Alternatives to Methyl Bromide; Integrated Pest Management in Danish Flour Mills 3. Direct alternatives to Methyl Bromide3.1 Carbonyl sulphide (COS) IPM - no patent solution In the case of an acute infestation in a food plant, it is necessary to have a contingency plan. In this project we have looked at several possibilities and below we describe the most obvious alternatives to methyl bromide. In annex 5 there is a schematic survey of these alternatives with a brief description of other local treatments. With the present intensive research to find alternatives to methyl bromide, other solutions are likely to be found in the near future. As mentioned earlier IPM is a flexible system - there is no one single patented alternative for the elimination of pests. The solution or solutions must be tailored to the problem. 3.1 Carbonyl sulphide (COS)COS has been examined as a possible alternative to methyl bromide. The focus so far has been on COS as an alternative to MB against pests in grain in stores and silos. At present there is no commercial source. "Either-or" poison COS is a colourless liquid with its boiling-point at 50,2°C. COS is well known because of its natural part in the sulphuric cycle. COS is a part of the natural sulphur in soil and moorland areas. It is formed by anaerobic decomposition of organic sulphur material. Ventilation COS is like hydrogen cyanide an "either-or" poison, meaning that after a COS poisoning there will be a 100% recovery except for mortal cases. COS is inflammable, but when used to fumigate the concentrations are far under the
explosion limits. COS is very effective against insects and mites in grain. 25 mg/l for 24 hours is enough to kill most insects in all stages, but the rice weevil (Sitophilus oryzae) will require a larger dose or a longer operation time. COS has excellent penetration ability through flour and other closely packed products. No approval in Denmark COS is neither tested nor approved in Denmark for fumigation. If one were to use COS at the present time one disadvantage would be that the gas detecting equipment, used to measure COS-concentrations is not as sensitive as the equipment used to measure Phosphine or Methyl bromide. 3.2 Hydrogen cyanide (HCN)"Either-or" poison HCN has previously been used to fumigate mills in Denmark. It is a colourless liquid and smells of bitter almonds. It is lighter than air and has its boiling-point at 26°C. Characteristics Like COS, it is an "either-or" poison. HCN is inflammable, but when used to fumigate the concentrations are far under the explosion limits. No approval in Denmark HCN is very toxic and extremely quick-acting on most living creatures. It does not have the quick effective penetration that MB has and it is easily dissolved in water. This is very important when used as a fumigant, as it will bind with moisture and can be difficult to ventilate. HCN will have to be approved in Denmark before it can be used again as a fumigant. 3.3 Chloropicrin (CCl3NO2)Characteristics CCl3NO2 has been used as fumigant but is now mostly used as a warning agent in MB fumigation. It was also used as a poison gas during World War 1. It is 5,7 times heavier than air and is non-flammable. CCl3NO2 has its boiling-point at 112,4°C. CCl3NO2 is heavy and very difficult to use. It is very toxic and quick-acting on insects. Ventilation CCl3NO2 is difficult to ventilate and even small amounts in fumigated goods can irritate the eyes for a long time, because of the tear causing effect. No approval in Denmark CCl3NO2 is not approved as a fumigant in Denmark. 3.4 Phosphine (PH3)Approval in Denmark PH3 is used in the form of pellets, tablets or plates. It is slightly heavier than air, specific gravity 1,21/1,0 - boiling-point at -87°C, in impure form it has a carbide or garlic like odour, but when pure this odour is removed. PH3 is explosive at concentrations of more than 1,8% in air. Corrosion risk By oxidation, phosphoric acid is formed, and there is a risk that combined with sufficient moisture, the fumigant can corrode copper, silver, gold and their alloys and thereby make electronic instruments and systems fail. Potentially, problems can arise when using both magnesium and aluminium phosphine. The corrosion risks involved with phosphine have been tested by FORCE Instituttet, København and published in their report. There are precautions that can be taken to avoid corrosion by phosphine in mills. Length of treatment The gas is generated slowly and requires a longer operating time than Methyl bromide. Difficulties can arise when deactivating the powdery residues of tablets and pellets especially when large quantities are used over a short operating time. Good permeation PH3 has good permeation abilities. It operates slowly but very effectively at low concentrations if the operating time is long enough. The operating time is typically 4 days or more depending on the temperature and target insect species. At temperatures under 10°C PH3 should only be used against a selected insect species, exposure times can be more than 14 days in some cases, particularly against Sitophilus spp (grain weevils). Liquid Phosphine Liquid Phosphine Phosphine 2% - carbon dioxide 98%. Unlike the formulation we know today - solid form e.g. pellets/ plates the new form of
phosphine is a 2% liquid formulation with an admixture of carbon dioxide. Phosphine generators Mill fumigation with phosphine has been demonstrated using phosphine supplied from a generator outside the structure. 3.5 Heat treatmentNon-chemical pest control Heat treatment against insects is probably one of the most effective non-chemical methods of pest control. It is not a new method of controlling pests and has in the past been used with reasonable results, in mills and other places where foodstuff pests appear. 24 hours at 50-55°C is used in many US mills. Several countries are at present working on improving heat treatment an lowering costs in order to make it a viable alternative to Methyl bromide. The treatment time is dependent on the temperature generated. Less than one minute at 65°C is mortal for all insects. At lower temperatures more time is necessary. An allowance needs to be made for time taken to heat through solid goods and constructions, to reach insecticidal temperatures. Heat treatment has been used for many years often with excellent results. Heat treatment is not a new pest control method but has in the past been used, sometimes not very efficiently, in mills and other places where foodstuff pests appear. Individual infested areas and pieces of machinery may be treatable by spot fumigation after removing product residues. Ethylene dichloride is still in use for this in some countries and some other materials are under development. 3.6 Carbon dioxide (CO2), phosphine (PH3) and heat.CO2 has been used for many years as a fumigant, but is impractical as a whole mill fumigant. The main disadvantage is that it operates very slowly. By combining CO2 (4-6%) with heat (32-37°C) and PH3 (low dose 65-100 ppm) tests have shown promising results. The method is said to give good insect pest control over a three day exposure or less. 3.7 Sulfuryl fluoride (SO2F2)SO2F2 has its boiling-point at -55,5°C. SO2F2 is odourless, non- flammable and does not cause unwanted taint. Because of its physical characteristics SO2F2 permeates materials quickly and is completely removed by ventilation. SO2F2 was developed under the name "Vikane" in the 1950’s for treatment of houses, churches and other buildings against wood destroying insects. Laboratory tests In the later years there has been research into the possibility of using SO2F2 as a fumigant in food plants. Laboratory tests are still going on concerning dosage, temperature, exposure time, side effects etc. The product is not approved for fumigation of pests in stored product goods, but has the potential as a whole site treatment of premises from which foodstuffs have been completely removed.
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