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Intermediary October 2003
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Dr Tim Moss and Dr Daniel Sheard of Brookes Bell Jarrett Kirman are regularly instructed in cases involving insect infestation and the fumigation of cargo. This article examines how fumigants should be safely and effectively used to avoid potential legal problems. It concludes by explaining the proliferation of resistant strains of insects.
Damage to grain by insects is encountered in every grain-producing country. To reduce this damage, pesticides must be deployed to control the insect population. Fumigants are pesticides administered in gaseous form. They have established themselves as an effective and flexible tool in this process. Compared to other formulations, fumigants have a distinct advantage in that they may be effectively applied to large bulks of stored grain. The gas can permeate commodities that other formulations cannot, and this is ideal for use in cargo holds. The most widely used fumigant on ships is phosphine. This is administered by placing solid preparations containing aluminium or magnesium phosphide on or beneath the cargo surface, which react with atmospheric moisture to produce phosphine.
SAFE FUMIGATION
The IMO publication "Recommendations on the Safe Use of Pesticides in Ships" (forming part of the supplement to the IMDG Code (2000 Edition)) outlines provisions essential for safe fumigation. Every master who is due to load a cargo to be fumigated must be completely familiar with the current edition of this document. In this section of the article some of the more important provisions of the IMO Recommendations are examined.
i) Fumigation continued in Transit
If fumigation is to be conducted entirely in port or anchorage, then the IMO Recommendations state that the ship must be vacated by the crews. However, if fumigation is to be continued in transit, it is a fundamental requirement that this can only be conducted at the discretion of the master. If the decision is taken to continue fumigation in transit, then at least one officer and one crew member should be trained by the fumigator-in-charge. These trained representatives are responsible for monitoring the fumigant and maintaining safety for the duration of the fumigation at sea. Also, suitable respiratory protection and gas detection equipment must be on board and the crew should be aware of relevant first-aid procedures.
ii) Importance of Gas-tight Cargo Spaces
The IMO recommends that the fumigator-incharge and a trained representative of the master, or other competent person, should determine if the empty cargo spaces can be made sufficiently gas-tight before loading commences. This is essential: fumigant leakage poses a considerable danger to human health. In this regard, acute phosphine intoxication has been implicated in the deaths of a number of seamen. Also, if holds are not adequately sealed, then the correct dose of the fumigant might not be delivered - and the fumigation could be unsuccessful. Sometimes the design of a ship will make it inappropriate to fumigate a hold. For example, a ship which we have attended had an access fitted between a cargo hold and a passageway in the accommodation. If even a small leak had occurred, then intoxication or even the death of crew members could have resulted. We have heard of cases in which a number of fatalities have occurred as a result of the accumulation of fumigant that had subsequently leaked via unplugged hatch coaming drains in confined spaces. If the fumigator-in-charge considers that the risk of fumigant leakage is unacceptable, then he should not conduct fumigation of that space. Moreover, he should provide the master and other interested parties with a signed statement regarding his findings.
iii) Fumigant Dispersal
Following application of the fumigant and having carried out the necessary checks, the fumigator should provide instructions to the master regarding fumigation dispersal. Dispersal by ventilation will be prescribed by the fumigator to take place after a certain exposure time. The IMO recommends that a minimum of 24 hours before arriving in the discharge port, the master informs the relevant authorities that fumigation in transit has been conducted.
iv) Residue Disposal
The IMO recommends that instructions on correct disposal of the residues are provided by the fumigator. When phosphide has completed reacting, it forms a relatively inert residue of aluminium or magnesium hydroxide. However, even after a long exposure time, unreacted phosphide can still be present within the preparation residue, which will continue to produce phosphine. Also, if the residues are handled with bare hands, the phosphide can react with moisture in the skin to cause burns.
v) Fire Risks
In addition to general procedural knowledge, the fumigator-in-charge should be familiar with the properties of the fumigant and should communicate this knowledge to the relevant crew members. With phosphide application for example, in addition to the toxic risks, there is a hazard of fire. If the solid preparation is wetted, then the rate of reaction is increased and the heat created can be sufficient to cause fires or even explosions.
EFFECTIVE FUMIGATION
i) Correct Concentration
Although IMO Recommendations supply valuable information regarding fumigation procedures, there is little information regarding the use of specific fumigants. Applying the proper concentration of fumigant to the cargo space for the correct duration is essential in ensuring an effective fumigation, and this is the responsibility of the fumigator-in-charge.
ii) Placement of Fumigants
Fumigants do not necessarily diffuse homogeneously within a hold, and may have to be strategically placed in order for the correct dose to reach all parts of the stow more quickly. For example, the United States Department of Agriculture (USDA) Fumigation Handbook prescribes considerably longer exposure times following placement of phosphide tablets on the commodity surface than those placed several metres beneath the stow surface. The USDA do not recommend surface placement on any commodity greater than twelve metres in depth.
ii) Temperature
The effect of temperature on fumigation efficacy is well understood. At lower temperatures, insects are less active and therefore the rate at which they take up the fumigant is reduced. Also, absorption of the fumigant by the cargo is increased while the rate of diffusion of the fumigant within the commodity will decrease. These effects will combine to necessitate an increase in the dose required for effective fumigation. In general, fumigation conducted at lower cargo temperatures requires longer exposure times. A major producer of a phosphide formulation stipulates that their product should not be used when a commodity's temperature is below 5° C.
THE RESISTANCE PROBLEM
We have recently been involved in cases where fumigant concentrations were directly measured in a cargo space. The results showed that the correct dosage of phosphine gas had been maintained for the required duration. Nevertheless, significant productions of live insects had survived. In our view the most likely explanation of these results may be pesticide resistance. In a situation analogous to the rise in bacterial resistance to antibiotics, fumigant resistance is thought to be caused by inefficient fumigation: such fumigation provides a selection pressure that results in the survival of more resistant strains of insects and their subsequent proliferation. Several scientific studies have demonstrated the existence of certain strains of insect species, including the frequently encountered Tribolium spp., resistant to a variety of fumigants, including phosphine. If the practices of fumigation aboard ships cannot be adapted to the increased resistance of insects to pesticides, then a considerable increase in infestation problems can be expected in future years.
Our thanks for this article go to Brookes Bell Jarrett Kirman, www.brookesbell.com