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.
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|
|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 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|
|Boiling point||3.6°C (38.5°F)|
|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|
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|
|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%|
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
|Freezing point||10 C|
|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|
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|
|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.|
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.
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|
|Freezing point||-111 C|
|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|
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
|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|
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|
|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.|
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
Name : Pratiksha Shrestha
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.