Fumigants are gaseous forms of chemicals and are very useful in phytosanitary treatments. The imported or exported materials are subjected to fumigation to eliminate the pest risk. The Insect pests or other pests found living on/in the produce, also hide in protected areas in storage premises, food processing units, equipments, etc. None of the insecticidal formulation which may be sprayed in such places, will be effective in containing the pests. It is only the fumigant which could penetrate such inaccessible spots and eradicate pests. Fumigant is a chemical which can exist in gaseous state in/at a required temperature and pressure and is lethal to organisms (insects, animals, plants and other pests) if they are exposed to a sufficient concentration and for a sufficient length of time. There are many chemical compounds which are volatile at ordinary temperatures and sufficiently toxic to fall within the definition of fumigants. In actual practice, however, most gases have been eliminated owing to unfavorable properties, the most important being chemical instability and destructive effects on commodities. An ideal fumigant should have the following characteristics:
- easily & readily produces a high toxic concentration;
- good penetration power;
- safe to handle;
- low toxicity to humans & animals;
- compatibility with commodity;
- low boiling point;
- insoluble in water;
- low sorption rate;
- easily dispersed (diffusion) and aerated;
- leaves no toxic residues in the treated material;
- should not cause damage or detiorate the treated commodity;
- should not corrode metals;
- should not leave any foul smell after aeration;
- flavour in fruits, vegetables, etc. should not be lost.
There is no fumigant which could satisfy all the above characters. However, a fumigant which satisfies most of the conditions is Methyl bromide.
Some of the fumigants in use in different countries are:
- Carbon dioxide (CO2)
- Carbonyl sulphide (CS)
- Carbon tetrachloride (CT)
- Dichlorvos (DDVP)
- Ethylene dibromide (EDB)
- Ethylene Oxide (ETO)
- Formaldehyde (Formalin)
- Hydrogen cyanide (HCN)
- Methyl bromide (MB)
- Phosphine (PH)
- Sulphuryl fluoride (SF)
However, in India, Methyl bromide and phosphine are the most used amongst the registered fumigants. Use of EDB and HCN have been banned in India and ETO & SF are yet to be registered in India for the purpose.
Fumigation cannot be carried out unless: (i) the enclosure can be sealed to an adequate standard (ii) workers and other persons can be excluded from the enclosure and (iii) fumigant can be safely aired from the enclosure after the exposure period is complete. Adequate care is required to be taken while handling and use by the Operators. Moreover, Operators are required to have knowledge of fumigants registered in our country and situation under which they could be judiciously used. This would also help in overcoming the problem of pesticide residue in treated commodities. Most used fumigants are Methyl bromide, Phosphine, Sulphuryl fluoride, Ethylene oxide, Carbon dioxide, etc. Presently, in India, only three fumigants, namely, Methyl bromide, Aluminium phosphide and Magnesium phosphide are registered for use under the Insecticides Act, 1968. Their use has been restricted due to their hazardous nature or otherwise.
Fumigation Process in brief
Fumigation generally involves the following phases: First the commodity intended to be fumigated is usually covered to create a sealed environment; next the fumigant is released into it; then this space is held for a set period while the fumigant gas percolates into all over the space and acts on and kills any infestation in the product. Next the space is ventilated so that the poisonous gases are allowed to escape from this enclosure, and render it safe for humans to enter. If successful, the fumigated area is now safe and pest free.
Drawback: Since there is no gas or residue left in the fumigated Cargo, it may get re-infested either through cross-infestation or otherwise on finding a favourable environment, as the time lapses.