Heat treatment in pest control – the obvious alternative to toxic gases

Potentially lethal to humans, toxic gases have been used for many years to kill pests. But now food and timber industries across the world are looking to heat treatment as an effective and safer means of controlling insects. David Hammond, who developed the Thermokil heat treatment system, assesses the future of this method of control.

Heat treatment in action. Photo: Dave Hammond

For over 70 years toxic gases have been used around the world to kill a range of pests, from insects in commodities, timber, food production machinery and buildings to rodents in burrows. While undoubtedly effective, their place in society is being questioned as scientists assess their health and environmental side effects.

Range of toxic gases
A range of gases used for pest control has been phased out largely due to health concerns. These include cyanide, phosphine, methyl bromide, ethylene oxide, sulphuryl fluoride, and the liquid fumigants carbon tetrachloride (CTC), 1,2-dichloroethane (EDC), 1,2-dibromoethane (EDB). CTC, EDC, EDB, and ethylene oxide – and methyl bromide is following under the Montreal Protocol because it is an ozone depleter and a cancer risk to operators. Cyanide has been withdrawn largely because of its dangers, but also because of a lack of anyone prepared to pay for continued registration. Even the effectiveness of phosphine is being questioned due to widespread insect resistance resulting from misuse of the gas in the Far East and India. Here, operatives sometimes have released the gas into supposedly sealed stacks that need to hold lethal concentrations for over five days. Where the sheets used to seal stacks do not touch the ground insects are continuously exposed to repeated sub lethal doses. While many insects are killed, those most resistant survive to breed and produce a population of insects more resistant to the gas. This cycle repeats itself, gradually selecting more and more resistant insects.

An alternative 
Against this background, the simple fact remains that most proteins stop functioning above 45oC. Larger animals with higher water contents and an ability to regulate their body temperature can survive high temperature for short periods but insects are very vulnerable and die quickly. Using heat treatment as a means of control has massively reduced health and safety and risk assessment implications with minimal environmental implications. 
    Heat treatment comes in many forms with some big mills in the USA installing massive million dollar systems that heat entire buildings to 50oC. In Europe early work required buildings to be totally covered with insulated sheeting, but new heating technology reduces the need for this. In the UK progress has been slower against a strong methyl bromide lobby, but now many pest control companies such as Ecolab, Eleberts Pestforce, Precision Pest Management and PCT are using a heat treatment system designed by Thermokil.This system can treat food production machinery, empty food storage bins and silos, even whole buildings, without the client having to evacuate the site or even stop production. Treatments of infested food production lines can be carried out alongside working lines without risk. Heat treatment is not a panacea as food factories still have to work at good hygiene. But elimination of toxic gases from food production facilities has to be a good thing. 

How does heat treatment work?
In practice, a temperature of 50oC to 52oC needs to be maintained for one hour to kill most species of insect. As most bins and food production machinery are made of metal, a good conductor of heat, treatment is simply a matter of insulating the treatment area. This procedure is similar to that carried out during fumigation, except the seal does not need to be gas tight, so the plastic sheeting is easier and quicker to put in place. Temperature monitoring equipment is inserted to monitor heat distribution via a laptop, and application of the indirect burn clean air from powerful oil fired mobile heaters. Even wood and concrete conduct heat, although at a slower rate, so treatment of these items is also possible.

Development of technology
This Thermokil technology used in the UK was developed in conjunction with German engineering expertise and has spread to Australia and New Zealand where trial work has been carried out. Future introductions into Japan, Austria and the Nordic countries are in the pipeline. It is also now being applied to the heat treatment of timber for phyto-sanitary reasons under the requirements of ISPM15, the new international wood packaging marking scheme. Previously, huge quantities of methyl bromide were used and vented into the atmosphere in the fumigation of timber. Now this is mostly done with heat treatment, bringing incalculable environmental benefits.
    Generally, treatment of commodities with heat is not being pursued with the same vigour. However, there are commercially available systems for treatment of commodities in containers and barges with modified atmosphere techniques and CO2 in silos, and commodities can even be heat treated along moving conveyor systems. 

The future
By and large heat treatment companies around the world are small, without big marketing budgets, and are pitted against some of the biggest chemical companies in the world. As a result the food industry and governments are under pressure from lobbyists to allow new dangerous chemicals for fumigation. A classic example is the Dow Chemical Company introduction of the highly toxic sulphuryl fluoride (Profume) into Europe for fumigation of flourmills and other buildings.
    On the optimistic side, there is a genuine feeling that as links between many pesticides and cancer rates come to the fore in the media and with consumers, there is sufficient political will to support cleaner, safer forms of pest control. This will benefit all of us, and particularly our children.

Contact David Hammond heatinsect@yahoo.com for more information on heat treatment options around the world.  Please forward details of any new pesticide free treatment systems to PAN UK who support the growth in this developing field.

[This article first appeared in Pesticides News No. 67, March 2005, page 16]