Methyl bromide

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The insecticidal value of methyl bromide was first reported by Le Goupil (1932) in France. During the 1930s it was widely adopted for plant quarantine purposes because many plants, vegetables and some fruits were found to be tolerant to concentrations effective against the insects concerned. More recently it has been used extensively as an industrial fumigant for stored products, mills, warehouses, ships and railway cars. For this purpose it has now largely replaced hydrogen cyanide. Methyl bromide has also been used as a sterilizing agent, although it has approximately one tenth the activity of ethylene oxide against bacteria and fungi (Bruch, 1961; Richardson and Monro, 1962). Its use for the sterilization of space vehicles in combination with ethylene oxide has been reported by Vashkov and Prishchep (1967). At concentration x time products considerably higher than those needed to kill insects, methyl bromide may also control microorganisms such as Aspernillus spp. and Penicillium spp. in foodstuffs (Majumder, 1954).

Methyl bromide is not as toxic to most insect species as are some other commonly used fumigants, such as HCN, acrylonitrile and ethylene dibromide. Nevertheless, other properties make methyl bromide an effective and versatile fumigant. The most important of these is its ability to penetrate quickly and deeply into sorptive materials at normal atmospheric pressure. Also, at the end of a treatment, the vapours dissipate rapidly and make possible the safe handling of bulk commodities. Another important property is the fact that many living plants are tolerant to this gas in insecticidal treatments. Methyl bromide is nonflammable and nonexplosive under ordinary circumstances and may be used without special precautions against fire.

Because methyl bromide has a comparatively low boiling point and is not greatly sorbed by many materials, it may be used for low temperature treatments that are not practicable with many other fumigants.

PROPERTIES OF METHYL BROMIDE

Alternative name: monobromomethane

Odour Nil at low concentrations; strong musty or sickly sweet at high concentrations
Chemical formula CH3Br
Boiling point 3.6C (38.5F)
Freezing point -93C
Molecular weight 94.95
Specific gravity gas (air=1) 3.27 at 0C
liquid (water at 4C=1) 1.732 at 0C
Latent heat of vaporization 61.52 cal/g
Flammability limits in air Nonflammable (see next page)
Solubility in water 1.34 g/100 ml at 25C
Pertinent chemical properties Powerful solvent of organic materials, especially natural rubber. When pure, noncorrosive to metals. Liquid reacts with aluminium (see text)
Method of evolution as fumigant From steel cylinders under naturalor added pressure. Also dispensed from 1 lb cans or 20 ml glass ampoules
Commercial purity 99.4%

Natural vapour pressure at different temperatures

0C (32F) 690 mm
10C (50F) 1006 mm
Hg 20C (68F) 1390 mm Hg
Hg 25C (77F) 1610 mm Hg

Weights and volumes of liquid

1 lb (avdp) at 0C has volume 261.9 ml
1 US gal weighs 14.44 lb (6.550 kg)
1 Imp gal weighs 17.32 lb (7.856 kg)
1 kg has volume 577.36 ml
1 litre weighs 1.732 kg

Dosages and concentrations of gas in air (25C and 760 mm pressure)

By volume

Weight per volume

Parts per million Percent 1g/m lb/1000 ft
20 0.002 0.08  
50 0.005 0.19  
100 0.01 0.39  
200 0.02 0.78  
257 0.026 1.00  
500 0.05 1.94 0.12
1 000 0.10 3.88 0.24
4 121 0.412 16.00 1.00
20 000 2.0 77.65 4.85

1Ounce per 1000 cubic feet or milligrammes per litre

Treatments of a wide range of commodities may be conducted at temperatures down to 4c, or even lower in some instances.

At normal fumigation concentrations methyl bromide is odourless. This disadvantage is sometimes overcome by mixing it at the time of packaging with a warning gas such as chloropicrin. The chloropicrin usually constitutes 2 percent of the mixture. Possible pitfalls in the use of chloropicrin as a warning agent are discussed under the heading of this fumigant later in this chapter.

Thompson (1966) has published a comprehensive review of methyl bromide as an insecticidal fumigant. Reference may be made to this for additional information on some aspects of the subject not covered in this manual.

TOXICITY

The effect of methyl bromide on humans and other mammals appears to vary according to the intensity of exposure. At concentrations not immediately fatal, this chemical produces neurological symptoms. High concentrations may bring about death through pulmonary injury and associated circulatory failure. The onset of toxic symptoms is delayed, and the latent period may vary between 0.5 to 48 hours, according to the intensity of the exposure and the personal reaction of the patient (von Oettingen, 1955). Contact of the human skin with the liquid or strong concentrations of the gas may cause severe local blistering (Watrous, 1942).

Against insects, methyl bromide appears to exert its principal toxic effect on the nervous system. As in humans, the onset of poisoning symptoms may be delayed, and with many species of insects definite conclusions as to the success of the treatment should be delayed for at least 24 hours. The comparative toxicity of this fumigant to some stored-product insects is given in Chapter 14, Table 16, and has recently been discussed by Hole (1981).

Richardson and Roth (1965) had some success with this compound against snails in military cargoes (see Schedule T). Methyl bromide is also effective against mites (Acarina). For grain mites, see Barker (1967a,b), and for cheese mites Burkholder (1966). In the treatments in which living plants and flower bulbs are tolerant, the eggs of mites may be resistant and repetition of fumigation may be necessary (see Schedules F and N).

FLAMMABILITY

In laboratory experiments with an intense electric spark, it was found that methyl bromide had a range of flammability from 13.5 to 14.5 percent by volume in air (Jones, 1928). This range has been widely quoted in scientific and trade literature, and the impression has been created that methyl bromide may be flammable or explosive under certain conditions in air. However, in the same series of tests it was found that mixtures of this gas with air in any proportions are nonflammable when ignition is attempted with a flame.

Simmons and Wolfhard (1955) also confirmed that mixtures of methyl bromide and air are nonflammable. Methyl bromide has proved successful as a fire extinguisher (Schleichl, 1961; Fenimore and Jones, 1963; Fish, 1964).

It should be pointed out that, in the absence of oxygen, liquid methyl bromide reacts with aluminium to form methyl aluminium bromide. This compound ignites spontaneously in the presence of oxygen. The explosion of a large tank containing methyl bromide was attributed to the reaction of this compound with the aluminium stem of a measuring instrument beneath the surface of the liquid.

Methyl bromide should never be stored in cylinders containing any appreciable amount of the metal aluminium and aluminium tubing should not be used for application of the fumigant.

EFFECT ON PLANT LIFE

Methyl bromide is one of the few fumigants that may be used safely on a wide range of living plants without producing harmful effects. However, there is a limited number of genera, species or varieties of plants susceptible to injury. Before using this fumigant, therefore, careful attention should be paid to the exceptions listed in the schedules given in this manual. Because chloropicrin is phytotoxic, methyl bromide containing this gas as a warning agent should not be used on nursery stock or other living plants.

Seeds

Methyl bromide has been employed as a seed fumigant because of its ability to penetrate into large consignments of sacks and bags. Under some circumstances, however, treatment with this fumigant has resulted in loss of viability. Also, germination may be delayed or the vitality of young plants impaired. Intensive investigations during recent years have disclosed that injury to germination and retardation of growth of seedlings are directly related to abnormally high temperature, dosage of fumigant, length of exposure and moisture and oil contents of the seed (see Schedule S for a full enumeration of seed treatments and literature references). It may be concluded that, if the seeds are dry enough for safe storage and are not subjected to unnecessarily high temperatures, the dosages and exposure periods given in this manual will be adequate for insect control and will not be likely to cause much damage to the seed. Blackith and Lubatti (1965) laid down a useful general maxim for methyl bromide: "If the seed is dry enough to store, it is dry enough to fumigate." They kept cereal seeds which had been fumigated at 8, 11, 14, and 18 percent moisture content for six years. The seeds were stored at 20C and at the same moisture content at which they were fumigated. Germination tests were made after 6 months, 3 years and 6 years. For the most part good survival was recorded for both fumigated and nonfumigated seeds at the two lower moisture contents. Rye retained its viability for 3 years when stored dry, but both treated and untreated rye showed almost complete loss of -termination after 6 years.

Powell (1975) tested the tolerance of 40 varieties of vegetable, cereal, fodder and grass seeds with methyl bromide ( c x t products of 200 and 400 mg h/l at 10 and 18C and 10, 13 and 16 percent moisture content) and he concluded that, although the lower values of dosage, temperature amd moisture resulted in better germination, most seeds could be safely fumigated at moisture contents below 13 percent and in many cases up to 16 percent. Treatment of vegetable seeds with mixtures of methyl bromide and carbon dioxide and under partial vacuum likewise had no detectable effect on germination (Kononkov et al, 1979).

Repetition of fumigation on a given lot of seed should be avoided, if possible; it has been shown that more than one fumigation may cause reduction in percentages of germination (Strong and Lindgren, 1961). Repeated fumigation can also have adverse affects on the subsequent growth and yield of plants grown from the treated seeds. In tests on white and yellow maize, Joubert and Du Toit (1969) reported that all treatments caused significant reduction in yields from white maize and that, while the apparently hardier yellow maize showed little effect at time of germination, there was a significant reduction in yield after the second and third fumigation.

If repeat fumigation is considered, it is suggested that germination and possibly growth tests be made to determine if injury has occurred during the first treatment. Joubert and Du Toit (1969) advocate extreme caution with the application of fumigants to seed and they further suggest that a contact insecticide having no adverse effect on the seed should be considered instead of fumigation.

Growing Plants

Methyl bromide may be used to fumigate some growing crops to control pest organisms. The development of light-weight plastic sheets has made it possible to cover sizable areas of land so that the fumigant can be contained for sufficient time to effect a treatment. Large beds of strawberry plants infested with cyclamen mite have been successfully treated in this way (Allen, 1957) and methods for control of European pine shoot moth on ornamental pines have been described (Carolin et al, 1962; Klein and Thompson, 1962; Carolin and Coulter, 1963).

It is estimated that nearly 95 percent of the nursery stock and other plants being moved in commerce are tolerant to dosages of methyl bromide that will kill the insects or other pests involved (Richardson and Balock, 1959). In a few genera of plants, all species may be intolerant while in others only a few species or varieties are known to be affected. Latta and Cowgill (1941) tested 441 species of glasshouse plants with methyl bromide and found that 414 (93.9 percent) were not injured and 27 (6.1 percent) sustained varying degrees of damage; of those, five species were severely burned. In tests on improved citrus stock, Riviello and Rhode (1976) found that exposure to 16 mg/l for 2 hours at 25 - 30C and 90 percent RH for control of citrus black fly caused little damage to tender growth. A Handbook of Plant Tolerances to Methyl Bromide has been compiled by USDA (1977).

There are several factors that influence the unfavourable response of growing plants to methyl bromide; if they are avoided, even fairly susceptible varieties will be tolerant or, at worst, only lose foliage that will be replaced by new growth. The most important adverse factors are as follows:

1. Low humidity during treatment. Relative humidity in the chamber should be held above 75 percent during fumigation.

2. Dry soil around roots. Less damage is sustained if the soil is moist, mainly because the roots are less susceptible to injury. If there are no insects to be controlled in the soil, it may be completely drenched. Waterlogged soil will not permit the penetration of methyl bromide, and sometimes it is desirable to protect the roots in this way. On the other hand, moist soil allows the rapid penetration of the fumigant.

3. Excessive air currents during fumigation, or during the posttreatment aeration period, aggravate injury. It is recommended that circulating and ventilating fans or blowers be operated for the minimum length of time required for distributing the fumigant evenly or for removing toxic concentrations after treatment.

4. Some species of plants may be fumigated only when fully dormant; others are tolerant at any normal stage of growth. The question of dormancy is discussed in the next paragraph and is also covered in Schedules C to F.

Nursery Stock

Plants in active growth are more subject to injury than are dormant plants. As long as plants are fully dormant, there is less danger of damage from methyl bromide, but at the time of breaking dormancy, there may be a period of susceptibility to injury. Coniferous evergreens are particularly liable to sustain severe damage at this critical stage. Great care must be exercised in the choice of the time for nursery stock treatments.

It should be borne in mind that while the failure of subsequent growth of treated plants or any other injury may be attributed to the fumigation treatment, it may also be caused by handling or shipping, as demonstrated by Gammon (1950) and H.H. Richardson (1951) in imported camellia cuttings. Claims that injury to nursery stock is due to the fumigation process should be investigated closely to ascertain whether some other factor or combination of factors may not be responsible.

Recommended treatments for this fumigant on nursery stock are given in Schedules E and F.

Flower Bulbs

Methyl bromide may be used to fumigate narcissus and other bulbs to control insects such as the greater and lesser bulb flies. The treatments effective against these pests do not injure the bulbs (Mackie et al, 1942; Andison and Cram, 1952).

This fumigant is also effective against bulb mites. However, the eggs are resistant to methyl bromide and treatments which are strong enough to kill the eggs are completely destructive to the bulbs. For complete control, the regular treatments may be repeated after 10 to 14 days or when the eggs have hatched. The repetition of the mild treatment causes no injury to the bulbs (Mackie et al, 1942; Monro, 1937-40). Purnell and Hague (1965) reported that fumigations with methyl bromide effective against the stem nematode (Ditylenchus dipsaci Kuhn) are injurious to narcissus bulbs.

The recommended treatments are summarized in Schedule N.

EFFECT ON PLANT PRODUCTS

Fresh Fruit

Methyl bromide has been used widely for quarantine fumigations of fresh fruit. It has been found that some fruits, or certain varieties, are susceptible to injury. The differences in varietal susceptibility are particularly noticeable in apples (Phillips et al, 1938; Phillips and Monro, 1939; Sanford, 1962b; Richardson and Roth, 1966). External damage often takes the form of brown lesions or small round spots on the skin caused by increased or decreased pigmentation in the normal colour of the fruit. Internal injury appears usually as browning of the tissue. With some fruit, ripening and pigmentation are stimulated by low dosages and retarded by high ones. Fruit may vary in susceptibility from one season to another; this is believed to be due to variations in the physiological condition of the fruit. Some workers have been able to detect slight off-flavours or lessening of flavours in fruit subjected to methyl bromide, but it is unlikely that these would be easily detected by the public to the extent that marketing would be affected. The tolerance of deciduous fruit to methyl bromide and other fumigants is discussed fully by Claypool and Vines (1956).

While some fruits are susceptible to injury by methyl bromide, others are tolerant and are treated with this fumigant in quarantine procedures. Methyl bromide is particularly useful when treatments at low temperatures are required. Details of treatments for tolerant fruit are given in Schedule H. It is recommended that fumigation of fruit with methyl bromide should not be carried out on a commercial scale until careful preliminary experiments have indicated that the particular kinds or varieties concerned are tolerant under the full range of conditions likely to be encountered in practice.

At dosages considerably lower than those needed to kill insects, methyl bromide has been successfully used for killing rats and mice in fruit storage units. With the treatments given in Schedule T (Rodents), injury to fruit is not likely to occur.

Vegetables

Both fresh and dry vegetables are generally tolerant to insecticidal treatments with methyl bromide (Roth and Richardson, 1963, 1965).

Schedule I lists tolerant and susceptible fresh vegetables. This fumigant has been used extensively for the treatment of both early and late varieties of potatoes to control the larvae of the tuber moth Phthorimaea operculella. In treatments with concentration x time (c x t) products of 85 mg in/l, which are completely effective against these insects, tubers of all varieties tested at all stages of maturity have proved to be tolerant (Lubatti and Bunday, 1958). Adults and pupae of the Colorado potato beetle can also be controlled without injury to the potatoes (Bond and Svec, 1977).

Sweet potatoes were found by Phillips and Easter (1943) to be sensitive to insecticidal treatments under some conditions. It was noted that newly harvested sweet potatoes were likely to be severely injured, whereas those cured for 15 days or more or kiln dried at 27 to 30C, were not always injured. Breakdown of cured sweet potatoes after fumigation was associated with postfumigation storage temperatures. Material held at 21 to 27C was affected less than that moved to ordinary storage at lower temperatures. Proper ventilation after fumigation decreased the amount of the breakdown.

Cereals and Milled Foods

Methyl bromide is widely used for the fumigation of almost every type of cereal and cereal product. Because it penetrates densely packed materials, it is especially useful for the treatment of flours and meals (see Schedule P). Although methyl bromide will react with the protein fraction of wheat (Winteringham et al, 1955), a number of studies have shown that a single treatment at recommended dosages has little or no adverse effect on food value or bread making quality. Even repeated fumigation of wheat stored over a 3year period with a total of 8 treatments caused no significant effect on the vitamin B-6 components (Polansky and Toepfer, 1971) or Tocopherols (Slover and Lehmann, 1972). However, there was a gradual increase in inorganic bromide residue and there were some indications of minor changes in physical qualities of bread made from this wheat. Some members of a taste panel detected a stale aroma in laboratory-type breads and crumbly texture in rolls made from wheats exposed to repeated methyl bromide fumigations (Matthews et al, 1970 a, b).

It has been noted that bread made from flour fumigated with excessive dosages of methyl bromide may have a foreign odour, and if the bread is toasted an unpleasant off-flavour may be produced. Occurence of this phenomenon is rare and sporadic; Brown et al (1961) reviewed a number of reports of this taint encountered under commercial conditions and carried out a number of tests in the laboratory and they came to the following conclusion:

"It would now appear that some taint is possible even at dosages normally used commercially for insect control. This tainting usually takes the form of abnormal odours when the hot loaves are removed from the oven.

The taste of the bread when cold is quite unaffected at these levels of treatment but a faint odour may still be detected if the bread has been wrapped in polythene or similar material. The avoidance of taint is made more difficult by the likelihood of uneven distribution of fumigant in many types of treatment. However, the risks become very slight if care is taken to limit the level of treatment, if restrictions are placed on repeated fumigation, and if appropriate dilution of fumigated flour by unfumigated flour is arranged where necessary. Over many years very large tonnages of flour have been fumigated with methyl bromide without difficulty and the number of complaints that have come to light is extremely small. These might have been avoided if the precautions suggested had been followed."

As general precautions in the fumigation of flour with methyl bromide great care must be taken not to exceed recommended concentrations or treatment periods; to ensure that even distribution of the fumigant be effected as quickly as possible after the beginning of the treatment and that aeration of the entire stock be conducted quickly and thoroughly immediately on termination of the treatment.

High moisture content of the flour may also be an important factor, as was suggested by the work of Hermitte and Shellenberger (1947) who, however, used excessive doses of methyl bromide greatly above those used in commercial practice.

The only material under this heading barred from fumigation appears to be full fat soybean flour, in which persistent odours and off-flavours may be produced (Dow Chemical Company, 1957).

Nuts and Shelled Nuts

These are treated regularly with methyl bromide, because they are often best suited for bulk treatment (see Schedule P). An interesting and spectacular practice is the treatment of large pyramids of groundnuts awaiting shipment at collecting points in west Africa (Hayward, 1954; Halliday and Prevett, 1963).

Although neither high residues nor taint are produced by normal treatments, excessive dosages or repetitions of treatment should be avoided. Srinath and Ramchandani (1978) reported some off-flavour in walnuts given a second treatment with methyl bromide and more pronounced effects after a third treatment. Shelled nuts with a high oil content, such as cashews, must be treated with particular care. When nuts are stored for prolonged periods in warm weather, fumigation may be repeated. If it is necessary to apply more than two treatments with methyl bromide, a preliminary fumigation of small samples should be made to determine effects on quality.

The problem of treatment repetition may be encountered with importations. Almost invariably, nuts and shelled nuts are fumigated in the country of origin before export, often with methyl bromide. If more than one fumigation is required after importation, there may be danger of taint and a trial treatment should be made.

Dried Fruit

Methyl bromide has been used extensively in recent years for the atmospheric or vacuum fumigation of dried fruit of all kinds. It is well suited for this purpose because it penetrates densely packed materials and diffuses away rapidly after treatment (Page and Luhatti, 1949; Page et al, 1949).

EFFECT ON ANIMAL PRODUCTS

Dairy Products

Methyl bromide is useful for the treatment of dairy products in storage rooms or in convenient atmospheric chambers. It is effective against the cheese skipper, Piophila cased (L.), cheese mites and the grain mite, Acarus siro L., occurring not only on the cheeses themselves but also in infested stores (Dustan, 1937; Robertson, 1952; Searls et al, 1944; Burkholder, 1966). Incidental pests, such as cockroaches, are also easily controlled. Residues in cheese, skim milk powder and butter are generally low. Suggested treatments are given in Schedule P.

Dried Fish and other Animal Products

Calichet (1960) reported that methyl bromide may be user, effectively to control outbreaks of Dermestes beetles in dried fish under African conditions. Similarly, baled animal skins in freight container, have been disinfested with this fumigant (Wainman et al, 1980).

EFFECT UN MISCELLANEOUS MATERIALS

The fumigation of some foodstuffs with methyl bromide may result in the creation of undesirable taints or odours. In some instances they may be attributed to reactions with sulphur or sulphur compounds originally present or added during processing. These odours usually persist intirefinitely and in most cases there is no practical way to remove them. Some of the susceptible naterials are not likely to be encountered in strictly agricultural applications of fumigation, but they are listed here so that trouble with them may be avoided.

The following materials should not be expose,) to methyl bromide, or should be exposed only after conducting preliminary tests with small samples (Dow Chemical Company, 1957):

- iodized salt, stabilized with sodium hyposulphite;

- certain baking sodas, salt blocks use d for cattle licks or other foods containing reactive sulphur compounds;

- full fat soya flour;

- sponge rubber

- foam rubber as used in rug padding, pi I lows, cushions and mattresees;

- rubber stamps and similar forms of reclaimed rubber;

- furs, horsehair and pillows ( especially feather piIlows);

- leather goods, particularly white kid or any other leather goods tanned with a sulphur process;

- wool lens, especially angora; some adverse effects have been noted on woollen socks, sweaters and yarn;;

- viscose rayons, made by a process that uses carbon disulphide;

- cinder blocks or mixtures of mortar; mixed concrete occasionally picks up odours;

- charcoal, which not only becomes contaminated but sorbs great amounts of methyl bromide and thus reduces effective fumigant concert rations;

- paper that has been cured by a sulphide process and silver polishing papers;

- photographic chemicals, not including cameras or films;

- rug padding, vinyl, cellophane;

- any other materials that may contain reactive sulphur compounds.

Methyl bromide decomposes into hydrobromic acid, among other products, in the presence of a flame; this acid is extremely corrosive to metals and destructive to plants.

Where heat is required to raise the temperature for fumigation, steam pipes or low temperature electric strip heaters are recommended. Open flame or high temperature electric heaters should NOT he used (maximum temperature limit is 260C).

RESIDUES IN FOODSTUFS

Following fumigation of foodstuffs, the greater part of the methyl bromide is desorbed and diffuses away quickly. Under normal circumstances gaseous methyl bromide does not present a residue problem. However, there is usually a small, variable amount of permanent residue resulting from the chemical reaction between this fumigant and some constituents of the material. The reaction profioct, which is usually easily detectable, is inorganic bromide. In considering this subject it must be borne in mind that many foodstuffs contain natural ly occurring bromides ( Heywood , 1966) .

Bromide residues are not likely to he important from the point of view of human health if the foods containing them are consumed in normal amounts. For example, it would require about 135 kg (over 300 lb) of fumigated apples to furnish the average merdicinal dose of bromide salt (Phi I I ips et al, l938). However, residues in fumigated nuts much greater than in fruit and vegetables anti problems with flavour or odour can occur. An off-flavour can develop in mesh, bromide-treated nuts upon roasting even though, in some cases, the recommended treatment is followed (Bills et al, 1969). The sequence of events leading to the production of an off-flavour occurs in two steps: first, methyl bromide reacts with methionine in the nuts and second, when the nuts are roasted the product breaks down to release dimethyl sulphide - an odorous sulphur compound. The best way to avoid the problem is through the judicious use of methyl bromide as a fumigant. To ensure that unrousted nuts have not been over-fumigated with methyl bromide, a simple quality control test can be done by roasting a few ounces of the nuts and checking aroma and flavour.

High levels of methyl bromide residue may be of some significance in animal feeds. Cooper et al (1978) and Griffiths et al (1978) reported an adverse effect on egg flavour and a taint in roasted meat from poultry fed on a diet that had been fumigated at high concentrations to eliminate Salmonellae. The off-flavour may result from formation of dimethyl sulphide during the cooking process.

There is also the problem of what happens to the methyl radical, the other part of the methyl bromide molecule, when the residue is formed. As the result of comprehensive experiments on the fumigation of wheat with methyl bromide, it has been concluded that methylation of the protein fraction of the grain is the principal reaction of the methyl radical (Bridges, 1955). Several subsequent studies have shown broad range methylation of protein and free amino acids in cereals fumigated with methyl bromide (FAD/WHO, 1980). The main site of decomposition of methyl bromide in cocoa beans was shown by Asante-Poku et al (1974) to be the alcohol-insoluble proteins, with the greatest amount of breakdown in the shells. Treatment with methyl bromide leads to no appreciable loss of the essential amino acids (Winteringham, 1955) and, although methyl bromide reacts to some extent with vitamins of the B group, such reactions are of no practical importance because there is no significant loss of these vitamins under the conditions of ordinary methyl bromide fumigation (Clegg and Lewis, 1953; Polansky and Toepfer, 1971).

Lynn (1967), in a comprehensive review of the effect of methyl bromide fumigations with respect to methylation of naturally occurring compounds, summarized the subject as follows:

1. Feeding studies with rats and rabbits provide ample evidence that the overall nutritional quality of food is not affected by methyl bromide fumigation. These data also attest to the absence of a health hazard.

2. The essential vitamin-B group is not affected by methyl bromide fumigation.

3. There are indications that the following compounds might be formed by methyl bromide fumigation:

methionine sulphonium methyl bromide
l-methyl histidine
S-methylcysteine
o-methyl compounds

4.Biochemical work has shown that:

- the methionine analogue is found as A naturally occurring component of foodstuffs, is nutritionally equivalent to methionine from the amino acid standpoint end is effective as a transmethylation agent;

- the histidine analogue is commonly encountered in animal and human metabolism and is handled without adverse effect;

- the cysteine apologue is readily metabolized by animals and humans;

- the o-methyl compounds are commonly encountered and accommodated by the animal organism.

A great deal of work has been done on the inorganic bromide residues formed in foodstuffs as the result of fumigation with this compound. Summarized information and literature references are given in the schedules at the end of this manual under the headings of the various types of foodstuffs treated.

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