Methyl Bromide (EHC 166, 1995)

INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

ENVIRONMENTAL HEALTH CRITERIA 166

METHYL BROMIDE

This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.

First draft prepared by Dr. R.F. Hertel and Dr. T. Kielhorn.
Fraunhofer Institute of Toxicology and Aerosol Research,
Hanover, Germany

Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization

World Health Orgnization
Geneva, 1995

The International Programme on Chemical Safety (IPCS) is a
joint venture of the United Nations Environment Programme, the
International Labour Organisation, and the World Health
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toxicology. Other activities carried out by the IPCS include the
development of know-how for coping with chemical accidents,
coordination of laboratory testing and epidemiological studies, and
promotion of research on the mechanisms of the biological action of
chemicals.

WHO Library Cataloguing in Publication Data

Methyl bromide.

(Environmental health criteria ; 166)

1.Hydrocarbons, Brominated - standards 2.Environmental exposure
I.Series

ISBN 92 4 157166 7 (NLM Classification: WA 240)
ISSN 0250-863X

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CONTENTS

1. SUMMARY

1.1. Physical and chemical properties, and analytical
methods
1.2. Sources of human and environmental exposure
1.3. Environmental transport, distribution, and
transformation
1.4. Environmental levels and human exposure
1.5. Kinetics and metabolism
1.6. Effects on organisms in the environment
1.7. Effects on experimental animals
1.8. Effects on humans

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND
ANALYTICAL METHODS

2.1. Identity
2.1.1. Primary constituent
2.1.2. Technical product
2.2. Physical and chemical properties
2.2.1. Physical properties
2.2.2. Chemical properties
2.3. Conversion factors
2.4. Analytical methods
2.4.1. Methyl bromide in air
2.4.2. Methyl bromide in water
2.4.3. Determination of methyl bromide in soil
2.4.4. Methyl bromide in cereal grains and
other foods
2.4.5. Methyl bromide in serum, plasma and blood
and post-mortem tissue
2.4.6. Determination of inorganic bromide in air
2.4.7. Determination of inorganic bromide in water
2.4.8. Determination of inorganic bromide in soils
2.4.9. Determination of inorganic bromide in plant
material/food
2.4.10. Determination of inorganic bromide in
urine, blood/serum/plasma

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1. Natural occurrence
3.2. Anthropogenic sources
3.2.1. Production levels and processes
3.2.1.1 Producers and world production
figures
3.2.1.2 Production processes

3.2.1.3 Losses to the environment during
normal production
3.2.1.4 Methods of transport
3.2.1.5 Accidental release or exposure
3.2.2. Uses
3.2.2.1 Soil fumigation
3.2.2.2 Quarantine and non-quarantine
commodity treatments
3.2.2.3 Structural fumigation
3.2.2.4 Industrial uses
3.2.3. Methyl bromide emission from motor
car exhausts

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1. Transport and distribution between media
4.1.1. Transport in air
4.1.2. Transport in water
4.1.3. Transport in soil
4.1.4. Vegetation and wildlife
4.1.5. Entry into the food chain
4.2. Biotransformation
4.2.1. Biodegradation
4.2.1.1 Soil
4.2.1.2 Stored product fumigation
4.2.2. Abiotic degradation
4.2.2.1 Hydrolysis
4.2.2.2 Light-assisted hydrolysis in water
4.2.2.3 Reaction with the hydroxyl radical
4.2.2.4 Photolysis in the atmosphere
4.2.3. Bioaccumulation
4.3. Interaction with other physical, chemical,
or biological factors
4.4. Ultimate fate following use
4.4.1. Methyl bromide and the ozone layer
4.4.2. Containment, recovery, recycling and disposal
options for methyl bromide

5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

5.1. Environmental levels
5.1.1. Air
5.1.1.1 Global abundance
5.1.1.2 Measured oceanic and coastal air
levels of methyl bromide
5.1.1.3 Measured continental and urban
levels of methyl bromide
5.1.1.4 Vertical profiles of methyl bromide
in the atmosphere

5.1.1.5 Release of methyl bromide to
outside air from greenhouses
5.1.2. Water
5.1.2.1 Seawater
5.1.2.2 Inland waters
5.1.2.3 Waters around greenhouses
5.1.3. Soil
5.1.4. Food
5.1.4.1 After soil fumigation
5.1.4.2 After post-harvest fumigation
5.1.5. Animal feed
5.1.6. Other products
5.1.7. Terrestrial and aquatic organisms
5.2. General population exposure
5.2.1. Food
5.2.2. Drinking-water
5.2.3. Human breast milk
5.2.4. Sub-populations at special risk
5.3. Occupational exposure during manufacture,
formulation, or use
5.3.1. During manufacture
5.3.2. During fumigation
5.3.2.1 Structural fumigation
5.3.2.2 Soil fumigation

6. KINETICS AND METABOLISM

6.1. Absorption
6.1.1. Inhalation
6.1.1.1 Animal studies
6.1.1.2 Human studies
6.1.2. Dermal
6.1.3. Oral
6.1.4. Intraperitoneal injection
6.2. Distribution of methyl bromide and bromide
in tissues
6.2.1. Animal studies
6.2.2. Human studies
6.3. Metabolic transformation
6.3.1. Binding to proteins and lipids
6.3.2. Binding to DNA
6.3.3. The role of glutathione in methyl
bromide metabolism
6.3.3.1 Mammals
6.3.3.2 Insects
6.4. Elimination and excretion in expired air,
faeces, urine
6.5. Retention and turnover
6.6. Reaction with body components

7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

7.1. Soil microorganisms
7.2. Aquatic organisms
7.2.1. Effect of methyl bromide
7.2.2. Effect of bromide ion on aquatic organisms
7.3. Terrestrial organisms
7.3.1. Protozoa
7.3.2. Plants
7.3.2.1 Seed fumigation
7.3.2.2 Fumigation of plants or plant
products
7.3.2.3 The effects on plants of soil
fumigation
7.3.3. Soil invertebrates
7.3.4. Insects and arachnids
7.3.5. Gastropods
7.3.6. Birds
7.3.7. Other animals
7.4. Population and ecosystem effects

8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS

8.1. Single exposure
8.1.1. Oral
8.1.2. Inhalation
8.1.2.1 Guinea-pig and rabbit
8.1.2.2 Mouse
8.1.2.3 Rat
8.1.3. Dermal
8.1.4. Subcutaneous administration
8.2. Short-term exposure
8.2.1. Oral
8.2.2. Inhalation studies
8.2.2.1 Guinea-pig, rabbit, monkey
8.2.2.2 Mouse
8.2.2.3 Rat
8.2.3. Dermal
8.3. Skin and eye irritation
8.4. Long-term exposure
8.4.1. Oral
8.4.1.1 Rat
8.4.2. Inhalation studies
8.4.2.1 Mouse
8.4.2.2 Rat
8.5. Reproduction, embryotoxicity, and teratogenicity
8.5.1. Reproduction and embryotoxicity
8.5.2. Teratogenicity

8.6. Mutagenicity and related end-points
8.6.1. DNA damage
8.6.2. Mutation
8.6.3. Chromosomal effects
8.6.3.1 In vitro studies
8.6.3.2 In vivo studies
8.6.4. Cell transformation
8.7. Carcinogenicity and related end-points
8.7.1. Gavage studies
8.7.2. Inhalation studies
8.8. Special studies
8.8.1. Target organ effects
8.8.1.1 Inhalation studies
8.8.2. Neurotoxicity
8.8.3. Immunotoxicity
8.9. Factors modifying toxicity; toxicity of metabolites
8.10. Mechanisms of toxicity - mode of action

9. EFFECTS ON HUMANS

9.1. Clinical findings
9.1.1. Bromide levels in body tissues and fluids
9.1.2. Dermal exposure
9.1.3. Inhalation
9.2. General population exposure
9.2.1. Poisoning incidents
9.2.1.1 Poisoning associated with fire
extinguishers
9.2.1.2 Poisoning associated with bulk
or house fumigation
9.2.1.3 Poisoning associated with soil
fumigation
9.2.1.4 Miscellaneous incidents
9.3. Controlled human studies
9.4. Occupational exposure
9.4.1. Occupational exposure during manufacture
9.4.2. Occupational exposure due to methyl
bromide fumigation
9.4.2.1 Incidents involving bulk fumigation
9.4.2.2 Incidents involving soil fumigation
9.4.3. Studies measuring the levels of bromide
ion in biological fluids and tissues
9.4.3.1 Manufacturing
9.4.3.2 Fumigation
9.4.4. Haemoglobin adducts as a biological
index to methyl bromide exposure
9.4.5. Neurobehavioural and other studies

10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT

10.1. Human exposure
10.1.1. Relevant animals studies
10.2. Environment

11. RECOMMENDATIONS FOR THE PROTECTION OF HUMAN HEALTH AND THE
ENVIRONMENT

11.1. Human health protection
11.2. Environmental protection
11.3. Recommendations for further research

12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

12.1. FAO/WHO
12.1. IARC
12.3. UNEP

REFERENCES

RESUME

RESUMEN

WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR METHYL BROMIDE

Members

Dr I. Chahoud, Institute for Toxicology and Embryo-pharmacology,
Berlin, Germany

Mr B. Chakrabarti, Ministry of Agriculture, Fisheries and
Food, Slough, Berkshire, United Kingdom

Dr P.E.T. Douben, Her Majesty's Inspectorate of Pollution,
London, United Kingdom (Chairman)

Dr S. Eustis, National Institute of Environmental Health and Safety,
Research Triangle Park, USA (Joint Rapporteur)

Dr K. Fujimori, National Institute of Health Sciences,
Tokyo, Japan

Dr L. Hansen, United States Environmental Protection
Agency, Washington DC, USA

Dr R.F. Hertel, Federal Health Office, Berlin, Germany

Dr J. Kielhorn, Fraunhofer Institute of Toxicology and
Aerosol Research, Hanover, Germany (Joint Rapporteur)

Dr G. Rosner, Fraunhofer Institute of Toxicology and
Aerosol Research, Hanover, Germany

Dr S.A. Soliman, College of Agriculture and Veterinary
Medicine, King Saud University-Al-Qasseem, Bureidah,
Saudi Arabia (Vice-Chairman)

Dr M. Tasheva, National Center of Hygiene, Ecology and
Nutrition, Ministry of Health, Sofia, Bulgaria

Dr P.W. Wester, National Institute of Public Health and
Environmental Protection, Bilthoven, The Netherlands

Prof. C. Zetzsch, Fraunhofer Institute of Toxicology and
Aerosol Research, Hanover, Germany

Observers

Dr W.K. Hayes, Ethyl Corporation, Baton Rouge, LA, USA

Dr M. Spiegelstein, Bromine Compounds Ltd., Beer Sheva,
Israel

Dr P. Montuschi, Catholic University of the Sacred Heart,
Rome, Italy (Representing the International Union of
Toxicology)

Secretariat

Dr D. McGregor, International Agency for Research on
Cancer, Lyon, France

Dr E. M. Smith, International Programme on Chemical
Safety, World Health Organization, Geneva, Switzerland.

NOTE TO READERS OF THE CRITERIA MONOGRAPHS

Every effort has been made to present information in the criteria
monographs as accurately as possible without unduly delaying their
publication. In the interest of all users of the environmental health
criteria monographs, readers are kindly requested to communicate any
errors that may have occurred to the Director of the International
Programme on Chemical Safety, World Health Organization, Geneva,
Switzerland, in order that they may be included in corrigenda, which
will appear in subsequent volumes.

* * *

A detailed data profile and a legal file can be obtained from the
International Register of Potentially Toxic Chemicals, Case
postale 356, 1219 Châtelaine, Geneva, Switzerland (Telephone No.
9799111).

* * *

This publication was made possible by grant number 5 U01
ESO2617-15 from the National Institute of Environmental Health
Sciences, National Institutes of Health, USA, and by financial support
from the European Commission.

ENVIRONMENTAL HEALTH CRITERIA FOR METHYL BROMIDE

A WHO Task Group on Environmental Health Criteria for Methyl
Bromide met at the Fraunhofer Institute for Toxicology and Aerosol
Research, Hanover, Germany, from 9 to 13 August 1993. Dr E.M. Smith,
IPCS, welcomed the participants on behalf of Dr M. Mercier, Director
of the IPCS, and the three IPCS cooperating organizations
(UNEP/ILO/WHO). The Group reviewed and revised the draft and made an
evaluation of the risks for human health and the environment from
exposure to methyl bromide.

The first draft of the EHC on methyl bromide was prepared by Dr
R. F. Hertel and Dr J. Kielhorn at the Fraunhofer Institute of
Toxicology and Aerosol Research in Hanover, Germany. Dr J. Kielhorn
assisted the IPCS Central Unit in the preparation of the second draft,
incorporating comments received following circulation of the first
draft to the IPCS contact points for Environmental Health Criteria
monographs.

Dr E.M. Smith of the IPCS Central Unit was responsible for the
scientific content of the monograph and Mrs M.O. Head, Oxford,
England, for the editing.

The efforts of all who helped in the preparation and finalization
of the monograph are gratefully acknowledged.

1. SUMMARY

1.1 Physical and chemical properties, and analytical methods

Methyl bromide is a colourless gas at room temperature and
standard pressure with a boiling point of about 4 °C. It is heavier
than air and easily liquefied below its critical points. It is
odourless, except at high concentrations, when it has a
chloroform-like smell. It is non-flammable in air, except in the
concentration range of 10-16%, but burns in oxygen. Methyl bromide is
slightly soluble in water but freely soluble in other common solvents.
It can penetrate through many substances, such as concrete, leather,
rubber, and certain plastics.

Methyl bromide hydrolyses to methanol and hydrobromic acid in
aqueous solution, the rate of hydrolysis depending on pH. It is an
effective methylating agent that reacts with amines and
sulfur-containing compounds. Most metals are inert to pure, dry methyl
bromide, but surface reactions take place on zinc, tin, aluminium, and
magnesium in the presence of impurities or moisture. Explosive
reactions with aluminium and with dimethyl sulfoxide have been
reported.

Methyl bromide is commercially available as a liquefied gas.
Formulations for soil fumigation contain chloropicrin (2%) or amyl
acetate (0.3%) as warning agents. Other formulations include up to 70%
chloropicrin or other fumigants or hydrocarbons as inert diluents. For
commodity fumigation, 100% methyl bromide is used.

Analytical methods are described for the determination of methyl
bromide in air, water, soil, food, and animal feed. Direct methods for
determining methyl bromide in air, under field conditions, include
thermal conductivity gas analysers, colorimetric detector tubes,
infra-red analysers, and photo-ionization detectors. Gas
chromatography (GC) with electron capture detection (ECD) is
recommended for routine measurements with occasional mass
spectrometric (MS) confirmation in the laboratory.

Purge and trap techniques as well as headspace sampling are used
for the GC determination of methyl bromide in water. Extraction using
acetone/water followed by headspace capillary gas chromatography with
ECD is recommended for the routine determination of methyl bromide in
foods. As some of the methyl bromide is converted to bromide in soil,
foods, and biological materials, methods of bromide determination are
also discussed. Colorimetric methods, X-ray spectroscopy,
potentiometry, neutron activation analysis, gas chromatography, and
high-performance liquid chromatography (HPLC) are some of the methods
used for bromide determination in various matrices.

1.2 Sources of human and environmental exposure

Oceans are believed to be the major source of methyl bromide. The
main anthropogenic source of methyl bromide is the fumigation of soils
and indoor spaces. A small amount of methyl bromide is emitted from
motor vehicles using leaded petrol.

The world consumption of methyl bromide was over 67 million kg in
1990, an increase of 46% over 1984. It is commonly produced by the
interaction of methanol and hydrobromic acid, and, in some processes,
it is a coproduct together with tetrabromobisphenol A. Methyl bromide
is usually stored and transported as a liquefied gas, under pressure,
in steel containers.

About 77% of the methyl bromide produced is used for soil
fumigation, 12% for quarantine and commodity fumigation, 5% for
structural fumigation, and 6% for chemical intermediates.

The gas is used as a soil fumigant in either fields or
greenhouses for the control of pests. Methyl bromide is applied as a
liquid prior to planting, either by injection into the soil, or by
using evaporating jars under sheeting and allowing it to vaporize in
situ (cold method) or by heating (hot method). The methods permitted
in various countries differ. The type of plastic sheeting is also
important.

Doses of methyl bromide to be applied depend on the legal
standards of different countries, the plant parasite to be controlled
(type, extent of infestation), the following crop, type of soil, and
the plastic cover used (covering time and plastic type). Methyl
bromide is usually applied to soil at dosages of between 50 and 100
g/m^2.

In space fumigation, methyl bromide is used for agricultural
commodity fumigation (e.g., foods, grains, nuts, etc.), termite
control, and rodent control. Dosages of 16-30 g methyl bromide/m³
are used for most goods stored in sealed rooms and silos and under
gas-proof sheets. A period of aeration must follow fumigation.
Fumigation is also important for fresh vegetables and fruits where
quarantine regulations have to be adhered to.

The industrial uses of methyl bromide include organic synthesis,
usually as a methylating agent, and as a low-boiling solvent, e.g.,
for extracting oils from nuts, seeds, and flowers. The uses of methyl
bromide as a refrigerant and as a general fire extinguishing agent are
now only of historical importance.

1.3 Environmental transport, distribution, and transformation

Methyl bromide is present naturally in the atmosphere.
Anthropogenic sources add to this. Although a small amount of methyl

bromide reacts with the hydroxyl radical in the troposphere, some
methyl bromide is transferred to the stratosphere by upward diffusion.
Here photolysis of methyl bromide becomes of increasing importance, it
being the most dominant loss mechanism in the lower stratosphere.
Active bromine species react with ozone in the stratosphere and are
thought to be partly responsible for the destruction of the ozone
layer.

In soil, methyl bromide is partially hydrolysed to bromide ion.
After fumigation using methyl bromide, soil can be leached with water
to prevent the bromide ions formed being taken up by plants
subsequently planted on the sterilized soil. This increase in bromide
levels may cause problems when surface water is used for leaching.
Methyl bromide may diffuse through polyethylene drinking-water pipes,
if the surrounding soil has been fumigated with methyl bromide.

In the soil, methyl bromide can diffuse to a depth of 0.8 m,
depending on the soil type, dosage, method of application, and length
of fumigation, the highest content of methyl bromide remaining in the
upper soil. The transport of the gas is caused by mass flow and
molecular diffusion, but it is also influenced by simultaneously
occurring sink processes, such as sorption and dissolution, and
irreversible sink processes, such as hydrolysis. The amount of methyl
bromide converted to bromide depends mainly on the organic matter
content of the soil. The bromide produced is largely water soluble and
can be taken up by plants or removed to lower soil levels by leaching
with water.

In plants, the amount of bromide accumulated depends on various
factors, such as dosage, exposure time, aeration rate, the physical
and chemical properties of the soil, the climatic trend (temperature
and rainfall), the plant species, and the type of plant tissue.
Especially leafy vegetables, such as lettuce and spinach, can take up
relatively large amounts of bromide ion without phytotoxic symptoms.
In contrast, other crops, such as carnations, citrus seedlings,
cotton, celery, peppers, and onions, are particularly sensitive to
methyl bromide fumigation.

Methyl bromide and its reaction products, of which only bromide
has been considered up to now, can enter the food chain in two ways;
through consumption of food grown in greenhouses or fields fumigated
before planting, or through eating food fumigated with methyl bromide
during storage. At certain levels, bromide may be hazardous for health
and tolerance levels are given for bromide in foodstuffs. Levels of
other reaction products have not been investigated.

Methyl bromide is degraded in soil by hydrolysis and microbial
degradation. The rate constant for hydrolysis varies with temperature
and pH and is enhanced by light.

The octanol/water partition coefficient (log P_ow) of methyl
bromide is 1.19, suggesting a low bioaccumulation.

The methyl bromide that is not degraded during fumigation finds
its way into the troposphere and by upward diffusion into the
stratosphere. There does not seem to be a significant vertical
gradient for methyl bromide in the troposphere, but levels decrease
rapidly in the lower stratosphere where photolysis takes place.

1.4 Environmental levels and human exposure

Methyl bromide concentrations, measured in the air in unpopulated
areas, range from 40 to 100 ng/m³ (10 to 26pptv), readings in the
Northern hemisphere being higher than those in the Southern
hemisphere. Most readings are in the range of 9-15 pptv. Seasonal
differences have been found in some studies. In urban and industrial
areas, the levels are much higher, with average values of up to 800
ng/m³ and with some readings as high as 4 µg methyl bromide/m³. In
the proximity of fields and greenhouses, during fumigation and
aeration, the concentrations of methyl bromide are considerably
higher, values of 1-4 mg/m³ being measured in one study at distances
of up to 20 m from a greenhouse, a few hours after injection; a tenth
of this value was found 4 days later.

The methyl bromide concentration in a sample of surface seawater
has been given as 140 ng/litre. The average value of bromide ion
concentrations in samples of coastal water near the North Sea was 18.4
mg/litre; the level of bromide ion in inland rivers was much lower,
except in regions where fumigation with methyl bromide was practised,
or, in areas of industrial pollution. In drainage water from a
Netherlands greenhouse, levels of 9.3 mg methyl bromide/litre and 72
mg bromide ion/litre were reported. In water discharged from a Belgian
greenhouse, a value of 280 mg bromide/litre was recorded after
fumigation.

The natural bromide content of soil depends on the soil type, but
is usually less than 10 mg/kg. The residue of bromide in fumigated
soil depends on treatment, dosage, type of soil, amount of rain or
leaching water, and temperature.

Levels of methyl bromide or bromide may be elevated in foods that
have either grown on soil previously treated with methyl bromide or
have been fumigated post-harvest.

On rare occasions, bromide levels in fresh vegetables, grown on
soils previously fumigated with methyl bromide, have been observed to
exceed the permitted residue level. In some countries, it is not
permitted to grow vegetables on treated soils.

Methyl bromide is widely used for fumigating post-harvest
commodities, such as wheat and cereals, spices, nuts, dried and fresh
fruits, and tobacco. Methyl bromide concentrations usually decrease
rapidly after aeration and residues are not detectable after some
weeks. Some foods, such as nuts, seeds, and fatty foods like cheese,
tend to retain methyl bromide and inorganic bromide.

Individuals may be exposed to the fumigant and residues of
bromide ion. There could also be a risk of methyl bromide or increased
bromide contents in water in shallow wells near methyl bromide
fumigation operations.

People living in close proximity to fields, greenhouses, or
stores fumigated with methyl bromide, could be at risk of exposure to
the gas. Individuals can also be endangered if they accidentally, or
deliberately, enter private houses that have been fumigated to
eradicate pests before it is declared safe to do so.

Occupational exposure to methyl bromide is the most probable
hazard for operators during production, filling processes, and
fumigation operations. Because of strictly applied safety measures in
production facilities, only fumigators are now considered a high-risk
group. Fumigators engaged in structural fumigation may encounter
exposure much higher than the TLV after 24 h aeration (80-2000
mg/m³). However, properly trained operators will use appropriate
protective equipment. Field workers during soil fumigation may be
exposed for longer periods of time to transient doses of methyl
bromide. Because of the nature of greenhouse fumigation, operators may
also encounter higher concentrations (100-1200 mg/m³). However, risk
management developed for various aspects of fumigation requires strict
safety procedures and the use of protective equipment. Despite this,
individual cases of accidental overexposure still occur.

1.5 Kinetics and metabolism

Inhalation studies on rats, beagles, and humans have shown that
methyl bromide is rapidly absorbed through the lungs. It is also
rapidly absorbed in rats following oral administration.

After absorption, methyl bromide or metabolites are rapidly
distributed to many tissues including the lung, adrenal gland, kidney,
liver, nasal turbinates, brain, testis, and adipose tissue. In an
inhalation study on rats, the methyl bromide concentration in tissues
reached a maximum 1 h after exposure, but decreased rapidly, with no
traces 48 h later. The metabolism of inhaled methyl bromide has not
yet been elucidated, though glutathione may play a role.

Methylation of proteins and lipids has been observed in the
tissues of several species, including humans, exposed via inhalation.
Methylated DNA adducts have also been detected following the in vivo
and in vitro exposure of rodents or rodent cells.

In inhalation studies using [¹⁴C] labelled methyl bromide, the
exhalation of ¹⁴CO₂ was the major route of elimination of ¹⁴C.
A lesser amount of ¹⁴C was excreted in the urine. Following oral
administration of methyl bromide, urinary excretion was the major
route of elimination of ¹⁴C.

The central nervous system is an important target for methyl
bromide. Changes in monoamine, amino acid contents and, possibly,
catecholamine contents may be factors involved in methyl
bromide-induced neurotoxicity.

1.6 Effects on organisms in the environment

Methyl bromide is used commercially to control nematodes, weeds,
and soil-borne fungi that cause diseases, such as damping off, crown
rot, root rot, and wilt.

There are few studies on the effects of methyl bromide on aquatic
organisms, as methyl bromide itself is only slightly soluble in water.
Values for LC₅₀ range from a 4-h value of 17 mg/litre for Cyprinus
carpio L. to a 48-h value of 1.2 mg/litre for Poecilia reticulata.
At lethal concentrations, damage to the gills and oral epithelia was
the probable cause of death.

Bromide ion is formed from methyl bromide after fumigation and is
found in water after leaching. Bromide ions showed acute toxicity in
various freshwater organisms at concentrations ranging from 44 to 5800
mg Br^-/litre; the no-observed-effect concentration (NOEC) in
long-term tests varied from 7.8 to 250 mg Br^-/litre. Bromide ions
markedly impaired reproduction in both crustaceans and fish.

As a fumigant, methyl bromide can be applied directly to plant
seeds, plant cuttings, or harvested plant products, for disinfestation
during transportation and storage. Delay in germination or loss of
germinative capacity can occur if the moisture level or temperature is
too high.

Some crops, particularly leafy vegetables, are sensitive to
methyl bromide fumigation because of excess bromide in the soil, or,
indirectly because of effects on soil microflora. Sometimes, methyl
bromide has a positive effect on plants, increasing growth and crop
yields.

Methyl bromide fumigation eradicates not only target organisms
but also part of the soil flora, gastropods, arachnids, and
protozoans.

Methyl bromide is often used in preference to other insecticides
because of its ability to penetrate quickly and deeply into bulk
materials and soils. Dosages for methyl bromide as a storage fumigant
range mainly from 16 to 100 g/m³ for 2-3 days, the dosage depending

on temperature. A higher dosage is required to kill eggs and pupae
than adult insects. There is a variation in tolerance between
different insect species and stages and between different strains of
the same insect.

There are no data on the direct effects of methyl bromide on
birds and wild mammals.

1.7 Effects on experimental animals

Inhalation studies conducted on various mammalian species have
shown that there are clear species-related and sex-related differences
in susceptibility to methyl bromide. There was a steep dose-mortality
response in all animal species tested.

Neurological manifestations were the major clinical signs of
toxicity in rats and mice and, at higher concentrations, irritation of
the mucosal membranes was also observed.

Neurological manifestations included twitching and paralysis. At
lower dosages, changes in locomotor activity, dysfunction of the
peripheral nerve changes in circadian rhythm, and conditioned taste
aversion, have been reported by various authors.

Histopathological changes have been described in the brain,
kidney, nasal mucosa, heart, adrenal gland, liver, and testis of rats
and mice exposed to various levels of methyl bromide.

Olfactory sustentacular and mature sensory cells are damaged by
short-term exposure to methyl bromide, but there is rapid repair and
recovery.

Long-term inhalation studies (up to 2 years) on rats showed
lesions in the nasal mucosa and myocardium. In a similar long-term
study on mice, the primary toxic effects were observed in the brain,
heart, and nasal mucosa. Evidence of carcinogenicity was not observed
in either species.

Oral administration of 50 mg methyl bromide/kg body weight to
rats for up to 25 weeks produced inflammation and severe hyperplasia
of the forestomach epithelium. Following a post-exposure recovery
period, fibrosis of the forestomach was the principle lesion observed.
An early carcinoma of the forestomach was observed in the rat treated
daily for 25 weeks.

B6C3F mice and F344 rats exposed to up to 467 mg methyl
bromide/m³ for 13 weeks showed slight changes in sperm morphology
while the length of the estrous cycle was not affected.

Inhalation exposure to up to 350 mg methyl bromide/m³ did not
induce any noteworthy effects on the growth, reproductive processes,
and offspring of two consecutive generations of CD Sprague-Dawley
rats. The male and female fertility indices were reduced at the two
highest dose levels in the F₁ generation F_2B litter.

In studies on developmental toxicology with New Zealand White
rabbits, exposure to 311 mg methyl bromide/m³ (6 h/day; days 7-19 of
gestation) showed moderate to severe maternal toxicity. Developmental
effects, observed at the maternal toxic dose, consisted of decreased
fetal weights, an increase in the incidence of a minor skeletal
variation, and malformations (mostly missing gallbladder or missing
caudal lobe of the lung). However, at 272 mg/m³, maternal toxicity
was less marked and there were no embryotoxic effects.

No adverse maternal, embryonal, or fetal effects were observed in
rabbits exposed to 78 or 156 mg methyl bromide/m³. A
no-observed-effect level (NOEL) of 156 mg methyl bromide/m³ was
given for maternal and development toxicity in New Zealand White
rabbits.

Methyl bromide has been found to be mutagenic in several in
vitro and in vivo test systems. It induces sex-linked recessive
lethal mutations in Drosophila melanogaster and mutations in
cultured mammalian cells. It does not induce unscheduled DNA synthesis
or cell transformation in cultured mammalian cells. DNA methylation of
the liver and spleen was observed in mice administered methyl bromide
by various routes. Micronuclei were induced in bone-marrow and
peripheral blood cells of rats and mice.

The mechanism of methyl bromide toxicity is not known.

1.8 Effects on humans

Human exposure to methyl bromide may occur through inhalation of
the gas or contact with the liquid. Exposure through ingestion of
drinking-water contaminated with leaching water can also occur.

A controlled human study showed that uptake following inhalation
exposure was about 50% of the administered dose.

Methyl bromide is damaging to the nervous system, lung, nasal
mucosa, kidney, eye, and skin. Effects on the central nervous system
include blurred vision, mental confusion, numbness, tremor, and speech
defects. Topical exposure can cause skin irritation and burns, and eye
injury.

Exposure to high levels of methyl bromide causes pulmonary
oedema. Central nervous system depression with respiratory paralysis
and/or circulatory failure are often the immediate cause of death,
which is preceded by convulsions and coma.

Several different neuropsychiatric signs and symptoms have been
observed during acute and long-term methyl bromide poisonings.
Low-level short-term exposures to the vapour have produced a syndrome
of polyneuropathy without overt central manifestations.

Late sequelae include bronchopneumonia after severe pulmonary
lesions, and renal failure with anuria and severe weakness with, or
without, evidence of paralysis. Generally, these symptoms tend to
subside over a period of a few weeks or months. However, deficits
without recovery usually characterized by sensory disturbances,
weakness, disturbances of gait and blurred vision, have been observed.

Exposure to methyl bromide is accompanied by an increase in the
bromide level in the blood. In fumigators, there is a relationship
between the number of gas applications and the average plasma bromide
level.

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL METHODS

2.1 Identity

2.1.1 Primary constituent

Chemical formula: CH₃Br

Chemical structure:

H
'
H - C - Br
'
H

Relative molecular mass: 94.94

Common name: methyl bromide; bromomethane

CAS name: bromomethane

CAS registry number: 74-83-9

EEC No. 602-002-00-2

EINECS No. 200-813-2

Synonym: monobromomethane

2.1.2 Technical product

Methyl bromide is typically available as a liquefied gas
(Matheson Gas Data Book, 1980).

Purity: > 99.5%

Max. water content: 0.015%

Max. acidity (as HBr): 0.0010%
(Matheson Gas Data Book, 1980)

Impurities: traces of chloromethane
(Atochem, 1988)

Formulations include mixtures with other fumigants, most
frequently with chloropicrin or hydrocarbons, as inert diluents
(Stenger, 1978). Chloropicrin (2%) or amyl acetate (0.3%) are added to
methyl bromide to serve as a warning agent. Chloropicrin is a toxic
chemical with lacrimatory and irritating effects. However, it is

sensed at the 9 mg/m³ (1.3 ppm) level and a methyl bromide
concentration could be well above regulatory exposure limits by the
time the presence of chloropicrin is noticed.

Chemical, environmental, and toxicological data concerning
chloropicrin have been reviewed by Sassaman et al. (1986). For
commodity fumigation, 100 % methyl bromide should be used (Ethyl
Corporation, 1990).

Methyl bromide is marketed under several different trade names,
with formulations containing 30-100 % of the compound, e.g.,
Brom-o-gas, Desbrom, Haltox, MBR-2, Metabrom, Methybrom, Methyl
Bromide, Methyl-o-gas, Sobrom 9B, Terr-o-gas 100 (all 98-100% methyl
bromide); Bromopic, Sobrom 67, Terr-o-gas (80-30%, with decreasing
methyl bromide and increasing chloropicrin content).

2.2 Physical and chemical properties

2.2.1 Physical properties

Methyl bromide is a colourless gas at normal temperature and
pressure. Under increased pressure or below about 3 °C it is a clear,
colourless to straw-coloured liquid. It is odourless except in
relatively high concentrations, when it has a chloroform-like smell
(Matheson Gas Data Book, 1980). Individual odour thresholds range
between 80 mg/m³ and 4000 mg/m³ (Ruth, 1986).

The gas can penetrate many substances, including concrete,
leather, and rubber (Bond, 1984) as well as brick and wooden walls
(BBA, 1989). Methyl bromide did not permeate through certain plastics
(Herzel & Schmidt, 1984) or through metal or polyvinyl-chloride (PVC)
pipes, but permeation through low-density polyethylene (LDPE)
occurred. Permeation through LDPE pipes resulted in a concentration of
6% in the contained water after one week. This was independent of the
actual concentration outside the pipes. The methyl bromide seemed to
concentrate within the polymer. Permeation through high density
polyethylene (HDPE) was 5-8 times lower than through LDPE (Veenendahl
& Dibbets, 1981).

Liquid methyl bromide has a solvent action on many plastics and
organic materials. Natural rubber is attacked and acquires a strong
unpleasant smell (Thompson, 1966).

The physical properties of methyl bromide are summarized in Table
1.

Table 1. Physical properties of methyl bromide

Freezing point (1 atm): -93 °C^a,b

Boiling point (1 atm): 3.56 °C^a,b

Flash point: 194 °C, burns with difficulty^c

Flammability: 13.5-14.5 % (by volume; flammable limits in air)^a
10-16%^d

Critical temperature 194 °C^c

Autoignition temperature: 536.7 °C^a

Vapour pressure (20 °C): 1893 kPa (1420 mmHg)^b,e

Density (20 °C): 3.974^b
(kg/m³) (0 °C): 1730^a,b,c

Vapour density: 3.27^c
(rel.; air=1) (20 °C)

Solubility in water: 18.5^f (15.4 at 25 °C)^f
(g/litre; 20 °C) 18.00^g
16^h
forms a voluminous crystalline hydrate
(CH₃Br.2OH₂O) below 4 °C^b

Solubility in other freely soluble in alcohol, chloroform, ether,
solvents: carbondisulfide, carbontetrachloride, and benzene^b

log ^n-octanol/water partition 1.19^i,j
coefficient (log P_ow):

Table 1. Con't

Henry's law constant: 0.533 (calculated using atmospheric
(kPa m³/mol) pressure)^b

UV absorption: max. 202 nm^k,l,m

^a = Matheson Gas Data Book (1980); ^b = Windholz (1983);
^c = Hommel (1984); ^d = NFPA (1984); ^e = Stenger (1978);
^f = Wilhelm et al. (1977), ^g = Mackay & Shiu (1981); ^h = Atochem (1987);
ⁱ = Hansch & Leo (1979); ^j = Sangster (1989); ^k = Robbins (1976b);
^l = Molina et al.(1982); ^m = Gillotay et al. (1989).

There are discrepancies in values for the solubility of methyl
bromide in water, some values in the literature being substantially
lower than those given in Table 1.

Methyl bromide is practically non-flammable in air, a narrow
range of 13.5-14.5 % by volume being quoted in the Matheson Gas Data
Book (1980), whereas a range of 16-20% is given in NFPA (1984). It
burns in oxygen (Windholz, 1983).

2.2.2 Chemical properties

Methyl bromide hydrolyses to methanol and hydrobromic acid. It is
a methylating agent reacting with amines, particularly the more basic
ones, to form methylammonium bromide derivatives. Methyl bromide also
reacts with sulfur compounds under alkaline conditions to give
mercaptans, thioethers, and disulfides. Most metals, other than
aluminium, are inert to pure, dry methyl bromide, but surface
reactions take place on zinc, tin, and magnesium, in the presence of
ethanol or moisture (Stenger, 1978). Explosions upon contact with
aluminium, as well as with dimethyl sulfoxide, have been reported
(NFPA, 1984). The liquid is corrosive to aluminium, magnesium and zinc
metals and their alloys.

Methyl bromide is not considered to be flammable. However, it
will burn in air in the presence of a high-energy source of ignition
and when within a narrow flammability range (see section 2.2.1).
Methyl bromide has no flash point. Thermal decomposition in a glass
vessel begins above 400 °C (Stenger, 1978). The products include HBr,
bromine, carbon oxybromide, as well as carbon dioxide and carbon
monoxide (von Oettingen, 1964).

2.3 Conversion factors

1 ppm = 3.89 mg/m³ at 25 °C, 1013 hPa
or 3.95 mg/m³ at 20 °C, 1013 hPa

1 mg/m³ = 0.257 ppm

1% methyl bromide = 10 000 ppm = 39.52 g/m³
at 20 °C and 101.3 kPa

2.4 Analytical methods

Methyl bromide residues have been determined indirectly as total
inorganic bromide. Methods are now available for the direct
determination of methyl bromide.

2.4.1 Methyl bromide in air

A summary of methods for the detection of methyl bromide in air
is given in Table 2.

The detection of methyl bromide in air is important at three
levels: control readings for warning fumigation workers; working place
(e.g. production/packing and sealing/transport) measurements; and the
measuring of levels of methyl bromide in the atmosphere.

In the first case, exposed fumigation workers must be warned
immediately of the presence of methyl bromide, as it is a toxic gas.
Many formulations, particularly those for commodity fumigation, do not
contain chloropicrin as a sensory warning.

Halide lamps cannot detect methyl bromide around occupational
exposure thresholds of 20 mg/m³ whereas electronic gas detectors,
though not specific for methyl bromide, are extremely sensitive.
Currently available gas detector tubes are also not specific for
methyl bromide but can be used to provide a reasonably precise
indication of methyl bromide level in a fumigation area before entry.

Direct reading colorimetric indicators are available (Saltzman,
1983; Leichnitz, 1985). However, Guillemin et al. (1990) noted that
several batches of these tubes produced unreliable results.

There is a direct-reading infrared analyser (MIRAN) that monitors
from 10 mg/m³ (2.3 ppm) methyl bromide (Foxboro, 1989). As this
instrument can measure methyl bromide below the threshold value, it
has been used to determine whether buildings are safe for occupation
after fumigation. However, Guillemin et al. (1990) reported that the
portable systems were mechanically and electrically unstable under
field conditions, and showed poor sensitivity and selectivity for
methyl bromide.

Table 2. Methods for the analysis of methyl bromide in air^a

Sampling Analytical Detector Detection Comment Reference
method method limit

Gas collected by pump GC (30 m ECD used for ambient Harsch & Rasmussen
and pressurized capillary column) air (1977)
a ) isothermal runs 40 ng/m³ determinations
b ) temperature 2 ng/m³
programmed freeze-
out technique

Injection of 5 ml sample GC ECD 2 µg/m³ no common pollutants Pellizzari et al.
(3 m steel (scandium (upper interfere (1978)
column) tritide) limit with estimation
1 mg/m³⁾

Adsorb on charcoal; 100 m glass MS 14 ng/m³ Pellizari et al.
desorb (heat, purge with capillary column (21°C) (1978)
helium); dry (calcium
sulfate); readsorb
(Tenax GC); desorb as
before; trap liquid
nitrogen cooled;
vaporize onto GC

Adsorb (polymeric ECD 500 ng/m³ Krost et al. (1982)
beads); desorb (heat,
purge with helium);
trap directly on GC
column

Gas collected by pump GC ECD 40 µg/m³ Angerer (1982)
(2 m steel column)

Table 2 (continued)

Sampling Analytical Detector Detection Comment Reference
method method limit

Adsorb on charcoal; GC FID 1 mg/m³ Eller (1985),
desorb (carbon disulfide Peers (1985)
inject aliquot

Not given GC FID 2 ng for fumigation Dumas & Bond (1985)
control

Not given GC PID 10 pg for ambient air Dumas & Bond (1985)
sampling

Direct capillary GC ECD 50 ng/m³ methyl bromide and Kallio & Shibamoto
trapping with pump chloropicrin (1988)
detected

Charcoal air sampling GC ECD 50 ng designed to handle Woodrow et al. (1988)
tube/headspace sampler large numbers of
samples (45 samples
in 24 h); not specific
for methyl bromide

HBr-treated activated GC FID 1 mg/m³- personal monitoring Lefevre et al. (1989)
charcoal tubes/solvent ECD 1 g/m³ method
desorption

^aAbbreviations:
ECD = electron capture detector; HECD = Hall electroconductivity detector;
FID = flame ionization detector; MS = mass spectrometry;
GC = gas chromatography; PID = photoionization detector.

Portable gas chromatographs measuring down to 0.04 mg/m³ (0.01
ppm) are also available for field work (Bond, 1984). Guillemin et al.
(1990) recommended for field conditions a photo-ionization detector
using a 10.2 eV source previously calibrated in the laboratory for
methyl bromide. The limitations were that readings were not specific
for methyl bromide and that sensitivity decreased with time.

Linenberg et al. (1991) used a portable GC with an argon
ionization detector (AID) to identify methyl bromide (0.12 mg/m³; 31
ppb) in the presence of other halohydrocarbon compounds for on-site
analysis.

In situ measurement of methyl bromide in indoor air using long
path Fourier transform infrared (FTIR) spectroscopy has been described
(Green et al., 1991). Quantitative determinations were made by
comparison with reference spectra of known concentration. Detection
limits were given as 0.14 mg/m³ (35 ppb), but conditions could be
optimized to obtain more sensitivity.

Methyl bromide is present in the atmosphere and its degradation
products may react with the ozone layer (see section 5.1.1).

Air samples can be collected using the following methods:

- cryogenesis using liquid nitrogen or helium,

- adsorption on (activated) charcoal,

- pumping into special containers,

- entry into already evacuated containers (BUA, 1987).

Plastic tubing or containers must not be used as they absorb
methyl bromide (Herzel & Schmidt, 1984).

Methods using electron capture detectors (ECD) are suitable for
routine measurements. GC/MS may be used for confirmation purposes.

In the monitoring of methyl bromide in air, stainless steel
canisters are recommended for collection with analysis using automated
cryogenic preconcentration followed by gas chromatography with a
selective detector - flame ionization (FID) and electron capture
detectors (ECD) connected in parallel (Jayanty, 1989).

2.4.2 Methyl bromide in water

Methods of determination of methyl bromide in water are
summarized in Table 3.

Purge and trap techniques, as well as headspace sampling, have
been used for the GC determination of methyl bromide in water. Details
of the collection, preservation, and handling of the water sample to
be analysed for methyl bromide are given in most references mentioned
in this section.

The headspace sampling technique can be used for analysis of
virtually any matrix.

Wylie (1988) compared headspace with purge and trap techniques
for the analysis of volatile priority pollutants. The headspace method
is more easily automated running 24 samples against only up to 10 with
a purge and trap unit with autosample. There is also less chance of
contamination from foaming or from high concentrations of a previous
analyte with headspace. Virtually any matrix can be used with
headspace, and glassware is disposable, which minimizes contamination.
Under some conditions, purge and trap is more sensitive than
headspace. US EPA recommended the purge and trap method for the
analysis of volatiles (EPA; 1984a).

An evaluation of methods for testing groundwater recommended in
US EPA Methods 8010 (GC/ECD) and 8240 (GC/MS) gave practical
quantification limits of 20 and 10 µg/litre, respectively, for methyl
bromide (Garman et al., 1987).

US EPA Methods 601 (GC/ECD), 602 (GC/MS) (Driscoll et al., 1987;
Duffy et al., 1988) and 624 (GC/MS) (Lopez-Avila et al., 1987) have
been updated for use with capillary column GC, to provide greater
sensitivity.

A sensitive headspace method for the gas-chromatographic
determination of methyl bromide in surface and drinking-waters was
reported by Cirilli & Borgioli (1986). This method is based on the
conversion of methyl bromide into methyl iodide by reaction with
sodium iodide.

Table 3. Determination of methyl bromide in water^a

Sampling method Analytical Detector Detection Comment Reference
method limit

Headspace GC ECD 1 µg/litre Wegman et al. (1981)

Purge and trap GC ECD (n.d.)^a US EPA (1982a)
(Method 8010)

Purge and trap GC MS 5 µg/litre US EPA (1982b)
(Method 8240)

Purge and trap GC MS (n.d.)^a US EPA (1984a)
(packed column) (Method 624)

Purge and trap GC ECD 1.18 µg/ US EPA (1984b)
desorb as vapour litre (Method 601)
(heat to 180 °C,
backflush with inert
gas) on to GC column

Add internal standard GC MS 50 µg/litre US EPA (1984c)
(isotope labelled (Method 1624)
methyl bromide); purge,
trap and desorb as above

Purge (80 °C, nitrogen); GC ECD 0.05 µg/ Piet et al. (1985)
trap (Ambersorb or litre
Porapak N); desorb MS 0.05 µg/
(flash-heat) and trap litre
in "mini-trap"
(Ambersorb or Porapak N,
- 30°C); desorb (flash-
heat) on to GC column

Table 3 (continued)

Sampling method Analytical Detector Detection Comment Reference
method limit

Headspace capillary GC ECD 5 x 10-³ methyl bromide Cirilli & Borgioli
µg/litre converted quantitatively (1986)
to methyl iodide, which
is then determined

Purge and trap capillary GC ECD optimization of methods Driscoll et al. (1987)
PID 601, 602 to capillary Duffy et al. (1988)
column

Purge and trap capillary GC MS updating of methods; Lopez-Avila et al.
no separation of (1987)
bromomethane from
chloromethane

Headspace sampling capillary GC MS 20 µg/litre Gryder-Boutet &
Kennish (1988)

Samples purged for capillary GC FID 1 µg/litre Cochran (1988)
45 seconds directly
to a cryogenically
cooled, capillary
column

Purge and trap capillary GC ECD 1.1 µg/litre Ho (1989)

^a For other abbreviations see Table 2.
n.d. = methyl bromide was not detected in the earlier determinations.

Singh et al. (1983) described the analysis of methyl bromide in
seawater samples. A 50-ml volume of seawater and an equal volume of
ultra-pure air were enclosed in all-glass syringes of 100-ml volume.
Once in the syringe, the equilibrium was allowed to reach completion
(enhanced by repeated shaking) in 15-30 min. This also allowed the
water to reach room temperature, which was carefully recorded. The air
in equilibrium with the 50-ml seawater was analysed for methyl bromide
using gas chromatography with ECD; the corresponding equilibrium
concentration of methyl bromide in seawater was determined from
solubility data at the measured room temperature, and the two were
added to obtain the methyl bromide concentrations in seawater. The
partition coefficient data and their temperature dependence for methyl
bromide were taken from Wilhelm et al. (1977) for pure water. The
salting-out coefficient of 1.2 was determined on the basis of
available data on the measured solubility of moderately soluble gases
in pure water and seawater.

2.4.3 Determination of methyl bromide in soil

Equipment and methods for sampling and analysing deep field soil
atmospheres have been described (Kolbezen & Abu-El-Haj, 1972). Soil
atmosphere samples were obtained from a vertical and horizontal grid
of sampling points placed into the soil before it was treated with
methyl bromide. The samples were withdrawn through fine stainless
steel tubing into syringes that could be transported to the laboratory
and directly applied to the gas chromatograph. A flame ionisation
detector (FID) was used (detection limit 40 mg/m³).

US EPA Methods 8010 and 8240 (Table 3) can also been used for the
determination of methyl bromide in solid waste and soils (US EPA,
1982a,b) with a detection limit of 1 µg/g. Extraction of non-aqueous
samples is carried out using methanol or polyethylene glycol.

2.4.4 Methyl bromide in cereal grains and other foods

Analytical methods are summarized in Table 4.

Table 4. Determination of methyl bromide in plant material and foods^a

Medium Sampling method Analytical Detector Detection Comment Reference
method limit

Flour, cold solvent extraction, GC FID 0.3 mg/kg 95% recovery Heuser & Scudamore
unground extraction time (1968; 1970),
wheat, increasing with food Scudamore (1987)
sultanas, particle size
peanuts,
maize,
ground-nuts

Whole wheat, extracted methyl GC ECD 0.01 mg/kg Fairall & Scudamore
flour, ground- bromide is reacted (1980)
nut, rapeseed, to form methyl iodide
dried milk
powder, cocoa
beans

Grain acetone/water GC (Carbo- ECD 0.05 mg/kg Greve & Hogendoorn
extraction; headspace wax-20 M) (1979)
analysis

Wheat flasks containing GC FID 0.3 µg/kg determination of Dumas (1982)
wheat flushed with (2 m Tenax) methyl bromide in
nitrogen and trap at wheat after
-78.5 °C fumigation

Grapefruit blended with water GC ECD 0.1 mg/kg King et al. (1981)
and vial sealed, 5 ml 2 µg/kg
headspace gas removed
with syringe and
injected

Table 4 (continued)

Medium Sampling method Analytical Detector Detection Comment Reference
method limit

Wheat, water added, GC ECD 0.4 µg/kg De Vries et al.
flour, equilibration at 30 °C (1985)
cocoa, headspace
peanuts

Cereal extract with acetone: GC ECD 150 µg/kg Scudamore (1985a)
grains water; add sodium
and chloride; separate
other layers; dry acetone
foods solution over
anhydrous calcium
chloride; inject
aliquot

extract with acetone: GC ECD 10 µg/kg Scudamore (1985b)
water, inject aliquot
of headspace vapour

Cherries headspace; adapted GC ECD 0.5 mg/kg determination of the Sell et al. (1988)
from King et al. rate of desorption
(1981) from fumigated
cherries

Apples headspace; adapted GC ECD 0.01 mg/kg Sell & Moffitt (1990)
from King et al.
(1981)

Table 4 (continued)

Medium Sampling method Analytical Detector Detection Comment Reference
method limit

Food extraction with 83% GC ECD, 55 µg/kg poor recovery and Daft (1987; 1988;
acetone (grains), 20% (packed HECD 20 µg/kg high coefficient 1989)
acetone (softer foods); column) of variation
residues partitioned
into isooctane by
shaking; fatty food
passed through micro-
Florisil columns

Nuts, comminuted food sample GC ECD dependent Page & Avon (1989)
food with sodium sulfate; (capillary) on lipid
aliquot to headspace; content of
cryogenic focusing at food 0.15-
-60°C and then elution by 0.65 µg/kg
temperature programming

Nuts extraction with sodium GC ECD, suitable for Daft (1992)
sulfate at 80 °C; purge (capillary) HECD screening nut
overnight samples at ng/g
levels; 40%
recovery; 29%
coefficient of
variation

Fish homogenization GC MS 200 µg/kg Easley et al. (1981)
purge and trap

^aFor abbreviations see Table 2.

Although bromide levels in food have been measured and documented
for several decades, the methods for the determination of methyl
bromide in foods are still being refined. The cold extraction or
soaking procedure was developed and optimum extraction times
determined for several foods, the extraction time increasing with food
particle size (Heuser & Scudamore, 1968, 1970). With several foods,
there was evidence of methyl bromide loss through reaction with food
components. The following extraction times for methyl bromide were
reported: flour (1 h), unground wheat (8 h), sultanas (8 h), peanuts
(8 h), maize (24 h), groundnuts (24 h), and cocoa beans (48 h). When
the procedure was reevaluated, it was found that the longer extraction
time required for unground grain, compared with flour, probably
reflected the migration of methyl bromide into the interior of the
grain (Scudamore, 1987).

An acetone/water extraction of grain followed by headspace
analysis was described by Greve & Hogendoorn (1979). The headspace
method has also been developed for sampling other selected foods,
e.g., grapefruit (King et al., 1981), flour, cocoa, unground wheat,
and peanuts (DeVries et al., 1985), cherries and apples (Sell et al.,
1988; Sell & Moffitt, 1990).

Headspace capillary gas chromatography with electron capture
detection was described by Page & Avon (1989). The difference between
this and other headspace procedures is the particle size reduction by
the blending or homogenization of the cold or frozen sample with ice
and cold water with only minimal loss of methyl bromide, resulting in
a rapid 1-h equilibrium in the headspace vial. An advantage of
headspace is that nonvolatile material is not introduced into the
chromatographic column or injector body, thus shortening the run. The
method is sensitive with detection limits of 0.15-0.65 µg/kg. These
different detection limits are due to an inverse relationship of
methyl bromide headspace response and food lipid content. Duplicate
samples from the same vial are not possible, and, for quantification,
a separate calibration curve is necessary for each food item.

Combining the methods of Page & Avon (1989) and Daft (1987, 1988,
1989), an improved method for the detection of methyl bromide in nuts
was developed using extraction with sodium sulfate solution at 80 °C
and purging overnight (Daft, 1992). A Hall electrolytic conductivity
detector, used in the determinative step, has been found to be about
3 times more sensitive to methyl bromide than ECD. Additionally, the
Hall detector is said to eliminate endogenous interference from the
nut samples. The recovery was 40% (coefficient of variation, 29%) and
the method can be used to screen assorted nut samples for ng/g levels
of incurred residues.

Siegwart (1987) suggested using the headspace method for
screening, but that with positive findings, the methyl bromide
concentration should be confirmed using mass spectography. In

addition, methyl bromide should then be converted to methyl iodide and
determined again. A detection limit of under 10 µg/kg, is given.

US EPA Method 624 (GC/MS) has been adapted for the determination
of methyl bromide in fish (Easley et al., 1981).

2.4.5 Methyl bromide in serum, plasma and blood, and post-mortem
tissue

Marraccini et al. (1983) used a purge and trap method followed by mass
spectroscopy to determine methyl bromide levels in post-mortem
tissues. Tissue levels lower than 1 mg/kg (1 ppm) were detectable.

Honma et al. (1985) detected methyl bromide in rat tissues using
GC/ECD. The tissues were extracted with toluene. The presence of
methyl bromide was confirmed by GC/MS. No detection limit was given
but the lowest values reported were 1 ng/g.

Headspace gas chromatography with split flame-ionization,
electron-capture detection has been used to detect volatile substances
including methyl bromide in biological fluids. The method offered
economy of time with a sensitivity equivalent to a packed column
(Streete et al., 1992).

2.4.6 Determination of inorganic bromide in air

Analytical methods for the determination of inorganic bromide in air
are not described here as the concentration of bromide is not
specifically related to the amount of methyl bromide in the
atmosphere.

2.4.7 Determination of inorganic bromide in water

Vanachter et al. (1981) carried out bromide determinations in
leaching water using the colorimetric method described by Malkomes
(1970), in which the sample is first heated to dryness, then phenol
red and chloramine-T (sodium p-toluenesulfochloramine) solution
added. After 5 min, the reaction is stopped with sodium thiosulfate.
The resulting blue colour is read on a spectrophotometer at 590 mµ.
The detection limit is 0.1 mg/litre (0.1 ppm).

In another method, water samples were evaporated to dryness at 90
°C. Sulfuric acid, ethylene oxide in diisopropylether, and
acetonitrile were added and the sample shaken. After 30 min, an
aliquot was removed and solid ammonium sulfate added and shaken. After
separation, the upper layer was removed and anhydrous sodium sulfate
added. An aliquot of the dried sample was analysed using GC/ECD
(detection limit 0.01 mg/litre) (Wegman et al., 1981, 1983).

Table 5. Inorganic bromide in plant material/food^a

Medium Sampling method Analytical Detector Detection Comment Reference
method limit

Grain grind samples, add acetonitrile, GLC ECD 0.07 mg/kg not suitable for Heuser & Scudamore
ethylene oxide, and sulfuric fresh vegetables (1970)
acid (4 h, 20 °C); separate
supernatant with ammonium
sulfate; extract with anhydrous
sulfate; supernatant analysed

Salad/ dry samples at 110 °C; grind; GLC ECD 0.1 mg/kg Roughan et al.
vegetables add NaOH, ethanol; evaporate (fresh mass) (1983)
to dryness; add to ulfuric
acid solution/slurry
acetonitrile and ethylene oxide;
analyse 2-bromoethanol

Vegetables extract sample with aqueous GC ECD 0.5 mg/kg interlaboratory Greve & Grevenstuk
ethanol; ash aliquot of (fresh mass) study (1979)
extract in the presence of
NaOH; treat extract with
ethylene oxide

Cereals, extraction of inorganic bromide GC ECD 1 mg/kg Thier & Zeumer
dried and conversion to 2-bromoethanol (fresh mass) (1987)
fruit, by suspension in aqueous 5 mg/kg
dried ethylene oxide and acidification (dried mass)
vegetablea by sulfuric acid; 2-
bromoethanol partitioned into
ethyl acetate and analysed

Table 5 (continued)

Medium Sampling method Analytical Detector Detection Comment Reference
method limit

Vegetables dried for 3 days and comminuted specific lowest value Basile &
aliquots soaked in alcoholic KOH ion given Lamberti (1981)
and mineralized overnight at electrode 0.1 mg/kg
600 °C; ash homogenized with
diluted NaNO₃; supernatant
analysed

grind sample, shake with water potentiometric ECD 0.1 mg/kg Cova et al. (1986)
(6 h); centrifuge extract measurement
(50 ml) + NaNO₃; evaporate with specific
residue, dissolve in water electrode

Peaches peaches blended with bromide- 0.2 mg/litre Austin & Phillips
NaNO₃ crystals and selective (wet mass) (1985)
water; centrifugation electrode
supernatant

Cereals, ground/minced; dried X-ray 5 mg/kg Love et al. (1979)
nuts, 100 °C (18 h), ground fluorescence
spices, powdered sample with boric spectroscopy
fruit acid-sodium sulfate

Grain macerated grain refluxed thiosulfate lowest value Urga (1983)
in ethanol-ethanolamine; titration given
alkali digested; ashed (600°C); 4.5 mg/kg
water extraction; oxidized
with sodium hypochlorite

Table 5 (continued)

Medium Sampling method Analytical Detector Detection Comment Reference
method limit

Vegetables fresh sample homogenized and HPLC UV 4 mg/kg pH of the mobile Van Wees et al.
macerated with water then (205 nm) phase must be (1984)
homogenate centrifuged; adjusted to 5.0
supernatant filtered and the (at higher pH,
filtrate used for analysis e.g., 6.0-6.5, an
overlap between
Br^- peak and
sample interferenaces
may occur)

^a For abbreviations see Table 2.

2.4.8 Determination of inorganic bromide in soils

The colorimetric method of Malkomes (1970) (section 2.4.7) can
also be used for soil. The sample is first sieved, dry-ashed, boiled
in distilled water, and filtered. The filtrate is then analysed.

Brown et al. (1979) determined bromide in soil by extracting with
calcium nitrate solution (0.1 mol/litre) and using a bromide-specific
electrode for detection in the extract. No detection limit was given.

2.4.9 Determination of inorganic bromide in plant material/food

Various methods, such as X-ray spectroscopy, potentiometry,
thiosulfate titration, gas/liquid chromatography, and high-performance
liquid chromatography, have been used to determine bromide content
(section 5.1.4). A summary of methods is given in Table 5.

In the method described by Heuser & Scudamore (1970), bromide ion
is converted into 2-bromoethanol by reaction with ethylene oxide in
acetonitrile-diisopropyl ether, under acidic conditions. The
2-bromoethanol is then determined by gas-liquid chromatography with an
electron-capture detector (ECD). This procedure is suitable for wheat
and maize but is not ideal for salad crops (because of cleaning
procedures) where problems arise, such as severe tailing, lack of
resolution, and poor recovery (Roughan et al., 1983). These authors
varied some conditions, such as preparing the ethylene oxide in
acetonitrile and using Carbowax 20M TPA to prepare the GC column. The
samples (e.g., lettuce) were hydrolysed with alcoholic sodium
hydroxide overnight, ashed for 2 h at 500 °C (600 °C for oily
substances), and ground, prior to digestion with 0.6 N sulfuric acid
(Greve & Grevenstuk, 1976; 1979). Recoveries of 97 % were achieved and
the method was used to determine bromide down to 0.1 mg/kg of
substrate fresh mass (Roughan et al., 1983). A wide range of
vegetables and other crops have been analysed using this method
(section 5.1.4).

A similar procedure for cereals, dried fruit, and vegetables has
been described using GC/ECD (Thier & Zeumer, 1987). The finely ground
sample is suspended in an aqueous solution of ethylene oxide acidified
with sulfuric acid. The inorganic bromide is extracted simultaneously
and converted to 2-bromoethanol. This derivative is partitioned into
ethyl acetate and determined, without further clean up, by electron
capture gas chromatography.

Bromide concentration in plant material has also been determined
by X-ray fluoroscopy with a detection limit of around 5 mg/kg (Brown
et al., 1979; Love et al., 1979).

A specific ion electrode can be used for inorganic bromide
determination using a standard calibration curve with a detection
limit of around 0.1 mg/kg (Basile & Lamberti, 1981; Cova et al.,
1986). Austin & Phillips (1985) used a bromide-selective electrode to
detect levels of bromide ion in peaches; the detection limit for peach
extract was 0.2 mg/litre.

Urga (1983) used a thiosulfate titration method: the macerated
grain was refluxed in ethanol-ethanolamine mixture, and then ashed
(600 °C). The bromide ion was extracted with water and determined by
oxidizing with sodium hypochlorite solution. This was titrated with
sodium thiosulfate, using starch solution as indicator. The lowest
level measured was 4.5 mg/kg.

A quick screening method for inorganic bromide in vegetables,
using high-performance liquid chromatography (HPLC) with a detection
limit of around 4 mg/kg, was described by Van Wees et al. (1984).

2.4.10 Determination of inorganic bromide in urine, blood/
serum/plasma

Various methods for the determination of bromide in biological
fluids have been described: colorimetry (Kisser, 1967), X-ray
fluoroscopy (Rapaport et al., 1982; Shenberg et al., 1988), neutron
activation analysis (Heurtebise & Ross, 1971; Ohmori & Hirata, 1982),
ion-sensitive electrode (Angerer, 1977, 1980); and headspace GC with
FID (Yamano et al., 1987). Koga et al. (1991) compared headspace GC
and an ion chromatography coupled with a conductivity detector to
evaluate levels of bromide ion in urine. GC was more sensitive with a
detection limit of 0.04 mg/litre. Honma et al. (1985) used an GC/ECD
method for their studies on rats (section 6.2). A summary of methods
is given in Table 6.

In forensic science studies (overdose of bromide-containing
sleeping tablets as well as suspected methyl bromide poisoning),
colorimetric methods, such as that of Kisser (1967), have been
routinely used (Weller, 1982). For routine occupational studies, other
methods are more suitable.

Table 6. Determination of bromide in biological fluids and tissues^a

Medium Sampling method Analytical Detection Comment Reference
method limit

Urine/ add soda solution; evaporate + chloramine - - Kisser (1967)
blood and ash (550°C); ash + water T-solution, sodium
->filter filtrate->bromide thiosulfate

Urine alkali ashing (Kisser, 1967); ion-sensitive 1 mg/litre suitable for Angerer (1977,
with KMnO₄, bromide->bromine; electrode occupational 1980)
bromine + sulfide soln->bromide exposure studies

Urine headspace; methylation GC 0.4 mg/litre 2.7% standard Koga et al. (1991)
with dimethylsulfate deviation

Urine ion chromatography 1.0 mg/litre 8.7% standard Koga et al. (1991)
deviation

Serum X-ray fluorescence 0.05 µg Rapaport et al., (1982);
Shenberg et al. (1988)

Urine, neutron activation not given Heurtebise & Ross
saliva, analysis (1971)
serum,
plasma

Serum/ neutron activation 120 µg/g; 4 µg/g occupational Ohmori & Hirata
hair analysis (estimated) studies (1982)

Plasma head space plasma + water + GC/FID 0.5 mg/litre Yamano et al. (1987)
dimethylsulfate (Br^-->
methyl bromide)

^a For abbreviations see Table 2.

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1 Natural sources

The atmospheric levels of methyl bromide are controlled by the
amounts from natural and anthropogenic (man-made) sources and by the
atmospheric and surface removal processes. Observational data (UNEP,
1992) indicate that the current best estimate for the globally
averaged abundance of methyl bromide in the troposphere is between 9
and 13 pptv, which is equivalent to a total atmospheric loading of
150-220 million kg. If the atmospheric lifetime of methyl bromide is
two years, i.e., only tropospheric removal by reaction with OH - is
significant, then a total emission of about 75-110 million kg per year
is required to maintain the observed atmospheric level. However, if
the atmospheric lifetime is only one year (assuming surface removal
comparable in magnitude to the atmospheric removal), a global emission
of 150-220 million kg per year is required to maintain the atmospheric
methyl bromide at the same level (UNEP, 1992).

Khalil et al. (1993) have used similar input data (global
abundance of 10 pptv, lifetime of two years) to calculate a global
source of about 100 million kg/year. On the basis of their
measurements of ocean abundance and supersaturation (which differ
considerably from those of Singh et al. (1983)), they estimated an
ocean source of 35±5 million kg/year. They proposed that the
anthropogenic sources must be about 30 million kg/year, assuming that
the differences in calculated emissions for the northern and southern
hemispheres are solely due to man-made sources. This leaves about 35
million kg/year of emissions that cannot be categorized but are
believed to originate from the tropics.

From the surface water and air observations of methyl bromide
concentrations off the Pacific coasts of North and South America,
Singh et al. (1983) estimated the total natural emissions of methyl
bromide from the oceans to be 300 million kg/year. The total oceanic
emission quantified from the extrapolation of the limited data may not
be entirely justifiable. Using the currently accepted global
atmospheric loading of 150-220 million kg, a tropospheric lifetime of
6-9 months can be expected, meaning surface removal processes are even
more important than reaction with OH. It would also mean that
fumigation sources of methyl bromide are less than 10% of the total
global emission.

It is likely that the calibration standards of Singh et al.
(1983) were in error, leading to overestimation of methyl bromide
concentrations by a factor of about two. Corrections for this factor
would resolve part of the discrepancy between the estimates of Khalil
and Singh of the oceanic source. However, an unresolved difference in
supersaturation measurements (140% and 180% from two Khalil voyages
and 250% from Singh) leaves a conflict of about a factor of three that
cannot be resolved without more measurements.

In any event, the natural/anthropogenic balance of methyl bromide
emissions is very uncertain.

The major natural sources of methyl bromide are considered to be
oceanic biological processes (mainly algal), but the mechanism for the
production of methyl bromide in the marine environment, and its
oceanic distribution, are not well understood (Rogozen et al., 1987;
WMO, 1992).

Methyl bromide occurs naturally in coastal waters together with
methyl chloride and methyl iodide (Lovelock, 1975). This author
suggested that methyl iodide produced by large kelp, such as
Laminaria , reacts with the chloride and bromide ions in sea water
to produce methyl chloride and methyl bromide, respectively.

Harper (1985) reported the formation of methyl bromide from
cultures of a common wood-rotting fungus (Phellinus pomaceus) in the
presence of sodium bromide solution, with cellulose as the substrate.

3.2 Anthropogenic sources

Anthropogenic sources, primarily soil fumigation, add to the
amount of methyl bromide in the atmosphere. The amount released
depends greatly on the regulations, methods used, dosage, type of
plastic cover, length of covering, and precautions taken by the
fumigators. The portion released is a question of dispute. Daelemans
(1978) calculated that 70-90% of the applied amount of methyl bromide
(50-100 g/m²) disappeared into the atmosphere. Using a common
application method (15-25 cm injection with a 2-day cover), analysis
predicted emissions ranging from 45 to 53% (UNEP; 1992). In contrast,
Rolston & Glauz (1982) estimated that 70% of the applied methyl
bromide escaped into the atmosphere after fumigation using injection
chisels.

During structural fumigation, up to 90% of the applied methyl
bromide was estimated to escape into the environment (Reichmuth &
Noack, 1983). During storage fumigation, an estimated 30% of the
methyl bromide may escape from the fumigation chamber and enter the
environment, while the rest decomposes to organic bromine and
methylated derivatives of organic compounds (National Academy of
Science, 1978). Other estimates give an 80% loss of methyl bromide
used on perishable products (UNEP, 1992).

On the basis of the inventory of use and emissions coupled with
the analyses of Singh & Prather (UNEP, 1992), the current best
estimate for total anthropogenic emissions of methyl bromide is about
30 thousand tonnes per year, representing 25±10% of the total
emissions.

Methyl bromide is also emitted from motor vehicles using leaded
petrol (section 3.2.3).

Methyl bromide is listed as a controlled substance in the
"Montreal Protocol on Substances that Deplete the Ozone Layer".

3.2.1 Production levels and processes

3.2.1.1 Producers and world production figures

The total annual methyl bromide sales for the years 1984-90,
tabulated according to region, are shown in Table 7; production
figures for this period were almost identical. In Table 8, methyl
bromide sales are tabulated according to use. These figures were
provided by companies reporting to the Methyl Bromide Industry Panel,
Chemical Manufacturers Association in February, 1992.

Table 7. Methyl bromide sales (tonnes) according to region for 1984-90^a,b

Year North South Europe North Afica Asia Australia Total sales
America America Africa

1984 19 659 1 389 11 364 183 1 595 10 678 704 45 572
1985 20 062 1 503 14 414 45 1 975 9 743 531 48 273
1986 20 410 1 775 13 870 380 2 205 11 278 538 50 445
1987 23 004 1 820 15 359 385 1 751 12 816 555 55 690
1988 24 848 2 058 17 478 277 1 582 3 555 812 60 610
1989 26 083 1 701 16 952 618 2 075 14 386 755 62 570
1990 28 101 1 621 19 119 432 1 838 14 605 928 66 641

Total 162 167 11 866 108 556 2 320 13 021 87 061 4,823 389 814

^aCompiled by the Methyl Bromide Industry Panel, Chemical Manufacturers Association
(unpublished report, February 1992).
^bThe 1990 production figures from other producing countries (e.g., India, China, former
USSR) is estimated to be about 2500 metric tonnes.

Table 8. Methyl bromide sales (tonnes) according to use category for 1984-90^a

Year Pre-plant Post harvest Structural Residential/ Chemical Total sales
commercial intermediates

1984 30 408 9 001 1 285 881 3 997 45 572
1985 33 976 7 533 1 274 983 4 507 48 273
1986 36 090 8 332 1 030 999 4 004 50 455
1987 41 349 8 708 1 763 1 160 2 710 55 690
1988 45 131 8 028 1 910 1 737 3 804 60 610
1989 47 542 8 919 2 083 1 530 2 496 62 570
1990 51 306 8 411 1 740 1 494 3 693 66 644

Total 285 802 58 932 11 085 8 784 25 211 389 814

^aCompiled by the Methyl Bromide Industry Panel, Chemical Manufacturers Association (unpublished
report, February 1992).

The following is a list of the companies, including any related
subsidiaries and/or joint ventures that reported production and
release data:

1. Association of Methyl Bromide Industry Japan (Japan)

(a) Sanko Kagaku Kogyo Co. Ltd

(b) Teijin Chemicals Ltd

(d) Dohkal Chemicals Co. Ltd

(e) Nippon Kayaku Co. Ltd

(f) Ichikawa Gohsei Chemical Co. Ltd

2. Atochem S.A. (France)

(a) Derivados Del Etilo, S.A. (Spain)

3. Dead Sea Bromine Group

(a) Dead Sea Bromine (US)

(b) Eurobrom B.V. (The Netherlands)

4. Ethyl Corporation (US)

(a) Ethyl S.A. (Belgium)

5. Great Lakes Chemical Company (US)

(a) Great Lakes Chemical (Europe) Ltd (UK)

6. Societa Azionaria Industria Bromo Italiano (Italy)

According to Eurobrom B.V. (personal communication), Atochem is
the sole producer of methyl bromide in Europe. Methyl bromide is also
imported into Europe from the USA and Israel (Ethyl Corporation and
Dead Sea Bromine Group).

The average rate of increase in total world sales between 1984
and 1990 was about 6% per year, more than 90% of these sales being in
the Northern Hemisphere. Of the 51.3 thousand tonnes used as a
pre-planting fumigant in 1990, about 80% was used in Europe and North
America.

3.2.1.2 Production processes

Methyl bromide is commonly produced by the interaction of
methanol (CH₃OH) and hydrogen bromide (HBr). The hydrogen bromide
can be generated in situ from bromine and a reducing agent, such as
sulfur or hydrogen sulfide (Dagani et al., 1985). Methyl bromide is
distilled from the reactant mixture and the crude product purified by
further low-temperature fractional distillation (National Academy of
Science, 1978). Another method is to add sulfuric acid to a
concentrated sodium bromide and methanol solution (National Academy of
Sciences, 1978; Stenger, 1978).

Ethyl Corporation and Great Lakes Chemical Co. both use a
coproduction process that produces methyl bromide as a coproduct with
the production of tetrabromobisphenol A (TBBPA). In this process,
bisphenol A (BPA) is dissolved in methanol and then reacted with
bromine to yield TBBPA and hydrobromic acid. The hydrobromic acid
reacts with the methanol to yield methyl bromide (Ethyl Corporation,
Personal communication to the IPCS, 1990).

In the manufacturing process of a Japanese plant, bromine is
first mixed with methyl alcohol and heated at 60-80 °C in a boiler.
The methyl bromide produced is cooled, purified, and condensed. These
processes are mainly conducted in a closed system (Kishi et al.,
1991).

3.2.1.3 Losses to the environment during normal production

In 1973, the emission of methyl bromide from manufacturing
processes in the USA was estimated to be 100 000 kg compared with 11.3
million kg emitted when used as a fumigant (National Academy of
Science, 1978).

However, in 1990, in the USA, the total reported emission of
methyl bromide from industry was 1000 kg (US EPA Toxic Release Index,
1990). In general, because processes are enclosed, the amount of
methyl bromide lost during manufacture is negligible compared with the
amount released to the atmosphere when it is used as a fumigant.

3.2.1.4 Methods of transport

Methyl bromide is easily liquefied and is shipped in steel
cylinders as a liquefied gas under its own vapour pressure (Matheson
Gas Data Book, 1980). This may be augmented with nitrogen or carbon
dioxide before shipment to permit rapid ejection at low temperatures
(Stenger, 1978). Methyl bromide is also transported in cans and tanks.

An industrial code of practice for the handling and
transportation of methyl bromide in Europe has been recommended (EMBA,
1988).

3.2.1.5 Accidental release or exposure

Incidents of methyl bromide poisoning occur through accidental
exposure to the compound, particularly during soil or structural/space
fumigation and also during manufacture (section 9).

3.2.2 Uses

Methyl bromide is used as follows: soil (pre-planting) fumigation
(77%), quarantine and commodity fumigation (12%), structural
fumigation (5%), and chemical intermediates (6%) (UNEP, 1992) (Table
8).

The general use of methyl bromide in fire extinguishers has been
abandoned as it was the cause of a number of fatal accidents (see
section 9). However, it is still used for special-purpose fire
extinguishers (Matheson Gas Data Book, 1980).

Since 1960, methyl bromide has been used as a fumigant for a wide
range of stored, dry foodstuffs and other products, such as tobacco,
fresh fruit, and vegetables, in particular to comply with quarantine
regulations (Bond, 1984). It is used pre-harvest in glasshouses and in
the open as well as post-harvest in mills and warehouses. It is also
used to fumigate buildings, furniture, books, and archived material
(Alexeeff & Kilgore, 1983).

The techniques used for the different types of methyl bromide
fumigation are given in Table 9.

3.2.2.1 Soil fumigation

The gas is a soil fumigant for the control of weeds, weed seeds,
nematodes, insects, and soil-borne diseases (Meister, 1985). Methyl
bromide can be applied to soil under sheeting in a vaporized form
using either evaporating jars (cold method) or heating (hot method),
or injected as a liquid and allowed to vaporize in situ (Table 9).

Table 9. Outline of methyl bromide fumigation techniques^a

Examples of Fumigation Fumigation Application technique Ventilation of
Type application dosage period methyl bromide residues

1. Space Buildings 0.5-1% 2-3 days Sealing of all openings except one door with Natural ventilation (opening
fumigation (mills, in air plastic foil and adhesive tape; placement of of doors, windows) assisted
factories, (20-40 g/m³) methyl bromide cylinders at selected locations by mechanical exhaust
museums) inside building; opening of cylinders by team ventilation if available
of operators working backwards towards escape
door; sealing of escape door

2. Chamber Dried food 0.8-1% < 1 day Permanently installed delivery systems, Mechanical ventilation:
fumigation products, chamber operated from outside of chamber continuous dilution with fresh
wood volume air in atm. pressure chambers,
(32-40 g/m³) batch dilution cycles in
"vacuum" chambers

3. Fumigation Ducts, bins; 1-2% 1-3 days Sealing of goods/machines under plastic foil Removal of sheeting, natural
with stacked in air or tarpaulins; methyl bromide injection through ventilation
movable goods, pieces (40-80 g/m³) ports via flexible tubing, using (a) hot
delivery of machinery vapour systems (methyl bromide passed through
system heat exchanger in a water boiler), or (b) cold
vapour systems (pressurized cylinders on
trolleys)

4. Surface Soil, compost 50-100 g/m^-2 2-5 days (a) Hot vapour application using perforated Removal of sheeting, latency
fumigation tubing prepared under plastic sheeting; period and/or watering before
(b) liquid methyl bromide injection, truck/ tillage
trailer with cylinders connected to injection
nozzles and reel unfolding plastic sheeting
behind truck; (c) methyl bromide cans place in
puncturing cups underneath sheeting, punched
open by operator walking on the sheeting

^aFrom Guillemin et al. (1990).

The methods practised in various countries differ. In the USA,
methyl bromide is mainly applied by chisel application (injection).
Methods of soil disinfestation used in Belgium, for example, are given
in Table 10. In Israel, both soil fumigation in strips and blanket
(large area) fumigation are widely used (Klein, 1989). The methods
used are the hot gas method and injection method. Strip fumigation is
not as effective as blanket fumigation but, in some circumstances, is
more economical.

Table 10. Soil disinfestation methods and products used in Belgium and their relative importance^a

Physical methods:

- steaming : - sheet steaming/steaming via drain pipes 7%
- vacuum steaming of rockwool substrates 2%
- solarization 0%
- microwave radiation 0%
- ozone 0%

Chemical methods:

- methyl bromide (MB) : fumigation (greenhouse/outdoor) 50%
+ injection (outdoor)
- chloropicrin (CP) : injection (greenhouse/outdoor) 10%
- MB + CP : injection (outdoor) 10%
- metham-sodium : injection (greenhouse/outdoor) 8%
- dazomet : soil mixing (greenhouse/outdoor) 3%
- dichloropropene : injection (greenhouse/outdoor) 8%
- others 2%

^a From: Pauwels (1989).

Not only the method of application but also the type of plastic
sheeting used for covering is important for optimal fumigation
conditions as well as for the safety of the fumigators and reduction
of environmental pollution. Munnecke et al. (1978) showed that using
gas-tight films very high concentrations of methyl bromide reached the
soil, whereas, under low density polyethylene (LDPE) covers, these
concentrations rapidly dissipated. In the Netherlands where extensive
horticulture plays an important economic role, Wegman et al. (1981)
reported that 2 million kg of methyl bromide were being used in
glasshouses each year. De Heer et al. (1983) compared different
plastic films in trials in the main glasshouse district of the
Netherlands. They confirmed that the dose of methyl bromide could be
substantially reduced, without affecting the concentration-time
product in the soil, if gas-tight films were used instead of LDPE.
They emphasized that the reduction of methyl bromide losses depends
greatly on how the films are laid down and wetted and on how the

methyl bromide is distributed under the films. The use of methyl
bromide fo