Commonly Used Fumigants in Food Storages

Many different chemicals in the name of insecticides and pesticides are used to protect our food from insects and pests in go-downs, in food industries and store house before they reach to us. Also not all the chemicals are appropriate for all kind of food commodities. Thus it is important to know the nature of chemicals used, and its toxicity. Below are the list of chemicals that are commonly used as fumigants as mentioned in FAO manual of fumigation.

Fig: Fumigation in go-downs (https://idealpestcontrol.ae/wp-content/uploads/2017/04/fumigation-.jpg)

Phosphine

Phosphine or hydrogen phosphide (PH3) is a low molecular weight, low boiling point compound that diffuses rapidly and penetrates deeply into materials, such as large bulks of grain or tightly packed materials. The gas is produced from formulations of metallic phosphides (usually aluminum or magnesium phosphide) that contain additional materials for regulating release of the gas. Aluminum phosphide is formulated as tablets, pellets or small sachets of powder with additional materials such as ammonium carbamate, ammonium bicarbonate, urea and paraffin to regulate release of fumigant and suppress flammability.

Toxicity: Phosphine is very toxic to all forms of animal life, hence exposure of human beings even to small amounts should be avoided. Poisoning can result from ingestion or inhalation; however, the gas is not absorbed through the skin. A concentration of 2.8 mg/l (ca 2 000 ppm in air) is lethal to humans in a very short time.

Properties of phosphine:

Odour Carbide or garlic-like odour
Chemical formula PH3
Boiling point -87.4°C
Freezing point -133.5°C
Lowest explosion point 1.79% by volume in air
Solubility in water 26 cc/100 ml at 17°C (very slightly soluble)
Method of evolution as fumigant From preparations of aluminium and magnesium phosphide
Pertinent chemical properties Reacts with copper and precious metals.

Methyl bromide

Methyl bromide 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 is an effective and versatile fumigant. The most important of these is its ability to penetrate quickly and deeply into absorptive materials at normal atmospheric pressure. Also, at the end of a treatment, the vapors 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 absorbed by many materials, it may be used for low temperature treatments that are not practicable with many other fumigants.

Toxicity: Methyl bromide is not as toxic to most insect species as are some other commonly used fumigants, such as HCN, acrylonitrile and ethylene dibromide. 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.

Properties of methyl bromide: 

Odor Nil at low concentrations and musty at high concentrations
Chemical formula CH3Br
Boiling point 3.6°C (38.5°F)
Freezing point -93°C
Molecular weight 94.95
Flammability limits in air Nonflammable (see next page)
Solubility in water 1.34 g/100 ml at 25°C
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%

Hydrogen cyanide (HCN)

Hydrogen cyanide was one of the first fumigants to be used extensively under modern conditions. The use of HCN has been declining in recent years, but it is still important in certain fields of application. HCN is very soluble in water. The solution of HCN in water is a dilute acid and this acid render food materials unpalatable and possibly hazardous for human consumption and unappealing for marketing.

Toxicity: HCN is one of the most toxic of insect fumigants. HCN is a powerful, quick acting poison. In humans and other warm-blooded animals it induces asphyxiation by inhibiting the respiratory enzymes and renders tissues unable to absorb oxygen from the blood in the normal manner.

Properties of hydrogen cyanide: Alternative name : hydrocyanic acid; abbreviation used : HCN

Odour Suggestive of almonds
Chemical formula HCN
Boiling point 26°C
Freezing point -14°C
Molecular weight 27.03
Flammability limits in air 6 to 41% by volume
Solubility in water Infinite at all temperatures
Pertinent chemical properties Weak acid. Relatively noncorrosive. When stored as a liquid without chemical stabilizer may decompose and explode in the container.
Method of evolution as fumigant Discharge from steel cylinder with aid of compressed air. By evaporation of liquid absorbed in porous material, such as card board discs or diatomaceous earth. By action of moisture in air on calcium cyanide, or of sulphuric acid on sodium cyanide
Commercial purity 96 to 99%

Ethylene dibromide

Although EDB is a fumigant of considerable utility, it has a high boiling point and is absorbed by many materials, into which it does not penetrate well. It is thus more limited in usefulness than some of the more volatile fumigants. It has, however, found extensive use in soil fumigation, a subject outside the scope of this manual.

Toxicity: Ethylene dibromide is more toxic to human beings than methyl bromide. It is a severe skin irritant and can be absorbed through the skin as well as the respiratory tract.

Properties of Ethylene dibromide
Alternative names: 1, 2-dibromoethane, ethylene bromide
Abbreviation used: EDB

Odor Like chloroform
Chemical formula CH2Br.CH2Br
Boiling point 131.6°C
Freezing point 10 C
Molecular weight 187.88
Flammability limits in air Nonflammable
Solubility in water 0.431 g/100 ml at 30°C
Pertinent chemical properties Stable
Method of evolution as fumigant By evaporation of liquid, often in mixture with other fumigants

Ethylene oxide

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. 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.

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 diarrhea.

 Properties of ethylene oxide:
Alternative names: 1, 2-epoxyethane, oxirane
Abbreviation used in this manual : ETO

Odor Irritating, mustard-like. May be hard to detect in low concentrations
Chemical formula (CH2)2O
Boiling point 10.7°C
Freezing point -111.3°C
Molecular weight 44.05
Flammability limits in air 3 to 80% by volume
Solubility in water Infinite at 0°C
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%

 

Carbon disulphide

Carbon disulphide (CS2) was one of the first fumigants employed on a large scale. Its tendency to burn or explode presents a hazard. Carbon disulphide penetrates well and is still the only fumigant used in certain parts of the world.

 

TOXICITY

Judged on the basis of lethal dosages, CS2 ranks rather low among the insect fumigants because relatively large dosages by weight are required. Carbon disulphide is toxic to humans.

PROPERTIES OF CARBON DISOLPHIDE
Alternative name : carbon bisulphide
Abbreviation used in this manual: CS2

Odor Sweetish when pure; impurities, such as hydrogen sulphide, give characteristic unpleasant odors
Chemical formula CS2
Boiling point 46.3°C
Freezing point -111 C
Molecular weight 76.13
Flammability limits in air 1.25 to 44% by volume
Solubility in water 0.22 g/100 ml at 22°C
Pertinent chemical properties Flash point about 20°C and ignites spontaneously about 100°C
Method of evolution as fumigant By evaporation of liquid; now used more often in nonflammable mixtures
Commercial purity 99.99%

Sulphuryl fluoride

Sulphuryl fluoride has been developed as an effective fumigant for controlling dry wood termites. This gas has outstanding dispersion and penetrating qualities which permit it to infiltrate termite tunnels and crevices and destroy the insects.

Toxicity: Its mammalian toxicity by inhalation, is about equal to that of methyl bromide.

Properties of sulphuryl fluoride 

Odour None
Chemical formula SO2F2
Boiling point -55.2°C
Melting point -120°C
Molecular weight 102.06
Specific gravity
gas (air = 1) 2.88
liquid (water at 4°C = 1) 1.342 at 4°C
Latent heat of vaporization 79.5 BTU/lb at -55.2°C
Flammability limits in air Nonflammable
Solubility in water 0.075 g/100 g at 25°C
Pertinent chemical properties Noncorrosive, relatively unreactive and harmless to wide variety of household materials
Method of evolution as fumigant From steel cylinders under natural pressure
Commercial purity 99%

Chloropicrin

Chloropicrin is a powerful tear gas; it is one of the most toxic to insects of the fumigants commonly used today. It is sometimes added in small proportions to other fumigants, e.g., hydrogen cyanide and methyl bromide, to serve as a warning agent. Although the tear gas effect of Chloropicrin is helpful in preventing persons from staying in dangerous concentrations during the fumigation process, it is also a handicap because fumigated commodities are unpleasant to handle for some time after fumigation. Chloropicrin is corrosive to metals and care should be taken to protect metal surfaces and equipment during treatment.

T0xicity: Chloropicrin is toxic to nematodes and certain fungi and it has found wide application as a soil fumigant. In humans, a concentration of 2.4 g/m³ can cause death. Concentration ss low as 1 ppm of Chloropicrin in air produces an intense smarting pain in the eyes, and the immediate reaction of any person is to leave the vicinity in haste.

Properties of chloropicrin :
Alternative names: trichloronitromethane, nitrochloroform
Strongly irritating tear gas

Chemical formula CCl3 NO2
Boiling point 112°C
Freezing point -64°C
Molecular weight 164.39
Specific gravity
gas (air = 1) 5.676
liquid (water at 4°C = 1) 1.651 at 20°C
Flammability limits in air Nonflammable
Solubility in water 0.227 g/100 ml at 0°C
Pertinent chemical properties Nonflammable; relatively inert; corrosive in presence of moisture
Method of evolution as fumigant By evaporation of liquid from pure compound or mixed with carbon tetrachloride. Sometimes dispersed as aerosol with methyl chloride as carrier.
Commercial purity 99%

Fumigant mixtures

Fumigants are sometimes marketed in mixtures with other compounds. There are a number of practical reasons for combining fumigants. The most important is to reduce risk of flammability and provide different patterns of diffusion.

Reference: FAO manual on fumigation