MEBROM - Methyl Bromide
Methyl Bromide is a colourless, odourless gas that is mainly produced by nature (oceans, rice fields, etc.). As nature also absorbs Methyl Bromide, there is a constant natural cycle of the gas.
A very small part of all methyl bromide is made by humans. It is generally acknowledged as the 'gold standard' of persticides for agricultural use (plant protection agents) and for desinfestations of containers, silo's, mills, grain carriers, ... It is stored as a liquid under pressure in cylinders; but because of its low boiling point (3.6 °C) it turns into a gas when it is released from the cylinder.
It is non-flammable, spreads fast, penetrates quickly and is very effective (full effect 24h. after gassing). It destroys fungi, nematodes, weeds and insects in any stage of life (egg, larva, pupa, adult).
Obviously by definition it concerns a toxic product, which however has been on the market since 1932 and is exclusively used by professionals who, as a result of years of experience, are very familiar with it and who know perfectly well how to handle it. Because of its relative ease of handling and continuous support from manufacturers and distributors, standard procedures and strict safety measures are complied with. A a consequence, accidents are rare.
i. Soil fumigant: mechanised injection or manual surface treatment
Fumigating soil before planting high value crops such as tomatoes, peppers, melons, strawberries, flowers and tobacco. Soil fumigation is carried out prior to planting where crop productivity may be compromised by soilborne pests such as plant pathogenic fungi, nematodes, soil insects or weeds.
Depending on the type of application and the local soil, between 35%-60% of the Methyl Bromide is emitted to the atmosphere at the end of the fumigation when the sheets are removed, often 24 to 72 hours later, as is the case with strawberry production. In the case of row (bed) fumigation, as is the case with tomato production, the traps are left on for the entire growing season, some 60 to 120 days.
Methyl Bromide gas, approximately 40-120 grammes per m², is injected into the soil at a depth of around 20-25 centimeter before a crop is planted. This will effectively sterilize the soil, killing the vast majority of soil pests. Immediately after the Methyl Bromide is injected, the soil is covered with plastic sheets glued together, which slow the movement of Methyl Bromide from the soil to the atmosphere. Another system of mechanised injection is ‘deep injection’ (depth around 80 cm, without plastic sheet covering).
For surface applications or the so-called ‘Hot gas method’
The area to be treated is covered with plastic sheeting and the liquid Methyl Bromide from cylinders is heated up in a heat exchanger, and as gas released into the space between the soil surface and the sheets. Worldwide, except for the USA, this is the principal method of application.
ii. In commodities:
Fumigating of commodities which may be infested with pests when harvested or later. The use of Methyl Bromide in this context is often necessary to meet quarantine and phytosanitary or other contractual requirements for import and export.
Methyl Bromide can be used to fumigate:
Durable commodities like grains, coffee and cacao beans, oil seeds, dried fruit, herbs, nuts, timber, cottonseed, wooden items.
Perishable commodities like fruit, vegetables, flowers. Food safety and health regulations are often requiring these fumigations.
Methyl Bromide gas is released as a vapourised gas or directly from its container into a fumigation chamber or under a tarp containing the commodities. Some commodities are treated multiple times during both storage and shipment.
Methyl Bromide is typically applied directly from the cylinder through a narrow bore application line culminating in an atomising jet to enhance the speed of vaporisation the fumigant.
Commodities may be treated with Methyl Bromide as part of a quarantine or phytosanitary requirement of an importing country.
The amount of Methyl Bromide introduced is calculated according to label, contractual and legislative requirements.
The degree of containment of Methyl Bromide achieved during fumigation can vary widely. Some commodities are fumigated in gastight, purpose build fumigation chambers while others are treated in very poorly sealed bagged stacks.
iii. In structures and transport:
Methyl Bromide is used to safeguard buildings, such as grain storage facilities, flour mills, food processing units, or vehicles, such as ships, freight containers, trucks or trains carrying agricultural commodities from all kinds of pests.
Also here the degree of containment of Methyl Bromide can vary widely. E.g. Some aircraft and modern buildings can be very gastight whereas older structures can at best be only partially sealed.