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Plant products in bags may readily be fumigated with methyl bromide while they are still loaded in ships and barges. If proper provision is made for the even distribution of the fumigant throughout the load any full cargo space may be fumigated. An important consideration is that in large spaces it may take some time to complete thorough aeration after treatment (Monro, 1947b; Markin, 1963). Treatment of bulk grain in cargo ships is discussed in Chapter 10.
Phosphine may also be used For treatments in barges if the longer exposure periods recommended For the use of this Fumigant are practicable. As stated in Chapter 6, due consideration must be paid to the presence of coppercontaining equipment in the structure. A procedure for the use of phosphine in combination with methyl bromide for the fumigation of bulk loaded expeller in barges and coasting vessels has been developed by Wohlgemuth et al (1976).
The methyl bromide cylinders are placed on the open deck and Cannected ted to copper or olyethylene tubing leading into the holds and ending in one or more T-shaped nozzles. At least one 25- or 30-cm (10- or 12-in) circulating fan should be placed as near as possible to the bottom of each hold and, when the gas is released, the fans should be operated for 30 minutes in order to prevent stratification and to aid distribution of the yes. Fans are also useful in hastening aeration after fumigation.
The penetration of methyl bromide is outstanding and the gas will escape unless adequate precautions are taken for sealing. A single ordinary canvas tarpaulin is not sufficient to contain the gas during the fumigation period. However, three canvas tarpaulins in good condition are able to prevent leakage, especially if they are dampened. Suitable sizes of special tarpaulins with a plastic coating impervious to methyl bromide may be obtained to cover the hatches. If suitable or sufficient tarpaulins are not available, strips of tar paper joined together by various widths of brown paper glued with flour paste should be laid down above the hatches, with ordinary canvas tarpaulins then placed on top. Canvas tarpaulins usually provide sufficient cover for the ventilators.
Many modern ships have steel rolling hatch covers, called "McGregor type", which require no extra sealing for methyl bromide fumigation. These covers are lowered into place off their dollies onto a rubber gasket and the full weight is sufficient for a good seal. If the dollies are warped after rough use the side bolts may be used to pull them down into place.
When methyl bromide is used, the ships' officers, with their knowledge of the construction of the vessel, may be of great assistance to ensure that adequate sealing is obtained. They can point out possible sources of leakage, help check the ventilation system and openings between bulkhead on older ships and also see that hatch covers are secured properly (Monro, 1969).
Phosphine may be applied in barges loaded with bagged goods according to the procedures described below in this chapter for wheeled carriers.
If the cargo space of a vessel is fumigated while the ship is in port, it is recommended that the entire crew be evacuated while the fumigation is in progress. Warning notices should be prominently displayed at gangways and entrances to accommodations and a guard should be stationed at each gangway to prevent unauthorized persons from going aboard. No one should be allowed to return to quarters until the ship has been certified "gas free" by the fumigator in charge. Further information on the safety procedures recommended for fumigation of ships in port can be obtained from the Inter-governmental Marine Consultative Organization, MSC Circular 298, 23 January 1981 (IMCO, 1981) or to subsequent documents as they are updated.
On board ship there may be rooms usable as fumigation chambers. Ammunition and other storage lockers are usually gas-tight and of sufficient size for treating small amounts of infested goods. Fumigation is conducted in the same way as in a regular chamber. Extra care must be taken during aeration because, in the absence of a proper exhaust vent, the gas will diffuse out through doors and portholes.
Empty holds in cargo ships or on some passenger vessels often have residual populations of stored-product insects. If the infestation is localized, it can be controlled by spraying with a suitable insecticide. This method, however, cannot be relied upon for complete eradication. Usually, a complete fumigation is required (Monro, 1969).
Aerosols, which are fogs, mists or insecticidal smokes produced by various devices, have already been mentioned in the Introduction. They can be used to treat populations of stored-product insects in empty holds, and are satisfactory for killing the insects exposed in the open. Some information on the use of dichlorvos for control of insects in empty cargo ships is given by Bond et al (1972). However, all of these materials, including dichlorvos, have poor powers of penetration and are not as efficient as fumigants for obtaining complete control throughout the structure.
When a fumigant is used, one or two boards covering the bilges in each side of the ship should be removed. Piles of dunnage, if present, should be broken up to allow penetration of the gas from every side.
Methyl bromide penetrates well into cracks, crevices and spaces under boards. In such places there are accumulations of grain and other foods in which the insect populations are able to multiply and from which they spread to the cargoes and other parts of the ship.
The fumigation of empty holds with methyl bromide follows the same basic procedure already described for loaded cargo spaces. Fans placed at the bottom of the holds are again absolutely necessary to give proper gas distribution. Recommended treatments are given in Schedule Q. It will be noted that dosages are lower and exposure periods shorter than those for loaded spaces.
To eradicate Irogoderma beetle infestations, more particularly Irogoderma qranarium Everts, increased dosages of methyl bromide are needed (Slabodnik, 1962; see Schedule Q).
HCN may also be used in empty holds although it does not diffuse very well through residual debris from plant products to reach deep-seated infestations. The most convenient method to apply HCN in ships is by means of the impregnated discs. These are often kept on hand for medical quarantine fumigation against rats.
With HCN, the general preparations and precautions are the same as for methyl bromide, with the following points of difference.
1. The ordinary canvas hatch tarpaulins, if in good condition, are satisfactory for HCN fumigation; it is advisable to use two to each hatch.
2. If fans are used for distribution of HCN within the hold, they must be explosion proof.
3. The discs are distributed as widely as possible in the hold by lifting the tarpaulins on each corner of the hatch in turn; this work is facilitated by removing the four corner hatch boards before the fumigation.
4. The tarpaulins are then battened down securely.
Procedure and precautions for the ventilation of empty cargo ships are the same as already described for loaded ships. The gases diffuse more quickly from the empty holds and, under conditions favourable for aeration, the holds may be entered two or three hours after the hatches are opened.
Some wheeled carriers may be used for fumigation. Treatment in such vehicles is often convenient and may show considerable economy in time and labour. By making a treatment of infested goods in a carrier, at least four manipulations, involving loading and unloading the vehicle and the fumigation chamber, are avoided. Furthermore, the fumigation kills the insects in the free space of the carrier and live pests do not remain behind to infest or invade the next load. In this way a great deal of possible cross-infestation may be avoided.
Railway companies are usually willing to permit fumigations in their equipment. It is, of course, essential to solicit their cooperation before treatments are planned.
In some countries, the standard railway cars (wagons) are well built and constitute in themselves excellent fumigation chambers; steel cars are especially suitable. Refrigerator-type cars, by the very nature of their construction, are usually gas tight if all openings are carefully sealed. (It is important to remember that in the cars using ice, drainage pipes from the ice bunkers should be plugged during the fumigation). In all railway cars, the wooden floor is likely to be the principal site of leakage. Some cars that are not sufficiently gas tight may be readily sealed by some of the methods already described. Also, 8 leaky car could be covered with a gas-proof sheet and fumigated, if a satisfactory seal can be made at ground level and around the rails. When railway cars are to be fumigated, they are usually isolated on separate sidings and kept there while under gas. This arrangement is, of course, essential if the cars are covered with sheets. In some countries, under certain circumstances, railway cars may be allowed to travel while still under gas. Appropriate warning signs are placed on the main doors or hatches, with instructions for the adequate airing of the car before it is entered for inspection or unloading.
In France and in the United States, there are special fumigation chambers with railway tracks running into them so that the cars may be fumigated singly or in groups. Some of the chambers are designed for fumigation at atmospheric and others at reduced pressures. This arrangement has the advantage of allowing treatment of both the inside and outside of the vehicles, a consideration which may be important from the quarantine point of view, especially at border points.
The fumigation of railway cars under gas-proof sheets, as described above, may seem to eliminate the need of constructing permanent chambers. In plant quarantine practice, however, the choice of method against the threat of introduced pests should be made on the grounds of efficacy rather than of convenience or economy.
TRUCKS AND CARGO TRAILERS
Highway vehicles that can be rendered gas tight are suitable for the fumigating of goods loaded into them. In general, the same considerations apply as for railway cars.
For certain operations, the use of gas-proof sheets, particularly of the light-weight polyethylene type, is a convenient and effective improvisation. In this work, the trucks or trailers may be driven onto a gasproof groundsheet and then covered with another sheet, which is sealed to the lower one with snakes in the usual manner, thus providing a gasproof structure around the vehicle.
Fumigation of many commodities is carried out in freight containers and other transport units that are designed for carriage on vehicles. The procedures for treatment of these containers are much the same as for railway cars and cargo trailers. They may be fumigated while stationary or the treatment may be continued "in transit". Procedures for fumigation of tobacco with phosphine in freight containers, along with efficacy of the treatment, have been outlined by Childs et al (1971).
If the freight containers undergoing fumigation are to be loaded on ships, the guidelines given by the Inter-governmental Maritime Consultative Organization (IMCO, 1981, or subsequent recommendations) should be followed.
FUMIGANTS FUR CARRIER TREATMENTS
In practice, methyl bromide and phosphine are the materials most commmonly used for wheeled carriers containing plant products, because these two yeses penetrate effectively into many commodities. Ethylene dibromide was used successfully in the United States for truck fumigation in the campaign against the Mediterranean fruit fly in Florida. Truckloads of oranges were run into atmospheric chambers equipped with ducts specially designed for cirulating the fumigant/air mixture through the load (Grierson and Hayward, 1959).
APPLICATION OF FUMIGANTS
In general, the techniques of sealing sod fumigant application are the same as those already described for the atmospheric chamber or gas-proof sheet fumigations.
Fumigation of bagged grains, meals and other plant products in carriers, such as railway cars, is easily done with methyl bromide in cans (0.45 or 0.68 kg) or in steel cylinders. This fumigant should always be applied from outside a railway car using 6 mm (0.25 in) polyethylene or copper tubing attached to the cylinder or to the special opener/applicator designed for cans. The tubing is inserted through a crack between the door and door frame, through a roof vent or possibly through a hole drilled in the floor. The discharge end of the tube is plugged sod a hole drilled through both walls 3-4 cm below the tip, then the end of the tube is attached close to the ceiling at the centre of the car, so that the methyl bromide mist can be directed over the commodity and toward both ends of the car.
The dosage to be applied is determined according to the size of boxcar as well as the temperatures of the atmosphere and the commodity. Temperatures above 10°C with exposure periods of 12 to 18 hours are recommended for this treatment. After applying the proper dosage the tubing is withdrawn and the opening sealed. At the end of the fumigation period all doors and vents are opened to allow as much circulation as possible. At least 30 to 60 minutes are required to aerate the free space of the car, but appropriate detecting equipment should be used to make sure that no methyl bromide is present when personnel enter to unload the car. Respiratory protective equipment should be worn when checking for fumigant in the car.
Various formulations for generating phosphine are used in fumigating railway cars and other carriers. Tablets or pellets of aluminium phosphide may be used by placing them in moisture-permeable envelopes and attaching these at intervals to the wall of the carrier or placing them in shallow cardboard boxes on top of the load (Schoenherr et al, 1966; Schesser, 1967). To avoid the possibility of combustion, only two tablets or ten pellets should be inserted in each envelope. Prepacks, with pellets appropriately separated from one another in a specially prepared plastic strip and covered with permeable paper, are supplied by some manufacturers for convenient application of the fumigant. They ore sometimes attached to the inner side of the door just prior to closing and sealing. If sachets are used they may be strung by a thin rope above the load. Lochner (1964b) gave a full description of the use of aluminium phosphide tablets for the fumigation of maize in bags or in bulk while in transit in railway cars. Magnesium phosphide in tablets, pellets or embedded in moisture-permeable plastic plates is also available for use in a similar way.
The general precautions for railway cars and freight containers are similar to those already recommended for buildings and ships.
If a line of cars is being treated, it is advisable to put the usual gas warning sign on a special stand, which is staked in a conspicuous spot beside or between the railway tracks at each end of the line. Railway sidings chosen for holding cars during fumigation should be at least 100 m from any dwelling or building regularly occupied.
Where in-transit treatments are carried out, warning signs should be placed in conspicuous locations near each door of the carrier. They should be firmly fixed so that they are not easily lost or removed before the car or container is opened for aeration. For such in-transit treatments the warning signs should indicate the date of fumigation as well as the type of fumigant. Prior to unloading of fumigated vehicles, appropriate tests should be made to ascertain safety of the cargo area.
The success of in-transit fumigations is particularly dependent on good construction of the railway car or freight container and effective sealing methods.
Fan circulation is essential in carrier treatments for fresh fruit, vegetables, plants and nursery stock when using a fumigant such as methyl bromide. This is to ensure proper evaporation and distribution of the fumigant in treatments of short duration (2 to 4 hours).
In fumigation of bagged grain and plant products, the exposure periods are at least 12 hours. If the fumigant is evenly distributed above the load at the time of application, subsequent fan circulation is unnecessary.
BULK GRAIN TREATMENTS
Fumigations of bulk grain may be carried out in railway cars and in wellbuilt trucks. The principles and techniques are essentially the same as for bulk grains in flat storages (as described in Chapter 10). Alumirlium phosphide tablets applied by probes or sachets inserted in the bulk may be used. Liquidtype fumigants have also been used in open-top transit trucks with the grain being covered with a gas-proof sheet after application. A canvas tarpaulin can be used as an additional cover (Gray et al, 1964).
Gaseous-type fumigants such as methyl bromide, may also be used if provision is made for adequate recirculation with special equipment (see Phillips and Latta, 1953; USDA, 1963).
Techniques for applying small doses of a fumigant to individual bays, packages or other containers show considerable promise for use either in emergencies or where converitional fumigation equipment is not available. There are at present two factors which may assist the development of such methods for practical use. First, some modern packaging materials are sufficiently gas tight to retain the vapours for the length of time required for successful treatment. Second, there are fumigants which can be applied conveniently to containers and which also have physical properties, such as slow evaporation or diffusion, that are suitable for this purpose.
In India, ethylene dibromide was injected into grain, stored in jute bags, at the rate of 10 ml per bag. This either killed the insects present or drove them out (Pingale and Swaminathan, 1954). Experiments with injection of four other fumigants into insecticide-impregnated jute bags containing grain confirmed the greater efficacy of EDB for this purpose. Control was not complete in non-impreynated bags (Muthu and Pingale, 1955).
The use of small cardboard discs held in aluminium foil, as described in Chapter 6, has been found useful for bag treatments (Muthu, 1964). These discs are illustrated in Figure 36. In Ghana, EDB was successfully used on individual jute bags with polyethylene liners as described in Chapter 6 (Hall, 1°63).
It should be noted that EDB is now considered to be hazardous to human health and, therefore, care should be taken to ensure that no one is exposed to its vapours and treater) grain should be thoroughly aired so that residue is reduced below the FAD guideline levels (FAD/WHO, 1980).
In the United Kingdom, two tablets of aluminium phosphide were inserted individually into bags of wheat and rye resting on gas-proof sheets. One tablet was placed near the middle anti one near the mouth of the hag. Tablets were deposited either by hand or with a special probe dispenser. The gasproof sheets were then wrapped over small groups of bays and well overlapped. After five days of exposure, the sheets were removed. This treatment gave good control of a representative collection of species of stored-product insects and mites, although some adults of the granary weevil, Sitophilus qranarius, survived in cold wheat used in one test. It appears that this method holds promise for treatments of sacked grain in farm storages or other places where little special skill is required. for the control of certain insect species, such as the granary weevil, the dosage per bag should be increased to three tablets (Heseltine and Thompson, 1957).
Using polyethylene-lined sacks, Proctor and Ashman (1972) achieved good control of insects in bags of groundnuts being transported from Zambia to the U.K.. When a 0.6 9 aluminium phosphide pellet was applied in jute or woven polypropylene sacks of 32-82 kg capacity and lined with polyethylene 63.5127.5 µm thick, the c x t product for phosphine exceeded 50 mg h/l, and 10C percent mortality of all stages of the test insects, including Sitophilus zeamais Mots. was recorded. Although many liners in sacks split during transportation, this did not affect the efficiency of the phosphine fumigation or permit reinfestation.
PACKAGING LINE TREATMENTS
Treatments on the packaging line are of concern at present in the food processing industries, and the subject falls more in the realm of industrial rather than agricultural practice. Some discussion of the techniques is given here, not only because they are interesting examples of how fumigants may be used, but also because similar methods might be applied to solve more strictly agricultural problems.
Packaging line treatments have helped to keep certain food products, such as dried fruit and vegetables, free from infestation as they leave the processing plant (Simmons and Fisher, 1946). The technique is applicable when the packages are made of materials, such as cellophane and fibreboard, through which fumigants do not diffuse very quickly. The fumigants are dispensed into the individual packages from automatic machines, which can be calibrated to give an accurate dose. Application may be made before or after the contents are placed in the package. The best stage is just before the package enters the unit which seals the wrapping. The wrappings generally used are sufficiently gas tight to maintain an insecticidal concentration of the fumigant long enough to kill any insect stages present in the package.
To protect plant workers, exhaust hoods, approved by health authorities, should be installed to draw fumes away from the working area (Mayer and Nelson, 1955). Also, appropriate analytical tests should be made to ensure that threshold limit values for the fumigants are not exceeded. Experience has shown that fumigants diffuse away from the packages fairly rapidly after application, sometimes within 48 hours. Thus, it is considered that these treatments do not create any hazard to consumers.
Fumigants used for this type of application include methyl bromide, ethyl acetate, ethyl formate and propylene oxide. In the past, methyl bromide has been mixed with high proportions of carbon tetrachloride for package treatments.
Propylene oxide and ethylene oxide are also applied to certain packaged foods, especially dried fruit, to prevent microbial spoilage and to control insects.
Dosages for packaging line treatments vary greatly according to the product, material used for packing, method of packing and fumigant used.
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