Ethylene oxide

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As an insecticide, the principal use of ethylene oxide (ETO) has been for fumigation of bulk grain in recirculating systems and in the vacuum fumigation of packaged foods and tobacco. It has also proved to be effective both under vacuum and at atmospheric pressure for destroying several species of snails entering the United States in military cargoes from the Mediterranean area (Richardson and Roth, 1963), see Schedule T. In recent years, ETO has been used extensively for the cold sterilization of medical supplies and instruments, for preventing spoilage in foodstuffs and spices and also for controlling diseases in honeycombs and equipment from honeybee colonies. For information on the use of ETO for sterilization, reference may be made to the following: Rauscher et al (1957); Mayr and Kaemmerer (1959); Bruch (1961); Mayr (1961); Phillips (1961); Stierli et al (1962); Moeller et al (1972); Cantwell (1975).

FLAMMABILITY

Ethylene oxide is flammable within wide limits. It is therefore necessary in many commercial applications to mix it with a nonflammable carrier. It is obtainable mixed with carbon dioxide in the proportion of one part ETO to nine parts CO2 by weight or lt or 12 percent ETO with nonflammable halogenated hydrocarbon refrigerant gases. The flammability limit of ethylene oxide - methyl bromide - air mixtures is given by Hashigochi et al (1967).

PROPERTIES OF ETHYLENE OXIDE
Alternative names: 1, 2-epcxyethane, oxlrane
Abbreviation used in this manual : ETO

Odour Irritating, mustard-like. May be hard to detect in low concentrations
Chemical formula (CH2)2O
Boiling point 10.7C
Freezing point -111.3C
Molecular weight 44.05
Specific gravity  
gas (air = 1) 1.521
liquid (water at 4C = 1) 0.887 at 7C
Latent heat of vaporization 139 cal/g
Flammability limits in air 3 to 80% by volume
Solubility in water Infinite at 0C
Pertinent chemical properties Highly reactive and flammable; relatively noncorrosive
Method of evolution as fumigant By discharge by natural pressure from gas cylinders. Owing to high flammability, usually mixed 1 : 9 with carbon dioxide.
Commercial purity 99.5%

Natural vapour pressure at different temperatures

0C (32F) 493.1 mm Hg
10C (50F) 738.0 mm Hg
20C (68F) 1 095.0 mm Hg

Weights and volumes of liquid

1 lb (avdp) at 7C has volume 511.4 ml
1 U.S. gal weighs 7.4 lb (3.354 kg)
1 Imp gal weighs 8.87 lb (4.023 kg)
1 kg has volume 1 127.39 ml
1 litre weighs 0.887 kg

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

By volume

Weight per volume

Parts per million Percent g/m lb/l 000 ft
50 0.005 0.09  
100 0.01 0.18  
200 0.02 0.36  
500 0.05 0.90  
555 0.055 1.00  
1 000 0.10 1.80 0.11
8 885 0.89 16.00 1.00
20 000 2.0 36.01 2.25

1 Ounces per 1000 cubic feet or milligrammes per litre

TOXICITY

Despite a general impression to the contrary, ETO must be regarded as poisonous to humans by inhalation, although it is not as lethal in comparatively low concentrations as some other fumigants. The acute toxic effects of ETO in humans and animals include acute respiratory and eye irritation, skin sensitization, vomiting and diarrhoea. Skin injury may result from excessive freezing following spillage of the chemical. Continuous exposure to even low concentrations may result in a numbing of the sense of smell.

Known chronic effects consist of respiratory irritations and secondary respiratory infection, anaemia and altered behaviour. Although limited tests on mice have not revealed carcinogenic effects, the alkylating and mutagenic properties of ETO are sufficient to cause concern (Glaser, 1979). Health authorities recommend that ETO be considered as potentially carcinogenic to humans and that occupational exposure to it should be minimized by eliminating all unnecessary and improper uses. The threshold limit for continuous daily breathing is presently listed by the American Conference of Governmental Industrial Hygienists (ACGIH, 1981) for change from 10 to 5 ppm.

Of the commonly used fumigants, ethylene oxide is about intermediate in toxicity to insects (see Chapter 14, Table 16).

EFFECT ON PLANT LIFE

Ethylene oxide reacts strongly with living plant material, causing either death or extreme injury. It is not usually recommended for use on seeds (Joubert and Du Toit, 1965), nursery stock or any growing plants.

A report by Steinkraus et al (1959) shows that some species of air-dried seeds containing 5 to 10 percent moisture may be tolerant to bactericidal and fungicidal treatments with ethylene oxide.

The tolerant seeds did not lose viability after exposure to pure atmospheres of ethylene oxide for periods up to one hour at 27C. On the basis of the concentration x time (c x t) products, the treatments for 60 minutes would be assumed to be highly insecticidal. The tolerant seeds were onion, aster, mung bean, spinach, lucerne, pea, dandelion, Sudan grass and radish.

Seeds that suffered serious loss of germination were garden bean, pea bean, red kidney bean, carnation, barley, oats, wheat, maize (including sweet corn), mignonette, anchusa and nasturtium. The germination of lucerne seed was seriously impaired by quick dipping or soaking in water before fumigation.

Because this gas is both insecticidal and toxic to some micro-organisms, its use may be especially valuable for the production of disease-free and insectfree seed of the tolerant species. A method for the elimination of microflora from barley kernels with ethylene oxide has been described by Bushnell (1973).

EFFECT ON PLANT PRODUCTS

Fresh Fruit and Vegetables

Although some fresh fruit (blackberries and blueberries) have shown tolerance to ETO in treatments against insects, severe injury occurs to bananas (Osburn and Lipp, 1935) and other fruit and vegetables (Lepigre, 1947). It would be unwise to attempt any treatment of fruit and vegetables with this gas without preliminary experiments.

Cereals and Milled Foods

At atmospheric pressure, ethylene oxide does not penetrate well into bagged and packaged cereals and milled products (Lepigre, 1947). It is used for this type of material mainly in vacuum fumigation. Its use as a fumigant for treating bulk grain by recirculation in silos is discussed in Chapter 10.

Dried Fruit

Ethylene oxide is used in the dried fruit industry to stop microbial spoilage in prunes and, presumably, these treatments are also insecticidal.

EFFECT ON FOODSTUFFS

Ethylene oxide has been used for over 40 years for both insecticidal treatments and for the sterilization of foodstuffs. A number of investigations have shown that it will react with food constituents and disturb the nutritional value of food. Modification of colour, taste, odour and texture of foodstuffs may occur (Kroeller, 1966) but many materials can be fumigated without appreciable change in these properties. Nearly all spices can be fumigated with little or no change; however, slight alteration of colour and taste has been observed in spices such as mustard seed and turmeric (Mayr and Suhr, 1973). The chemical composition of flour has been reported by Koyanagi et al (1963) to show some changes but no marked deterioration in baking quality was found.

Vitamins of the B complex and some of the amino acids may be destroyed when exposed to ETO; however, drier conditions may reduce this effect. Charles et al (1965) found that, in a dry sterilization procedure where the efficiency of the treatment was satisfactory, the effect on vitamin B content was only slight in comparison to steam sterilization.

Although Hawk and Mickelsen (1955) found that the growth rates of rats was restricted when the animals were fed a diet treated with a high level of ETO for 18 hours, feeding trials carried out on rats and mice over several generations (Charles et al, 1965) showed that animals fed a diet treated for eight hours, with subsequent complete aeration, had the same growth rates and litter sizes as those on untreated diets. Sterilization procedures for various diets for laboratory animals, including fish, have also been developed (Ready et al, 1968; Trust and Wood, 1973).

RESIDUES IN FOODSTUFFS

Chemical residues in commodities treated with ETO may occur as follows: unchanged ETO, which may persist for some time after the treatment; compounds of low molecular weight, such as ethylene chlorohydrin, ethylene bromohydrin and ethylene glycol, produced by interaction of LTO with inorganic constituents of the commodity; alkylated and hyrdroxyethylated derivatives of food constituents such as sugars, amino acids, vitamins and proteins.

When treated commodities were kept at 25C, either under air tight storage conditions or in the open air, Scudamore and Heuser (1971) found that residual ethylene oxide usually fell below 1 mg/ky within 14 days; however, flour treated at high levels for sterilization and kept under air tight conditions retained 50-100 my/kg in this time and traces were found after 90 days. At lower temperatures ETO disappeared more slowly. Pfeilsticker and Rasmussen (1974) showed that the fumigant is preferentially bound in the aleuron cells and the embryo of wheat kernels.

The detection of the reaction product ethylene chlorohydrin was reported by Wesley et al (1965) and ethylene bromohydrin was found in flour and wheat previously treated with methyl bromide before ETO (Heuser and Scudamore, 1969a). Levels of ethylene chlorohydrin produced by exposure to ETO ranged from zero in groundouts and cocoa beans treated at insecticidal levels to thousands of parts per million in sterilized curry powder and turmeric. Stijve et al (1976) found that the amount of ethylene chlorohydrin formed in fumigated flour was roughly proportional to the inorganic chloride content, while in other commodities, notably mushrooms, it was much less. The persistence of ethylene chlorohydrin varied considerably with the type of food; dehydrated mushrooms lost 7080 percent within 4 months whereas no decrease was observed after the same period in black pepper and whole turmeric. In the preparation of baked and steamed products from flour containing ethylene chlorohydrin and ethylene bromobydrin, Scudamore and Heuser (1971) found that 20 to 100 percent of the residue was lost, depending on the alkalinity of the material.

Using radioactive ETO, Pfeilsticker and Rasmussen (1974) found that 85 percent of the bound fumigant in wheat was converted to water-soluble compounds. The radioactivity was distributed among various substarices, including proteins, organic acids, saccharides, lipids and starch. A method for determination of ethylene chlorohydrins in foods was outlined by Ragelis et al (1966) and one for the identification of 2 - chloroethyl esters of fatty acids in spices and foods was given by Heike and Griffitt (1979).

Scudamore and Heuser (1971) concluded that residual amounts of ETO and glycols in foodstuffs after fumigation are unlikely to constitute a hazard and that the ethylene chlorohydrin formed in otherwise significant amounts may partly disappear during storage and cooking.

METHODS OF ANALYSIS

Determination of Vapours

For field use the sachet method of Heseltine and Royce (1960, see Chapter 4) may be used to indicate the attainment within limits of 10 percent of required concentration x time (c x t) products, with the aid of a simple titration conducted on the spot. There are also available on the market indicator tapes for sterilization with ETO but apparently there is no record of them having been used for insecticidal fumigations.

Richardson and Roth (1963) found that the thermal conductivity analyser could be used in practical fumigations for the ethylene oxide-carbon dioxide mixture. They describe their procedure in detail. With heavy loads of sorptive material, which remove ETO from the atmosphere but do not take up CO2, the method was not sufficiently accurate for a close control of ETO concentrations. Used in conjunction with the sachets of Heseltine and Royce (1960), however, these authors found that the thermal conductivity analyser could be used effectively in certain field applications. Detector tubes, described in Chapter 4, give good readings for ETO in insecticidal concentrations. The presence of CO2 made no difference (Dumas and Monro, 1966).

Methods for monitoring exposure to ethylene oxide in the occupational environment have been described by Qazi and Ketcham (1977) and Romano and Renner (1979).

Determination of Residues

The standard method for determination of residual ETO vapours in foodstuffs is that of Lubatti (1944). This is based on bubbling the atmosphere under test through dilute sulphuric acid solution containing a high concentration of magnesium bromide. Ethylene bromohydrin is formed and sulphuric acid is consumed in the process. The unused acid is titrated with standard sodium hydroxide solution to indicate the amount of ETO consumed by the acid. This method has been further developed by Hollingsworth and Waling (1955) and also by Benedict (1957), who described a simplified procedure for determining the residual ETO in fumigated copra.

The employment of the technigues of yes chromatography has been reported by Kalinenko and Naimushin (1961), Berck (1965a), Staszewski, et al (1965), Gafarova, et al (1966) and Dumas (1976). A comparison of analytical methods for residual ethylene oxide analysis was given by Romano and Renner (1979).

APPLICATION

For use as an insecticide, this fumigant is usually marketed in steel cylinders containing 30 or 60 lb (14 or 28 kg) of the 1 : 9 mixture with CO2. For some applications in specially designed equipment, under expert supervision, there is also available a mixture of 90 percent ETO and 10 percent CO2. At normal temperatures, the 1 : 9 mixture in the cylinder exerts a pressure of about 80 atmospheres. In vacuum fumigation, the cylinder containing the mixture is sometimes first discharged into a large storage tank or "accumulator" where it is warmed up before being introduced into the evacuated Fumigation chamber. The object of this step is to provide a homogeneous mixture in the fumigation system from the beginning of the treatment.

For use as a sterilizing agent, ETO is available as an aerosol mixed with propellants of the Freon type. Ethylene oxide constitutes 11 percent of the mixture and may be discharged from the container without the risk of fire or explosion.

For insect control in foodstuffs fumigated under vacuum, a usual application rate is 100 g/m for three hours at temperatures between 20 and 25C and for sterilizing foodstuffs, 500 g/m for six hours at similar temperatures.

PRECAUTIONS

Fire and Explosion Hazards

Unless special precautions are taken, there is danger of fire or explosion when ETO is being used. An explosion of the 1 : 9 mixture (ETO : CO2) may be caused by a static spark generated while the gas mixture is passing through a metal tube on its way from the cylinder to the chamber. Therefore, precautions must be taken against the building up of static electricity, by earthing all equipment.

Protection of Personnel

Protection against the inhalation of ETO is afforded by a respirator fitted with a standard "organic vapours" canister, as long as the concentration of the fumigant does not exceed 2 percent by volume. It must be remembered, however, that the canister does not protect against inhalation of CO2 which, at high concentrations in air, may rapidly produce giddiness and suffocation. This is due not only to the direct action of CO2 on the respiratory centres, but also to the reduction of the oxygen content of air by the presence of excess CO2. For instance a dosage recommended for atmospheric fumigation chambers is 400 g/m (25 lb/1000 ft) for 12 to 24 hours. The atmosphere in an empty chamber would thus contain 2.2 percent ETO and 19.8 percent CO2. Selfcontained respirators or continuous flow air-line respirators that supply breathing air for prolonged periods in hazardous atmospheres may be useful in such situations.

In the normal use of ETO in confined spaces, such as grain silos and fumigation chambers, the chances of exposure to high concentrations of ETO sad CO? are slight. Because the respirator cannot be relied upon to give protection against the mixture, attempts should not be made to enter places containing full fumigation concentrations, except in cases of extreme emergency. Under such circumstances, an air-line hose mask or self-contained breathing apparatus should be used.

Ethylene dichloride

Ethylene dichloride (EDC) is not as toxic to insects as other commonly used fumigants, but it is useful in the fumigation of grain and seeds. Because both the vapours and the liquid are flammable, EDC is mixed with some nonflammable material, usually carbon tetrachloride (CT) in the proportion of three parts EDC to one part CT by volume. The mixture, applied according to recommendations, has no adverse effect on the germination of seeds or the milling qualities of grain (Cotton, 1963). Care must be taken to avoid excessive exposure (Caswell and Clifford, 1958). Although some plants appear to be tolerant to EDC, severe injury has been recorded with certain species. Some fruits are also tolerant (Claypool and Vines, 1956). This fumigant, therefore, should not be used alone or in a mixture for fumigating nursery stock, living plants or vegetables without careful preliminary experiments on the particular species or varieties concerned.

EDC has been used in emulsion with water against the peach tree borer when soil temperatures were too low for effective use of paradichlorobenzene (Snapp, 1939). Some injury has been reported to peach trees.

Because EDC is soluble in fats and oils, it is not recommended for use on cereals or foods with a high oil content.

TOXICITY

Ethylene dichloride has the property of causing injury to the human liver and kidney from either excessive single or repeated exposures. Acutely, it is somewhat more toxic than carbon tetrachloride and under these conditions is also a central nervous system depressant and lung irritant. Recent research has shown that high dosage levels of EDC can cause tumours in rats and mice (National Cancer Institute, 1978) and this observation has led some countries to regulate the use of EDC so that adequate precautions against accidental exposure may be taken.

In practice, most people will not tolerate or will be nauseated by sublethal concentrations (see the section on precautions below).

Information on the toxicity of EDC to insects is given in Chapter 14 (Table 16).

RESIDUES IN FOODSTUFFS

During fumigation of cereal grains with ethylene dichloride or its mixture with other halogenated hydrocarbons, relatively heavy and continuous sorption of the fumigant takes place (Winteringham, 1944). The amount sorbed is higher at lower temperatures. The adsorbed fumigant airs off slowly from whole grains over a period of months. During handling, cleaning or milling processes, the amount of adsorbed fumigant is progressively reduced (Lynn and Vorhes, 1957). After milling, a greater proportion of ethylene dichloride is found in the bran than in the whole grain before milling (Conroy et al, 1957).

PROPERTIES OF ETHYLENE DICHLORIDE
Alternative name: 1, 2 dlchloroethane
Abbreviation used in this manual : EDC

Odour Like chloroform
Chemical formula CH2Cl.CH2Cl
Boiling point 83.5C
Freezing point -35.3C
Molecular weight 98.97
Specific gravity gas (air = l) 3.42
liquid (water at 4C = 1) 1.257 at 20C
Latent heat of vaporization 85.3 cal/g
Flammability limits in air 6.2 to 15.9% by volume
Solubility in water 0.869 g/100 ml at 20C
Pertinent chemical properties Flash point 12 to 15C. Stable and noncorrosive
Method of evolution as fumigant By evaporation of liquid. Always used in mixture with nonflammable fumigant or carrier, such as carbon tetrachloride

Natural vapour pressure at different temperatures

0C (32F) 23 mm Hg
10C (50F) 40 mm Hg
20C (68F) 65 mm Hg
25C (77F) 81.0 mm Hg
30C (86F) 103.0 mm Hg
40C (104F) 160.0 mm Hg

Weights and volumes of liquid

1 lb (avdp) at 20C has volume 360.8 ml
1 U.S. gal weighs 10.47 lb (4.753 kg)
1 Imp gal weighs 12.57 lb (5.702 kg)
1 kg has volume 795.5 ml
1 litre weighs 1.257 kg

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

By volume

Weight per volume

Parts per million Percent g/m lb/l 000 ft
50 0.005 0.20  
200 0.02 0.81  
247 0.025 1.00  
500 0.05 2.02 0.13
1 000 0.10 4.05 0.25
3 953 0.395 16.00 1.00
20 000 2.0 80.95 5.06

1Ounces per 1000 cubic feet or milligrammes per litre

Wheat treated at 1 l/m (9 gallons/1 000 bushels) with 3 : 1 ethylene dichloride/carbon tetrachloride mixture, triple the dose recommended by the United States Department of Agriculture, showed a maximum of 140 mg/kg ethylene dichloride three days after application of the fumigant. Loss of fumigant during tempering and cleaning processes was up to 70 percent and the maximum residue found in the flour made from this batch was 5 mg/kg. Other investigations have shown similar results, with a gradual reduction in the residue level over a number of weeks; the level of EDC in bread made from white flour of treated wheat was generally below 0.05 mg/kg (FAD/WHO, 1980). Similar desorption has been shown to take place when flour is fumigated with EDC and baking tests carried out after seven days of airing, have shown no detectable reduction in baking quality and no taint of the fumigant in the finished bread.

When added to grain fed to cows, at levels up to 1 000 mg/kg an average of less than 0.25 mg/kg ethylene dichloride was found in the milk. There appears to be no direct correlation between amounts of ethylene dichloride added to the grain and that found in the milk (Sykes and Klein, 1957). In a two-year test on laying hens with EDC at 250 and 500 mg/kg in the diet Alumot et al, (1976) reported a decrease in egg weight from month four and egg production was affected at 500 mg/kg.

The guideline tolerances for residues of EDC recommended by FAO (FAD/WHO, 1980) are 50 mg/kg for cereal grains, 10 mg/kg for cereal products intended for cooking and 0.1 mg/kg for bread and other cooked cereal products.

METHODS OF ANALYSIS

Residual EDC in stored products can be determined by gas chromatography, following cold extraction with acetone-water solvent (Heuser and Scudamore, 1969b) or after continuous solvent co-distillation from a suspension using toluene and boiling water (Bielorai and Alumot, 1966). Page and Kennedy (1975) used vacuum distillation and gas chromatography for determination of residues in spice oleoresins. A method for analysing residues in biological samples was given by Zuccato et al, (1980).

Winteringham (1942, 1944) described a method for recovering EDC from foodstuffs with analysis by the Volhard titration.

APPLICATION

The EDC/CT mixture is a liquid at ordinary temperatures, and its application for grain fumigation is described in Chapter 10.

If it is used in a fumigation chamber, as for instance with bagged seed, the liquid may be poured into a shallow pan or directly onto the bags. Vigorous circulation with a fan or blower is needed during the first hour of treatment for complete volatilization of the liquid and even distribution of the gas, which is much heavier than air.

PRECAUTIONS

Ethylene dichloride has a strong, sickly, chloroform-like odour, detectable at about 50 ppm in air, which gives ample warning of unsafe concentrations (Rowe, 1957). The dosage of EDC/CT mixture usually recommended for space fumigation is between 224 and 288 g/m (14 to 18 lb/l 000 ft). This is above 2 percent by volume in air of the mixture of the two gases. Therefore, a standard industrial-type respirator will not protect against a full fumigation concentration. However, because the mixture is applied as a liquid, a respirator is useful before the full concentration is reached. One should be worn when the fumigant is being poured during application in a chamber to the surface of bulk grain or to the grain stream. A respirator with a fresh canister may also be worn when the space is entered after fumigation following a period of preliminary aeration. The odour of the two ingredients of the mixture should indicate whether or not protection is being given by the canister.


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