophica
Enterobacter agglomerans Pantoea agglomerans
For chlorinated compounds, the greatest attention has been given to groups of
substances that are considered environmentally unacceptable, for example, low
Degradation and Transformation of Organic Bromine and Iodine Compounds 3
molecular mass chlorinated aliphatic compounds used as solvents,chiral chloro-
propionates incorporated into agrochemicals,hexachlorocyclohexane,PCBs,and
pentachlorophenol used as a wood preservative. Although brominated organic
compounds are important as agrochemicals, pharmaceuticals and flame-retar-
dants,and iodinated compounds as X-ray contrast agents,these have been stud-
ied less exhaustively than their chlorinated analogues. In addition, the appro-
priate compounds may not be commercially available as substrates and it may
seem unusually academic to synthesize them.
Reliance has of necessity been placed on the metabolism of chlorinated com-
pounds, particularly for the structures of those enzymes that have been deter-
mined by X-ray analysis.Greatest weight has been placed on studies in which the
biochemistry of degradation and transformation has been elucidated, and in
which comparison among the halogens is possible.
There have been major methodological developments during recent years.
These include the success in obtaining crystals of enzymes that enable the ap-
plication of X-ray analysis to the study of enzyme mechanisms: these provide im-
portant details and where available the results of such studies have been included.
Although
13

C NMR has been used generally with cell suspensions, the availabil-
ity of on-line LC-NMR opens this to wider application in establishing the struc-
ture of transient metabolites.There have been substantial advances in establish-
ing the genetics of degradation, and procedures for comparing amino acid and
nucleotide sequences among groups of enzymes. This has made it possible to es-
tablish relationships between enzymes from different organisms and encouraged
speculation on their evolution.This aspect has not,however,been treated here in
the depth that it deserves.
It is worth noting that – with the exception of simple bromophenols – virtu-
ally no investigations have been directed to the biodegradation of the plethora
of naturally occurring brominated organic compounds that are discussed by
Neilson.
2
Aliphatic Compounds
Introduction
A number of brominated alkanes including methyl bromide,1,2-dibromoethane,
1,2-dibromoethene,and propargyl bromide have been used in agriculture as fu-
migants and nematicides. Concern for the adverse effect of these on the de-
struction of ozone and the long half-life of methyl bromide has resulted in stud-
ies on their microbial degradation, as well as attempts to quantify their natural
production and the extent to which the ocean serves as a sink. This is discussed
in the chapter by Cairns and Palm and, on the basis of the “replacement prin-
ciple”,attention has been redirected to the use of propargyl bromide [248].Poly-
chlorinated ethanes and ethenes have been extensively used as solvent and de-
greasing agents in the metallurgical industry and concern has arisen over their
adverse health effects.This has stimulated efforts to study their degradability and
4 A S.Allard · A. H. Neilson
to find replacements: indeed this applies equally to all polyhalogenated aliphatic
compounds.
An outline of the primary C-Br fission reactions encountered during the

degradation of brominated alkanes, alkenes, brominated alkanols and bro-
moalkanoates is given in Fig. 1. Further reactions are, of course, possible, when
reactive intermediates such as epoxides or ethenes are formed.
Degradation and Transformation of Organic Bromine and Iodine Compounds 5
Fig. 1. Outline of primary reactions involved in degradation or transformation of haloalkanes
and related compounds
2.1
Halogenated Methanes
2.1.1
Methyl Halides
A Taxonomic Note –To avoid possible confusion,taxonomic changes in this area
[128] are given:
Methylobacterium sp.strain CM4 Æ Methylobacterium chloromethanicum
Hyphomicrobium sp.strain CM2 Æ Hyphomicrobium chloromethanicum
together with the names of other organisms that are discussed:
Leisingeria methylhalidovorans
Methylobacterium extorquens
Degradation in the Natural Environment. It has been established that the
biodegradation of methyl bromide occurs in a number of natural environments.
For example, a methylotrophic bacterium IMB-1 isolated from agricultural soil
was able to degrade methyl bromide to CO
2
[75].The degradation of methyl bro-
mide in a mixed soil bacterial flora occurred at concentrations several powers of
ten lower than have been used in previous experiments (ten parts per billion by
volume) [82]. At these low concentrations, neither chemical degradation nor
anaerobic degradation occurred. This potential has been examined in freshwa-
ter, estuarine, and seawater samples in which non-bacterial degradation was
eliminated from the results by lack of inhibition of degradation by methyl fluo-
ride: both methyl bromide and methylene dibromide were examined but only in

the freshwater sample was degradation observed [68]. Two strains were able to
degrade methyl bromide at concentrations of the mixing ratio of tropospheric
methyl bromide with surface water and displayed no evidence of a threshold con-
centration for uptake [70].Both strains IMB-1 and Leisingeria methylohalidovo-
rans strain MB2 degrade methyl bromide by respiration that is mediated by a
methyltransferase whereas in Methylomonas rubra that is also able to take up
methyl bromide at comparably low concentrations degradation of the substrates
is mediated by a monooxygenase.
Strains Involved in Degradation. There are two distinct mechanisms for the
degradation of halomethanes involving (1) methane monooxygenase and (2) cor-
rin-dependent, and the biodegradation of methyl bromide has been demon-
strated in both groups.
2.1.1.1
Methane Monooxygenase Pathway
A number of strains with monooxygenase activity have been examined and
it is convenient to add some comment on the enzyme since various types of met-
hane monooxygenase have played important roles in the degradation of halo-
6 A S.Allard · A. H. Neilson
genated aliphatic compounds. The enzyme exists in both a soluble and a par-
ticulate form of which the former has been more extensively studied. The
enzyme consist of three components: a hydroxylase, a regulatory protein that
is not directly involved in electron transfer between the hydroxylase,and a third
protein that is a reductase containing FAD and an [2Fe-2S] cluster. Details of
the structure of the hydroxylase and the mechanism of its action involving
the Fe
III
-O-Fe
III
at the active site are given in a review [112]. The particulate
enzyme contains copper or both copper and iron, and the concentration of

copper determines the catalytic activity of the enzyme [194]. For example,
trichloroethene is degraded by Methylosinus trichosporium strain OB3b under
copper limitation when the soluble monooxygenase is formed, but not during
grown with copper sufficiency when the particulate form is synthesized [152].
Examples of methyl bromide-degrading strains include the following:
1. The soluble methane monooxygenase from Methylococcus capsulatus (Bath)
is able to oxidize chloro- and bromomethane, but not iodomethane with the
presumptive formation of formaldehyde [36].
2. The methane degrading Methylosinus trichosporium OB3b has been shown to
degrade both methyl bromide and dibromomethane [9, 196] and the
propane-degrading Mycobacterium vaccae JOB5 methyl bromide (Table 1)
[196].The degradation pathway for Methylosinus trichosporium OB3b was ex-
amined in an elegant study using
13
C NMR with [
13
C]CH
3
Br and [
13
C]CH
2
Br
2
as substrates.Although the expected formaldehyde from the former could not
be demonstrated possibly on account of its rapid further transformation,the
formation of CO was shown for CH
2
Br
2

by
13
C NMR, and the involvement of
methane monooxygenase was supported by inhibition of activity by acety-
lene [9]. Although it was postulated that the initial reactions were monoxy-
genation followed by loss of hydrogen bromide, more recent studies on the
metabolism of both methyl chloride and methyl bromide show that the
reactions are corrinoid-dependent (see below). It is also worth noting the
contrasting mechanisms for the degradation of methyl chloride and
dichloromethane. One of the fascinating results of the studies with methyl
chloride is the similarity of pathways proposed for aerobic and strictly anaer-
obic bacteria.
3. Suspensions of Nitrosomonas europaea were able to oxidize a number of halo-
genated alkanes more effectively in the presence of NH
4
+
that was oxidized to
nitrite (Table 2) [221].
Degradation and Transformation of Organic Bromine and Iodine Compounds 7
Table 1. Concentrations of bromide (µmol) in cultures in which the substrates hadbeen de-
graded. The theoretical values are 4.5 for methyl bromide and 11 for dibromoethane [196]
Organism Methyl bromide Dibromoethane
Methylosinus trichosporium OB3b 4.5 9.2
Strain ENV 2041 5.3 14.1
Mycobacterium vaccae JOB5 3.0 NA
NA = not available.
2.1.1.2
Methyl Transfer and Corrinoid Pathways
This pathway is used by a number of organisms, and a general outline is given:
1. Strain IMB-1 is able to grow at the expense of methyl bromide [239] and

belongs to a group of organisms that are also able to degrade methyl io-
dide but unable to use formaldehyde or methanol [176].A single gene clus-
ter contained six open reading frames: cmuC, cmuA, orf 146, paaE, hutI,and
part of metF.Although CmuA from this strain had a high homology with the
methyl transfer of Methylobacterium chloromethanicum and Hyphomi-
crobium chloromethanicum,CmuB that has been identified in these strains
was not detected. A study with Hyphomicrobium chloromethanicum strain
CM2 revealed a cmu gene cluster containing ten open reading frames:
folD (partial), pduX, orf153, orf 207, orf 225, cmuB, cmuC, cmuA, fmdB,
and paaE (partial). CmuA, CmuB, and CmuC from this strain showed a
high similarity to those from Methylobacterium chloromethanicum (Table 3)
[239] and it was postulated that the pathway for chloromethane degradation
in this strain was similar to that in Methylobacterium chloromethanicum
[126].
2. Methylobacterium sp.CM4 [222, 223] is able to degrade methyl chloride, and
details of the metabolism by this strain (now classified as Methylobacterium
chloromethanicum) have been resolved and are discussed below.
8 A S.Allard · A. H. Neilson
Table 2. Loss of haloalkanes by Nitrosomonaseuropaea during oxidation of NH
4
+
.Substrate
remaining after 24 h as % of the initial amount [222]
Substrate Remaining Substrate Remaining
substrate % substrate %
Dichloromethane 0 1,2-Dibromoethane 16
Dibromomethane 4 trans-Dichloroethene 25
Bromoethane 25 trans-Dibromoethene 100
cis-Dichloroethene 9
cis-Dibromoethene 3

Table 3. Summary of Hyphomicrobium chloromethanicum methyltransferase genes and iden-
tity (%) with representative proteins [239]
Gene Inferred function Sequence comparison (% identity)
FolD Methylene tetrahydrofolate
Cyclohydrolase/dehydrogenase
CmuB Methyltransferase M. chloromethanicum CM4 cmuB (57)
CmuC Methyltransferase M. chloromethanicum CM4 cmuC (36)
and orf414 (34)
CmuA Methyltransferase and corrinoid M. chloromethanicum CM4 cmuA (80)
protein
PaaE Reductase E. coli PaaE (33), P. pu t id a Tdn (32)
2.1.1.3
Corrinoid Transmethylations in Aerobic and Anaerobic Metabolism of Methyl Halides
The existence of corrinoids in anaerobic bacteria in substantial concentrations
is well established and their metabolic role in acetogenesis and in methanogen-
esis understood. Their involvement in degradation pathways of aerobic organ-
isms is more recent,and it has emerged that their roles under these different con-
ditions are similar. These issues are explored in the following paragraphs with a
view to illustrating the similar metabolic pathways used by both aerobes and
anaerobes.
Corrinoids are involved in aerobic degradation as noted below for the degra-
dation of methyl chloride by the aerobic Methylobacterium sp.strain CM4, and
also C
1
degradation by Methylobacterium extorquens [34]. Methyl corrins are key
components in transmethylation and examples illustrating the similarity of path-
ways in aerobic and anaerobic metabolism will be summarized. In the following
discussion, tetrahydrofolate or tetrahydromethanopterin (Fig. 2) are implicated
in the form of their methyl (CH
3

), methylene (CH
2
), methine (CH), and formyl
(CHO) derivatives (Fig. 3). The formation of a CH
3
-Co bond is integral and gen-
erally the 5,6-dimethylbenziminazole is displaced by histidine.
Aerobic Degradation of Methyl Chloride – Methylotrophic bacteria have been
isolated that are able to use methyl chloride aerobically as the sole source of
energy and carbon. The substrate is metabolized to formaldehyde and under-
goes subsequent oxidation either to formate and CO
2
or incorporation via the
serine pathway.A study using a strain CC495 that is similar to the strain IMB-1
noted above revealed the complexity of this reaction [38] while details had
emerged from a somewhat earlier of methyl chloride degradation by the aero-
bic Methylobacterium sp.strain CM4 (Methylobacterium chloromethanicum).
Cobalamin was necessary for growth with methyl chloride, though not for
growth with methylamine, and use of mutants containing a miniTn5 insertion
Degradation and Transformation of Organic Bromine and Iodine Compounds 9
Fig. 2. Partial structures of tetrahydrofolate (H
4
F) and tetrahydromethanopterin (H
4
MPT)
and enzyme assays revealed the mechanism of the degradation involving initial
methyl transfer to a Co(I) corrinoid followed by oxidation via tetrahydrofolates
to formyltetrahydrofolate and thence to formate with production of ATP (Fig.4)
[222].
Anaerobic Degradation of Methyl Chloride – The anaerobic methylotrophic ho-

moacetogen Acetobacterium dehalogenans is able to grow with methyl chloride
and CO
2
and uses a comparable pathway for dehydrogenation of the methyl
group involving tetrahydrofolate,a corrinoid coenzyme while the activity of CO
dehydrogenase and the methyl tetrahydrofolate produce acetate (Fig. 5) [130].
Some of the gene products are shared with those involved in metabolism of
methyl chloride [222] (Table 4).The methyl transfer reactions and those involved
in the subsequent formation of acetate have been explored for the demethylase
of this strain [101] and also resemble closely those for the aerobic metabolism of
methyl chloride by aerobic methylotrophs.
10 A S.Allard · A. H. Neilson
Fig. 3. Dehydrogenation of CH
3
-tetrahydrofolate to CHO-tetrahydrofolate
Degradation and Transformation of Organic Bromine and Iodine Compounds 11
Fig. 4. Degradation of methyl chloride by Methylobacterium chloromethanicum (Redrawn from
[222])
Fig. 5. Degradation of methyl chloride by Acetobacterium halogenans (Redrawn from [101,
130])
2.1.2
Di- and Trihalomethanes
2.1.2.1
Aerobic Organisms
Several organisms including species of Pseudomonas, Hyphomicrobium,and
Methylobacterium [105] have been shown to utilize dichloromethane,and the de-
halogenases closely resemble each other. The mechanism for dechlorination in-
volves a glutathione S-transferase that produced dideuteroformaldehyde from
dideuterodichloromethane from cell extracts of Hyphomicrobium sp.strain DM2
[72], so that neither elimination-addition nor oxidation-reduction mechanisms

are possible.Cell extracts of this strain were able to dehalogenate a number of di-
halomethanes (Table 5) [197]. There are two different dichloromethane-dehalo-
genating glutathione S-transferases,neither of which contain metals,the enzyme
from Hyphomicrobium sp.strain DM 4 with an
a
6 and that from Methylobac-
terium sp. strain DM 11 with an
a
2 structure [105]. Glutathione S-transferase is
also involved in the degradation of isoprene (2-methyl-buta-1,3-diene) by
Rhodococcus sp.strain AD45 [215] and is able to transform cis- and trans-1.2-
dichlorethene to the epoxides with formation of glyoxal. The enzyme has been
purified [216] and has a wide range of substrate specificity (Table 6).Glutathione
is also involved in the dechlorination of hexachlorocyclohexane catalyzed by
LinD in Sphingomonas paucimobilis strain UT26 [141] and the dehalogenation of
tetrachlorohydroquinone by Flavobacterium sp. [246].
The degradation of dibromo- and tribromomethanes has been examined un-
der different conditions: (a) an enrichment culture from seawater was able to de-
12 A S.Allard · A. H. Neilson
Table 4. Genes, inferred function and identity (%) to representatives [222]
Gene Inferred function Comparison Identity
folD 5,10-Methylene-H
4
folate dehydrogenase/ FolD (E. coli)49
5,10-methenyl-H
4
folate cyclohydrolase
purU 10-Formyl-H
4
folate hydrolase PurU (Corynebacterium sp. 47

cmuA Methyltransferase/corrinoid protein MtbA /Methanosarcina barkeri 24
metF 5,10-Methylene-H
4
folate reductase Orf (Saccharomyces cerevisiae)24
cmuB Methyl transfer MtrH (Methanobacterium
thermoautotrophicum 30
Table 5. Rate of dehalogenation (mKat/mg protein) of dihalogenated methanes by cell extracts
of Hyphomicrobium sp.strain DM 2 [197]
Substrate Rate Substrate Rate
Dichloromethane 3.0 Dibromomethane 2.6
Bromochloromethane 3.3 Diiodomethane 0.8
grade
14
CH
2
Br
2
to
14
CO
2
; (b) degradation was studied in a marine strain of Methy-
lobacter marinus strain A45 and new type I methanotrophic strains designated
KML E-1 and KML E-2: the first was able to degrade methyl bromide and dibro-
momethane whereas the last was able to degrade tribromomethane but not di-
bromomethane [69]. It has been established that strains bearing plasmids for
monooxygenation of toluene are able to dechlorinate chloroform: for example,
the toluene 4-monooxygenase from Pseudomonas mendocina strain KR1 [127],
and the generalized toluene 2-, 3-, and 4-monooxygenase from Pseudomonas
stutzeri strain OX1[32] (halogenated alkenes are discussed elsewhere in this

chapter).
2.1.2.2
Anaerobic Organisms
Acetobacterium dehalogenans is able to degrade dichloromethane and the path-
ways resemble formally that for the anaerobic degradation of methyl chloride
(Fig. 5). A strain of Dehalobacterium formicoaceticum is able to use only
dichloromethane as a source of carbon and energy forming formate and acetate
[138]. The pathway involves initial synthesis of methylene tetrahydrofolate of
which two-thirds is degraded to formate with generation of ATP while the other
third is dehydrogenated, transmethylated, and after incorporation of CO forms
acetate with production of ATP (Fig. 6). The formation of [
13
C]formate,
[
13
C]methanol,and [
13
CH
3
]CO
2
H was elegantly confirmed using a cell suspension
and [
13
C]CH
2
Cl
2
.It was suggested that a sodium-independent F
0

F
1
-type ATP syn-
thase exists in this organism in addition to generation of ATP from formylte-
trahydrofolate.
A strain of Acetobacterium woodii strain DSM 1930 dehalogenated tetra-
chloromethane to dichloromethane as the final chlorinated product, while the
carbon atom of [
14
C]tetrachloromethane was recovered as acetate (39%), CO
2
(13%),and pyruvate (10%) [49].Since the transformation of tetrachloromethane
to chloroform and CO
2
is a non-enzymatic corrinoid-dependent reaction [50,77]
it seems safe to assume operation of the acetyl-CoA synthase reaction and the
synthesis of acetate that also takes place during the degradation of
dichloromethane by Dehalobacterium formicoaceticum and in which the CO
2
originates from the medium [139].
Synthesis of Corrinoid-Dependent Reactions – It is appropriate to bring to-
gether a number of related reactions. These resemble those noted above even
Degradation and Transformation of Organic Bromine and Iodine Compounds 13
Table 6. Substrate specificity of S-glutathione transferase from Rhodococcus sp. strain AD45
(isoprene monoepoxide=100%) [216]
Substrate Activity Substrate Activity
Epoxyethane 37 cis-1,2-Dichloroepoxyethane 4
1,2-Epoxybutane 26 Epifluorohydrin 28
1,2-Epoxyhexane 25 Epichlorohydrin 21
Epibromohydrin 25

though they do not involve halogenated substrates. The metabolism of acetate
and lactate by Desulfomaculatum acetoxidans and Archaeoglobus fulgidus re-
spectively and the pathways are given (Fig. 7), and are clearly essentially iden-
tical to those used for anaerobic degradation of methyl chloride and
dichloromethane. In a wider context methanogenesis by Methanosarcina bark-
eri is worth noting: methane can be synthesized from CO
2
and H
2
,or acetate, or
methanol or methylamine.There are,however,important differences from the re-
actions noted above:
1. Use of tetrahydromethanopterin in place of tetrahydrofolate
2. The involvement of an aminofuran as acceptor of the formate produced from
CO
2
3. The different structure of the corrin that transfers the methyl group to coen-
zyme M and thence to methane
Important details on the structures of the corrinoid reductases may be found in
a review [117].
14 A S.Allard · A. H. Neilson
Fig. 6. Degradation of methylene chloride by Dehalobacterium formicoaceticum (Redrawn
from [138])
2.2
Halogenated Alkanes and Related Compounds with Two or More Carbon Atoms
Alkanes with a Single Halogen Atom – The monooxygenase in ammonia-oxidiz-
ing Nitrosomonas europaea has been examined for oxidation of halogenated
ethanes and resulted in production of acetaldehyde presumably by initial termi-
nal hydroxylation (Table 7) [158] while a strain of Nitrosomonas europaea was
shown to oxidize a number of substrates including dibromoethane, and cis- and

trans-dibromoethene (Table 2) [221].
The rates of dehalogenation of a range of 1-substituted haloalkanes was ex-
amined in an Arthrobacter sp.strain HA1 (Table 8) and the enzyme was a halo-
hydrolase that produced the corresponding alkanol and dehalogenated a much
wider range of substrates than could be used for growth [179]. Further investi-
gations with the same strain confirmed that the reaction was hydrolytic, showed
that there were three dehalogenases,examined the pattern of induction,and ex-
tended the range of growth substrates to 1-brominated alkanes C
10
,C
12
,C
14
,and
C
16
[180]. Pseudomonas sp.strain ES-2 was able to grow with a range of bromi-
Degradation and Transformation of Organic Bromine and Iodine Compounds 15
Fig. 7a,b.
Comparison of degradation of: a acetate by Desulfomaculatum acetoxidans; b lactate
by Archaeoglobus fulgidus (Redrawn from [202a])
nated alkanes that greatly exceeded the range of chlorinated or unsubstituted
alkanes: bromoalkanes with chain lengths of C
6
to C
16
,and C
18
could all be uti-
lized [187].A range of chlorinated, brominated, and iodinated alkanes C

4
to C
16
was incubated with resting cells of Rhodococcus rhodochrous NCIMB 13064 [40],
and dehalogenation assessed from the concentration of halide produced
(Table 9).The range of substrates is impressive and the yields were approximately
equal for chloride and bromide and greater than for iodide.
Possibly more remarkable is the metabolic capacity of species of mycobacte-
ria including the human pathogen Mycobacterium tuberculosis strain H37Rv
[96]. The specific activities in extracts of M. avium and M. smegmatis to a range
of halogenated alkanes is given in Table 10. On the basis of aminoacid and DNA
sequences, the strain that was used contained three halohydrolases and the de-
bromination capability of a selected number of other species of mycobacteria is
given in Table 11. The haloalkane dehalogenase gene from M. avium has been
cloned and partly characterized [97].
16 A S.Allard · A. H. Neilson
Table 7. Rate of formation of acetaldehyde [nmol/min/mg protein] by whole cells of Nitro-
somonas europaea from 1-halogenated ethanes in the presence of 10 mmol/l NH
4
Cl [158]
Substrate (µmol) Rate Substrate (µmol) Rate
Fluoroethane (27) 93 Bromoethane (4,8) 122
Chloroethane (9) 221 Iodoethane (1.1) 19
Table 8. Rates of hydrolysis of 1-haloalkanes in cell extracts of Arthrobacter strain HA1 grown
with 1-chlorobutane=100 [179]
Alkane C
1
C
2
C

3
C
4
C
5
C
6
C
7
C
8
C
9
1-Bromo ND 159 163 78 40 56 98 116 125
1-Iodo 53 148 186 89 58 28 22 ND ND
ND = not determined.
Table 9. Dehalogenation of long-chain alkyl halides by Rhodococcus rhodochrous strain
NCIMB 13064 measured as halide release (1-chlorobutane=100). The symbols in parentheses
designate growth at the expense of the substrate [40]
Substrate Dehalo- Substrate Dehalo- Substrate Dehalo-
genation genation genation
1-Chloro- 1-Bromo- 1-Iodo-
propane 121 (+) propane 112 (+) propane 92 (+)
butane 100 (+) butane 102 (+) butane 30 (+)
octane 43 (+) octane 135 (–)
dodecane 19 (+) dodecane 20 (+) dodecane 21 (+)
hexadecane 5 (+) hexadecane 15 (+)
octadecane 0 (+) octadecane 8 (+) octadecane 0 (+)
Degradation and Transformation of Organic Bromine and Iodine Compounds 17
Table 10. Relative specific activity (µmol alkanol produced/mg protein/min) of extracts of

Mycobacterium avium MU1 and M. smegmatis CCM 4622 to halogenated alkanes [96]
Substrate Product M. avium M. smegmatis
1-Bromopropane Propan-1-ol 0.87 3.58
1,3-Dibromopropane 3-Bromo-propan-1-ol 1.23 2.50
1-Chlorobutane Butan-1-ol 0.11 0.42
1-Bromobutane Butan-1-ol 0.66 1.12
1-Chlorohexane Hexan-1-ol 1.02 2.62
1-Bromohexane Hexan-1-ol 0.77 0.91
1-Iodohexane Hexan-1-ol 1.38 3.32
Table 11. Specific activity (µmol bromide produced/mg protein/min) of dehalogenase from
selected species of Mycobacterium towards 1,2-dibromoethane [96]
Ta xon Ac t iv i t y Ta x on Ac t iv i t y
M. bovis BCG MU10 99 M. avium MU1 36
M. fortuitum MU8 76 M. phlei CCM 5639 22
M. triviale MU3 61 M. parafortuitun MU2 22
M. smegmatis CCM4622 49 M. chelonae 20
Table 12. Relative substrate activities (1-chlorobutane (=100) of crude halohydrolase from
Rhodococcus erythropolis Y2 towards
a
,
w
-dihaloalkanes [172]
Substrate Relative activity Substrate Relative activity
1,2-Dichloroethane 6 1,2-Dibromoethane 802
1,3-Dichloropropane 202 1,2-Dibromopropane 132
1,4-Dichlorobutane 232
1,6-Dichlorohexane 168
1,9-Dichlorononane 61
1,10-Dichlorodecane 61
Alkanes with More than a Single Halogen Atom – Some strains are able to use

a
,
w
-dichlorinated alkanes for growth, and the activity of the hydrolase from
Rhodococcus erythropolis strain Y2 was high for 1,2-dibromoethane, 1,2-di-
brompropane, and the
a
,
w
-dichloroalkanes (Table 12) [172] whereas the range
of
a
,
w
-dichlorinated alkanes that was used for growth of Pseudomonas sp.strain
273 was limited to the C
9
and C
10
substrates [238].
Dehalogenase activity was demonstrated in a strain of Acinetobacter GJ70
that could degrade some
a
,
w
-dichloroalkanes, and 1-bromo- and 1-iodopro-
pane.Although 1,2-dibromoethane could be converted to 2-bromoethanol, this
could not be used for growth possibly due to the toxicity of bromoacetaldehyde
and the unsuitability of dihydroxyethane as growth substrate [92]. In a later
study the enzyme from this strain showed dehalogenase activity towards a wide

range of substrates including halogenated alkanes, alkanols and ethers [95]
(Table 13).
It seems valuable to provide a brief summary of the degradation of 1,2-
dichloroethane by Xanthobacter autotrophicus strain GJ10 which has been used
to delineate all stages of the metabolism (Fig.8).The activity of a haloalkane de-
halogenase initiates degradation and is discussed in this section, while the alka-
nol dehydrogenase, the aldehyde dehydrogenase, and the haloacetate dehalo-
genase are discussed in subsequent sections. The enzyme responsible for
dehalogenase activity has been purified from Xanthobacter autotrophicus strain
GJ10,consists of a single polypeptide chain with a molecular mass of 36 kDa, and
was able to dehalogenate chlorinated, and both brominated and iodinated alka-
nes [103]. Details of the mechanism have been explored using an ingenious
method of producing crystal at different stages of the reaction [224]. The over-
all reaction involves a catalytic triad at the active site: Asp
124
binds to one of the
carbon atoms, and hydrolysis with inversion is accomplished by cooperation of
Asp
260
and His
289
with a molecule of water bound to Glu
56
(Fig. 9).In a Mycobac-
terium sp.strain GP1 that belongs to the group of fast-growing mycobacteria,1,2-
dibromoethane could be used as a source of carbon and energy.Although it was
converted into the epoxide by a haloalkane dehalogenase that could be used for
growth and thereby circumvent the production of toxic bromoacetaldehyde,
degradation of the epoxide was unresolved [156].It is worth noting that, in con-
trast,1,2-dichloroethane can be used for growth by Xanthobacter autrotrophicus

strain GJ10: the pathway is shown in Fig. 8, and the appropriate enzymes have
been demonstrated [93].The second step in the degradation of
g
-hexachlorocy-
clohexane by Sphingomonas paucimobilis UT26 is carried out by the hydrolytic
dehalogenation of 1,3,4,6-tetrachlorocyclohexa-1,4-diene to 2,5-dichlorocyclo-
hexa-2,5-diene-1,4-diol [141] and the enzyme is also able to carry out debromi-
nation (Table 14) [142].
Pseudomonas putida strain G786) that harbors the CAM plasmid debromi-
nated some polybrominated ethanes under anaerobic conditions [89],for exam-
ple 1,1,2,2-tetrabromoethane, was reduced to a mixture of cis- and trans-1,2-
dibromoethene that were also formed from 1,2-dichloro-1,2-dibromoethane
(Fig. 10).
18 A S.Allard · A. H. Neilson
Table 13. Rates of dehalogenation with purified dehalogenase from Acinetobacter sp. strain
GJ70 relative to 1-bromopropane (=100) [95]
Halomethane Rate n-Haloalkane Rate Halogenated alkanol Rate
Methyl bromide 143 Bromoethane 143 2-Bromoethanol 55
Methyl iodine 75 Iodoethane 93 3-Bromopropanol 123
Dibromomethane 1-Brompropane 100
1-Iodopropane 66
Fig. 8. Degradation of 1,2-dichloroethane by Xanthobacter autotrophicus strain GJ10 (Redrawn
from [94])
Degradation and Transformation of Organic Bromine and Iodine Compounds 19
Fig. 9. Active site of haloalkane dehalogenase with 1,2-dichloroethane as substrate (Redrawn
from [224])
Table 14. Selected substrates dehalogenated by the dehalogenase (LinB) from Sphingomonas
paucimobilis strain UT26 (chlorobutyrate=100) [142]
SubstrateRelative rate
Bromoethane 257

Chlorobutane 100
Bromobutane 234
1,2-Dibromoethane 355
1,2-Dibromopropane 241
Fig. 10a, b.
Metabolism of: a 1,2-dibromo-1,2-dichloroethane; b tetrabromoethane by
Pseudomonas putida G786 (Redrawn from [89])
(a)
(b)