Fumigants for insects control
- Monday, October 30, 2017
- by
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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
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 aluminium or magnesium phosphide) that contain additional materials
for regulating release of the gas. Aluminium 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
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.
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 hydrogen cyanide
Odour
|
Nil at low concentrations;
strong musty or sickly sweet 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 sorbed 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 in this manual : EDB
Alternative names : 1, 2-dibromoethane, ethylene bromide
Abbreviation used in this manual : EDB
Odour
|
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 diarrhoea.
properties of ethylene oxide
Alternative names: 1, 2-epcxyethane, oxlrane
Abbreviation used in this manual : ETO
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
|
10.7°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 disulphide
Alternative name : carbon bisulphide
Abbreviation used in this manual: CS2
Abbreviation used in this manual: CS2
Odour
|
Sweetish when
pure; impurities, such as hydrogen sulphide, give characteristic unpleasant
odours
|
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.
Toxicity
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
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 tetrachltride.
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 more important being. The most important is to reduce risk of flammability
and provide different patterns of diffusion.Source: http://www.fao.org/docrep/X5042E/x5042E08.htm#Methyl bromide
