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What is Fumigation? - A technique of pest control using a toxic gas
 

What is Fumigation? - A technique of pest control using a toxic gas

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Whereas conventional insecticides work by the pest species making contact with the dried toxic deposits or of airborne or surface dry particles or liquid droplets, often by way of the cuticle but ...

Whereas conventional insecticides work by the pest species making contact with the dried toxic deposits or of airborne or surface dry particles or liquid droplets, often by way of the cuticle but sometimes by ingestion, fumigants always work in the gaseous form, entering the pest’s body through it’s respiration system - the spiracles in the case of the invertebrates.

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    What is Fumigation? - A technique of pest control using a toxic gas What is Fumigation? - A technique of pest control using a toxic gas Document Transcript

    • Digital Re-print - March | April 2014 What is Fumigation? - A technique of pest control using a toxic gas www.gfmt.co.uk Grain & Feed MillingTechnology is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2014 Perendale Publishers Ltd.All rights reserved.No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872
    • W hereas conventional insecti- cides work by the pest species making contact with the dried toxic deposits or of airborne or surface dry particles or liquid droplets, often by way of the cuticle but sometimes by ingestion, fumigants always work in the gaseous form, entering the pest’s body through it’s respiration system - the spiracles in the case of the invertebrates. True fumigants should be differentiated from insecticidal smokes, fogs and mists, which are often incorrectly referred to as fumigants. Fumigants are gases, which dif- fuse as separate molecules, penetrating into the materials being fumigated. The com- pletion of a fumigation requires aeration or ventilation which removes all traces of the fumigant gases, although other residues may remain, which will be discussed later. Smokes, fogs and mists are air-borne sus- pensions of solid or liquid particles, which will be deposited on the outer surfaces of the materials being treated (foods, packag- ing or structure) without any degree of penetration. For example, it is quite com- mon to hear farm workers talking of fumi- gating their grain stores, as they prepare to apply a canister of a pesticidal smoke. The smoke generator can seem very impressive, but will have almost zero penetration into sacks and bags or into dried food spillage. It is only true fumigants that can kill pests hiding in deep deposits of spillage or of the foodstuffs themselves. We will see this aspect of fumigation again when we discuss treating grain heaps, or silos and bins of grain, or flour or bag stacks in food stores. Fumigant gases kill target pests via the respiration system, usually by preventing the transfer of oxygen into the tissues. Ideally a fumigant will work rapidly, and not leave an harmful residues. But there can be other issues with fumigation. Of the fumigants left in use in the 21st century, some require quite a high working tempera- ture (around > 25°C) to effectively control insect eggs, some need extended exposure periods (often in excess of 2 weeks con- tinuous exposure – grain weevils, and spider beetles, for example, or for the tiny booklice and mites, sometimes even needing two fumigations separated by 10 days! But by far the biggest disadvantage of fumigation is lack of long-term effect. Once it’s gone it’s gone! And, unlike the dried powder or spray deposits of conventional insect control, fumigated goods are open to re-infestation immediately after the gas has dis- persed. It is definitely difficult to use fumigation as a protective (prophylactic) measure, despite the claims of some fumigation companies over the years. All depends on totally protecting the commodity from further attack. In fact the real and unique advantage of fumigation is its penetration through bulks and all woven bags of dried commodity Fumigation - its practice and effectiveness Because all fumigants are at least as toxic to all animals, including humans, as to invertebrates, in Europe and the USA, fumigation of commodities and buildings can only be carried out by trained and certificated fumigation operators. However, it is very useful for all involved in the storage of food commodities and working in food manufacturing plants, to understand the prin- ciples and practical aspects, and constraints, What is Fumigation? A technique of pest control using a toxic gas by Mike Kelly, Acheta What is Fumigation? 1. A technique of pest control using a toxic gas. Whereas conventional insecticides work by the pest species making contact with the dried toxic deposits or of airborne or surface dry particles or liquid droplets, often by way of the cuticle but sometimes by ingestion, fumigants always work in the gaseous form, entering the pest’s body through it’s respiration system - the spiracles in the case of the invertebrates. True fumigants should be differentiated from insecticidal smokes, fogs and mists, which are often incorrectly referred to as fumigants. Fumigants are gases, which diffuse as separate molecules, penetrating into the materials being fumigated. The completion of a fumigation requires aeration or ventilation which removes all traces of the fumigant gases, although other residues may remain, which will be discussed later. Smokes, fogs and mists are air-borne suspensions of solid or liquid particles, which will be deposited on the outer surfaces of the materials being treated (foods, packaging or structure) without any degree of penetration. For example, it is quite common to hear farm workers talking of fumigating their grain stores, as they prepare to apply a canister of a pesticidal smoke. As seen below, the smoke generator can seem very impressive, but will have almost zero penetration into sacks and bags or into dried food spillage. So it is only true fumigants that can kill pests hiding in deep deposits of spillage or of the foodstuffs themselves. We will see this aspect of fumigation again when we discuss treating grain heaps, or silos and bins of grain, or flour or bag stacks in food stores. Fumigant gases kill target pests via the respiration system, usually by preventing the transfer of oxygen into the tissues. Ideally a fumigant will work rapidly, and not leave an harmful residues. But there can be other issues with fumigation. Of the fumigants left in use in the 21 st century, some require quite a high working temperature (around > 25°C) to effectively control insect eggs, some need extended exposure periods (often in excess of 2 weeks continuous exposure – grain weevils, and spider beetles, for example, or for the tiny booklice and mites, sometimes even needing two fumigations separated by 10 days! But by far the biggest disadvantage of fumigation it is lack of long-term effect. Once it’s gone it’s gone! And, unlike the dried powder or spray deposits of conventional insect control, fumigated goods are open to re-infestation immediately after the gas has dispersed. It is definitely difficult to use fumigation as a protective (prophylactic) measure, despite the claims of some fumigation companies over the years. All depends on totally protecting the commodity from further attack (see later in article) In fact the real and unique advantage of fumigation is its penetration through bulks and all woven bags of dried commodity 2. Fumigation - its practice and effectiveness Because all fumigants are at least as toxic to all animals, including humans, as to invertebrates, in Europe, fumigation of commodities and buildings can only be carried out by trained and certificated fumigation operators. However, it is very useful for all involved in the storage of food commodities and working in food manufacturing plants, to understand the principles and practical aspects, and constraints, of fumigation, so that they can consider or recommend fumigation only when it is likely to be the best option. At the time of writing, 2014, the Montreal Protocol has resulted in methyl bromide – previously the most frequently-used fumigant - being totally phased out from European and other developed countries’ fumigations. Sulfuryl fluoride (SF), previously confined to termite and other wood-boring insect control mostly in America, has now received limited approval for use on many timber products including logs, and for use in empty grain storage situations and emptied flour & feed mills. In the USA SF has a few dried foods clearances (tree nuts, for example) but not in Europe. The principle reason seems to be that there will always be a fluoride residue, and in many situations there is no accepted, listed approval for fluoride in foods, which helps explain why SF is generally unacceptable for food container imports. Phosphine (PH3) is the commonest fumigant in use worldwide. It has been available commercially since the 1950s, originally being produced solely in Germany, but in recent years also manufactured in India, some South American countries and China, in formulations very similar to those well known from Germany. Hot-Fogging tobacco warehouse A Detia Phosphine dispenser electrically- powered for silos. This uses spherical tablets which roll down a plastic tube and into the silo, and will result in a powder contamination of the fumigated grain 30 | March - April 2014 GRAIN&FEED MILLING TECHNOLOGYF
    • flat bottom silos hopper silos www.symaga.com symaga@symaga.com Offices and Factory: Ctra. de Arenas km. 2,300 13210 Villarta de San Juan • Ciudad Real- Spain T: +34 926 640 475 • F: +34 926 640 294 Madrid Office: C/ Azcona, 37 • 28028 Madrid - Spain T: +34 91 726 43 04 • F: +34 91 361 15 94 Bangkok. 8 - 10 AprilTashkent 2 - 4 April Bangalore, 23-25 April VIV India leader worldwide innovative R&D since 1985 92% export rate presence in 120 countries
    • of fumigation, so that they can consider or recommend fumigation only when it is likely to be the best option. At the time of writing, 2014, the Montreal Protocol has resulted in methyl bromide – previously the most frequently-used fumigant - being totally phased out from European and other developed countries’ fumigations. Sulfuryl fluoride (SF), previously confined to termite and other wood-boring insect control mostly in America, has now received limited approval for use on many timber products including logs, and for use in empty grain storage situations and emptied flour & feed mills. In the USA SF has a few dried foods clearances (tree nuts, for example) but not in Europe. The principle reason seems to be that there will always be a fluoride residue, and in many situations there is no accepted, listed approval for fluoride in foods, which helps explain why SF is gener- ally unacceptable for food container imports. Phosphine (PH3) is the commonest fumi- gant in use worldwide. It has been avail- able commercially since the 1950s, originally being produced solely in Germany, but in recent years also manufactured in India, some South American countries and China, in formulations very similar to those well known from Germany. Phosphine gas is invariably generated on- site by the action of atmospheric moisture, or commodity humidity, on solid aluminium, or magnesium, phosphide preparations, in tablet, pellet, sachet, plate or strip form. E.g.: AlP + H20 = PH3 + AlOH. Phosphine is a light gas (only slightly heavier than air) with a small very active mobile molecule. It has a wide spectrum of activity, but is a slow-acting fumigant on insects, needing days, rather than hours of exposure in most situations. It will easily leak out of all but the best-sealed enclosures, can damage through corrosion – silver phosphide - delicate silver, gold & copper fittings (e.g. computer equip- ment and switch boxes) and, if the loose pellets and tablets are used, leaves powder deposits of (mostly) aluminium hydroxide. Residues of the gas itself are almost impos- sible to detect in the commodity following normal aeration after treatment, but the dry powder residue is usually an unacceptable contamination in dry foods, so a “contained” formulation should always be chosen to facilitate complete removal [see later in this paper for illustrated examples]. Due to the corrosion risk when the gas is in contact with copper gold and silver, phosphine is not normally used for build- ings (electrical systems and computers) and never for aircraft (electronics). With great care it can be used in mills, by separating the gas from all computer-activated machinery – shrouding and separating with well-sealed polythene enclosures – almost the exact opposite of the fumigation procedure, where gas leakage is the big potential problem. Phosphine is not therefore a complete replacement for methyl bromide in all cir- cumstances. It also has a fire hazard poten- tial when very high concentrations occur – the critical auto-ignition level is 1.8% which equates to 18,000 ppm – significantly higher than would occur in normal fumigations. Concentration x Time [CTP] One of the most important features of all fumigations is the need to contain the gas within the fumigation enclosure at a specified concentration for a specified time (= the exposure period). These two factors can be varied within limits, provided the necessary concentration x time product is achieved. This value (the CTP) varies according to the pest species and live stages, and for mixed species infestations it will be necessary to chose the highest value quoted for the most “difficult” species. For Methyl Bromide this was a critical feature to achieve good kill and not cause excess bromide residues. But phosphine does not have these problems. It is much more common simply to decide the dosage, and measure the end-point concentration. Commodity fumigation in a warehouse If the store floor is in poor condition, it will be necessary to stack on a base or ground fumigation sheet. This can later be drawn up, rolled and joined (clips, clamps, glue or tape, according to the sheeting in use) to the main stack fumigation sheets. Since sealing is so vital to long-exposure phosphine fumigations, it may be difficult, or even impossible, to successfully fumigate normal warehouses, where the ridge is usually out of reach for any form of sealing. Ventilated silos and bins are frequently fitted with aerated steel floors which, again, are almost impossible to seal to form a gas-tight enclosure suitable for phosphine.. Not only this, but there are many grain stores which are just not suitable for fumiga- tion. In the days of 24-hour methyl bromide use, it may have been possible to achieve sufficient gas concentration to give a good kill. 5 to 15 day phosphine fumigations may not be possible, and it really is essential that the fumigator-in-charge makes this clear to the potential client Building fumigations (= ‘space fumigation’) The principles under which whole build- ings are fumigated are the same as for stacks: the gas must be contained at the correct concentration for the required time (exposure period) to allow the gas time to Spraying beetle-proof mesh – no gloves Hot-Fogging tobacco warehouse Smoke generator Spray grain store roof ; note lake of spray fallout for next grain to sit on Thick bubbles of tablet de-activation Real bulk grain fumigation – only the doorway was sheeted to the ground!! * Spraying beetle-proof mesh – no gloves Hot-Fogging tobacco warehouse Smoke generator Spray grain store roof ; note fallout for next grain to sit on Thick bubbles of tablet de-a Real bulk grain fumigation – only the doorway was sheeted to the ground!! * Tabs in first few minutes 100 AlP sachets in one roll – the original bag-blanket – quick and easy no masks required legally at the time! Bulk grain with cover sheet ready to pull over. * Bulk-bag of costly seed fumigated with PH3-no risk Some General Features of Fumigation Advantages: Disadvantages: Very penetrative into insects and mites, into food residues and spillage, through packaging and into foodstuffs and other materials, e.g.: timber Insect and mite tolerance to fumigants is reduced at higher temperatures Concentration, or time, can be varied, within limits, providing the final CxT product is sufficient for the species to be controlled High risk of gas leakage out of fumigation enclosures over long exposure Sealing and good condition sheeting is essential Overdosing of MeBr would kill fresh plant produce and cause high bromide residues. Phosphine does not have these problems No residual protection, therefore not a prophylactic treatment Gas distribution affected by stowage, temperature, absorption, commodity etc All involved must be trained to wear protective respiratory protective clothing. Not very expensive but vital for survival Measurement of gas concentrations throughout the fumigation is essential – check on instruments and detection tubes available Tabs in first few minutes Spray grain store roof ; note lake of spray fallout for next grain to sit on Real bulk grain fumigation – only the doorway was sheeted to the ground! 32 | March - April 2014 GRAIN&FEED MILLING TECHNOLOGYF
    • e lake of spray n activation
    • search out and kill the target pest. Sealing buildings is laborious, time-consuming (up to 2 days full work for a flour mill), and it will be necessary to do some pre-cleaning of machinery to ensure good penetration of the Fumigant But the gas at least changes - we men- tioned Sulfuryl Fluoride earlier – this is now the gas of choice for whole buildings. A Dow AgroSciences gas, supplied and used according to DAS safety and training standards. The quantity of gas needed for a mill could be considerable (usually several tonnes) and this will require careful planning to ensure safe de-gassing, or ventilation. Where phosphine can be filtered out using a mask and filter, SF cannot, so breathing apparatus is required, with the attendant training and understanding. All fumigations may leak gas, despite careful precautions. The success of the treatment will depend on knowing that the correct dosage has been used, and retained, throughout the fumigation exposure period. Taking gas concentration readings, using simple gas-detector tubes or electronic instruments or, in the case of SF, specialist equipment will be needed to monitor this. As SF is a cylinderised fumigant, additional gas may be introduced during a fumigation to “top up”, if leakage has occurs which can- not be fixed. Of course, reasons for leaks should be investigated; holes, tears and poor sealing should be repaired urgently where they are accessible. Is fumigation necessary? Fumigation is never a low-cost treat- ment. Although it has distinct advan- tages over other forms of pest control (for example, its ‘seek and kill’ of insects hidden within foods), it will not guarantee zero re- infestation. As with all forms of chemical pest control, there should be a justification for the use of pesticides. How does one justify the fumigation of food commodities? Interestingly, since Methyl bromide has disappeared, and SF is so relatively costly, many mills have adopted extra hygiene measures, and sometimes heat treatments, to achieve a similar degree of pest control. But, whilst fumigation and heat treatments have no prophylactic role, targeted hygiene does!!! So removing methyl bromide has had the effect of minimising the use of fumi- gation in mills, and simultaneously encour- aging a much more hygiene-conscious mill industry (though this industry may not see it quite like that!!) Acheta’s Fumigation Handbook Whilst I justify covering quite a bit of the older techniques (liquid fumigants, for example) because many older fumigators don't realise why they are no longer available, it also helps to put phosphine into perspective, and hopefully it will make all think twice - we have no other fumigant gases left if phosphine is pulled due to bad/unsafe practices. It can also take the place of the very old and out- of-date BPCA Fumigation Manual, which also covers many of the older fumigation methods, and is therefore also a source of historical reference. Pricing Individually @ £25, plus P&P (£3.00) £28 inc P&P http://www.acheta.co.uk . Each ‘plate’ enough for 20ft container * Tablet residue wet deactivation – wearing a mask with filter * 100 AlP sachets in one roll – the original bag-blanket – quick and easy no masks required legally at the time! Bulk grain with cover sheet ready to pull over. * Bulk-bag of cost risk Magphos Fumistrip –for large-scale fumigations. Each ‘plate’ enough for 20ft container * Tablet residues collected for disposal * Tablet residue wet deactivation – w Tabs in first 100 AlP sachets in one roll – the original bag-blanket – quick and easy no masks required legally at the time! Bulk grain with cover sheet ready to pull over. * Bulk-bag of cos risk Magphos Fumistrip –for large-scale fumigations. Each ‘plate’ enough for 20ft container * Spraying beetle-proof mesh – no gloves Hot-Fogging tobacco warehouse Smoke generator Spray grain store roof ; note lake of spray fallout for next grain to sit on Water deactivation of ALOH Zig-Zag MgP Fumistrip Bag-blanket on grain surface Spraying beetle- proof door mesh 34 | March - April 2014 GRAIN&FEED MILLING TECHNOLOGYF
    • tly seed fumigated with PH3-no wearing a mask with filter * few minutes stly seed fumigated with PH3-no
    • www.gfmt.co.uk LINKS • See the full issue • Visit the GFMT website • Contact the GFMT Team • Subscribe to GFMT A subscription magazine for the global flour & feed milling industries - first published in 1891 INCORPORATING PORTS, DISTRIBUTION AND FORMULATION In this issue: • Researching and reporting: the roller flour milling revolution • What is Fumigation? A technique of pest control using a toxic gas • VIV Europe preview Our pull out centre section March-April2014 • Bread is the foundation of civilization • Conserving grains: through drying • Flour miller values weighbridge technology on the island of Zanzibar first published in 1891 This digital Re-print is part of the March | April 2014 edition of Grain & Feed Milling Technology magazine. Content from the magazine is available to view free-of-charge, both as a full online magazine on our website, and as an archive of individual features on the docstoc website. Please click here to view our other publications on www.docstoc.com. To purchase a paper copy of the magazine, or to subscribe to the paper edi- tion please contact our Circulation and Subscriptions Manager on the link adove. INFORMATION FOR ADVERTISERS - CLICK HERE Article reprints All Grain & Feed Milling Tecchnology feature articles can be re-printed as a 4 or 8 page booklets (these have been used as point of sale materials, promotional materials for shows and exhibitions etc). If you are interested in getting this article re-printed please contact the GFMT team for more informa- tion on - Tel: +44 1242 267707 - Email: jamest@gfmt.co.uk or visit www.gfmt.co.uk/reprints