Types of Fumigants
1. Methyl Bromide (Bromomethane)
Methyl Bromide, at normal temperature, is a colourless gas 3.27 times heavier than air. The pure gas has a faintly sweet smell but it normally has a marker added for warning which causes watering of the eyes.
There is widespread international concern over Methyl Bromide because of its properties as a category one ozone depletant under the Montreal Protocol of 1992. Not withstanding its abilities as a fumigant there is a mounting consensus that a more suitable substance must be found by the end of the century. Methyl Bromide is highly toxic to mammals and is the most widely used fumigant for timber, agricultural products, empty containers, foodstuffs, seeds and plants. In particular Australian quarantine clearance by AQIS requires this method which includes fumigation against :
- Weeds and organisms within soil and compost,
- Insects and mites,
- Infestation in fresh fruit,
- Within nursery stocks of plants.
Effect on foodstuffs: After fumigation the bulk of methyl bromide is removed by aeration although there may be small residues. There can on occasion be a chemical reaction with certain food products if some absorption takes place.
Methyl Bromide is absorbed by oils, fats and finely ground materials. It can also react with materials containing sulphur to cause discoloration or odour. The following materials are among those which should not normally be fumigated by Methyl Bromide.
- Butter, lard, fats, avocado, soybean flour, flours and baking powders,
- Bone meal, charcoal and cinder blocks,
- Furs, felts, horsehair, pillows, rugs and papers,
- Iodised salt,
- Leather goods and photographic chemicals (excluding film).
- Photographic prints,
- Rubber goods,
- Woollen goods
Health Warning : Exposure to Methyl Bromide has in the past resulted in a number of deaths. A particular danger is that signs of poisoning may be delayed for several hours following exposure to the gas. There is no significant antidote and the human body can absorb it by inhalation and via the skin.
Headache, dizziness, eye irritation, coughing, nausea, abdominal pains and numbness of the feet are early indications of poisoning.
Methyl Bromide is usually administered from approved cylinders or cans. It is important to stress the use of the correct protective clothing during fumigation.
Guideline quantities : For ANZ destinations - 5.0 lbs per 1000 cft or 80 gms/cbm For USA destinations - 4.5 lbs per 1000 cft or 72 gms/cbm For other destinations- 3.0 lbs per 1000 cft or 48 gms/cbm
Phosphine used for fumigation purposes is usually produced by the reaction of atmospheric moisture with slow release formulations containing aluminium or magnesium phosphide.
Phosphine is highly toxic although it requires a relatively high temperature and long exposure period to be effective. Under normal conditions Phosphine is a gas and is colourless and odourless. A fishy or garlic-like smell may be evident due to impurities.
A significant fire/explosion risk associated with phosphine is reduced by using metal phosphides specially prepared for fumigation purposes. Care must be taken during use to isolate any electrical connection (switches can be covered in paraffin wax) and any sources of ignition must be removed.
Phosphine is used for fumigating a wide band of insects and pests. It has a low degree of absorption by foodstuffs and penetrates well into the stored product.
Australian AQIS recognise its advantages over Methyl Bromide on milled and oily commodities such as flour, soybean flour, fishmeal, nuts and oilseeds. It is however not favoured for use on timber due to concerns over its ability to penetrate the material.
Health Warning : Very poisonous and very similar symptoms to those of Methyl Bromide if exposed to it. A notable effect is chest tightness and difficulty in breathing.
Phosphine preparations for fumigation are dispensed as :
- Powder sachets
- Degesch plates impregnated with metal phosphide formulations and sealed prior to use
- Bag blankets or beltsMixed in cylinders with CO2 with 3% phosphine.
- Tablets or pellets,
Guidelines on tablets : 3 tablets per CBM. The advised temperature for Phosphine NOT to be used below 10 deg C.
3. Sulphuryl Fluoride
Sulphuryl Fluoride (Vikane) is used extensively in the USA to control insect pests in timber. It should not be used on living plants and foodstuffs. It does have an advantage over Methyl Bromide in that it does not have any harmful effects on photographic supplies, metals, electronic components, paper, leather, rubbers, plastics and wallpapers.
4. Ethylene Oxide
Approval for use in foodstuffs was withdrawn by Australian authorities (AQIS) in 1988 due to concern over toxicity of residues formed in some foods. The properties of Ethylene Oxide as an insecticide and effectiveness in devitalising seeds make it specific to special needs such as fumigating rice straw matting.
A major drawback is the explosive qualities of Ethylene Oxide requiring it to be normally applied under vacuum.ç
5. Ethylene Dibromide (EDB)
Used for years as a treatment for fruit fly in fresh fruit and vegetables and agricultural needs this form of fumigation has gradually been replaced.