Least toxic timber treatment

Dry rot, wet rot and many wood boring insects will only occur in damp timber. Solve your damp problem and you have gone a long way to solving your pest problem.

One of the most common requests which the Pesticides Trust [now PAN UK] receives from members of the public concerns the least toxic method of treating woodworm and rot. Householders rightly or wrongly fear serious structural damage to their property from timber pest attack, and there are plenty of commercial companies which offer various remedial services to control and prevent pest attack.
    The whole area of timber pests and their treatment is complex, and there is no simple answer which is satisfactory for every inquirer. However many pest control and timber treatment companies are only too willing to provide simple solutions based on chemical pesticides.
    The purpose of this paper is to inform members of the public that chemical pesticidal treatment of timber pests in homes or workplaces is always toxic. Such treatment may not be necessary at all and there may also be a non-toxic or less-toxic alternative available. We will also include some information on the hazards associated with the chemicals most commonly used in timber treatments in the UK. Together we hope that this information will allow people to make informed choices about the way in which their particular problems are dealt with.

Background
Many British houses incorporate some timber in their construction. Since wood is an organic material it can be a source of energy for other organisms such as insects and fungi which have adapted to feed upon it. The organisms which live on wood in houses generally evolved in order to exploit fallen rotting trees on the forest floor, and have simply infested timber in houses where similar conditions of damp, darkness and still air exist.
    Houses constructed up to the time of the First World War were generally built by skilled craftsmen who understood that high quality timber could be preserved indefinitely if the right environmental conditions were maintained. By the time the Second World War had ended, there were fewer skilled craftsmen, many existing buildings had been damaged and neglected for years, a construction boom was underway resulting in quick cheap housing being thrown up with little or no concern for long term timber preservation, lower quality timber was being used in construction and the new chemical industry was producing cheap and effective new pesticides which could quickly solve any pest problems which arose.
    As the hazards associated with chemical pesticides became more widely acknowledged, many pest control workers who were applying some extremely toxic chemicals on a daily basis, often in enclosed and badly ventilated places, linked the symptoms which they were experiencing with pesticide poisoning. Householders who had applied timber treatment chemicals in their homes, or whose homes had been professionally treated, also experienced unusual symptoms. These included sore eyes, nose and throat, coughing and sneezing, headaches, nausea, skin rashes and lethargy. In some extreme cases victims suffered spasms which were diagnosed as epilepsy, and others developed rare cancers and blood diseases. Some very unfortunate cases of exposure to timber treatment pesticides have resulted in death.
    The Sunday Telegraph newspaper recently reported that a Court of Appeal had ruled against a family who have been sensitised to chemicals from previous pesticide exposure, and ordered them to vacate their home in order for dry rot to be treated with permethrin and carbamates against their wishes(1). This follows the case of Margaret Reichlin, from near Andover in southern England, who suffered ill health effects after a waterproofing treatment may have caused leaching of previously applied wood preservatives, costing her in total £26,000 in remedial work (see Pesticides News No. 38 p.8). Recent scientific research suggests that using toxic chemicals in the home should be questioned and alternatives sought, for example:

• A 1998 occupational study on a male workforce involved in wood preservation suggested that chlorophenol exposure may increase the risk of soft tissue sarcoma(2).
• In 1997, Clyde Hertzman and his co-workers found that there was an increased risk of non-Hodgkin's lymphoma associated with chlorophenate wood preservative exposure among sawmill workers. Chlorophenate was widely used in British Columbia, Canada as a fungicide between the 1940s and 1989 when its use was discontinued(3).
• Results from a study in Germany that investigated the adverse effects of wood preservatives used in daycare centres showed a significantly reduced birthweight and length in the offspring of females exposed to non-pesticide organochlorines, pentachlorophenol (PCP), and lindane and indicated that a toxic effect might have effected the foetus(4).

In addition to the human health hazards of timber treatment chemicals, bat populations around the UK declined sharply as a direct result of the chemical treatment of roof void timbers against pests.
    The chemical and pest control industries make their living from spraying pests with chemicals. They have a vested interest in having buildings treated with their products and services. Often remedial damp work will be offered in conjunction with pesticidal treatments by the same companies who also employ surveyors to convince home owners of the need for their services.
    Solving a damp problem in any building is essential, and this must be the first step in any timber pest treatment strategy. This might include for example injecting chemical damp proof courses (DPC) into external walls, roof repairs and window and door seals. Timber pest control without adequate damp proofing is pointless and is not likely to work for long. Be careful in the choice of chemical damp proof courses as solvent based ones have caused health problems. Water based DPCs present less of a hazard.
    There are also strong arguments which support the theory that the chemical treatment of timber pests is less effective, more expensive and more dangerous than alternative traditional methods. These include management of the physical environment in terms of damp, ventilation and temperature, replacement of severely damaged timber, and use of materials and building techniques which reduce the risk of future pest attack.

Chemical control
The commercially available chemicals which are most commonly used in timber treatments are all approved by the Health and Safety Executive in accordance with the Control of Pesticides Regulations (1986). Products are registered under these regulations for sale and use as wood preservatives and are all toxic to humans and to animals to one degree or another. Some have been clearly identified as causing serious long term health effects including cancer and reproductive problems. However, their correct and safe use in accordance with label instructions and legal requirements should not normally endanger the health of people or non-target animals.
    Each commercial product will consist of one or more diluted active ingredients in a formulation of other ingredients. It is the active ingredients which effectively kill the pest while other chemicals in a commercial product will help to make the active ingredients effective at carrying out their job.
    The toxic effects of chemicals include its acute toxicity ie how much it takes to make a person or an animal die or suffer symptoms of poisoning, and the effects of long term exposure to smaller doses ie carcinogenicity, birth defects, physiological disease etc. A widely used indicator of acute toxicity is the LD50; It shows what dose of undiluted chemical will kill 50% of a sample group of an animal (usually mouse or rat) when administered via the mouth (orally) or skin (dermally) It is the active ingredients which generally have the most serious toxic effects, and some of these are briefly outlined below for those most frequently found in timber treatment chemicals.

Table 1. Concerns about timber treatments used in the UK(5, 6)
2-phenylphenol (LD50 = 2480) mild skin irritant, endocrine disruptor, toxic to fish
3-iodo-2-propynyl-n-butyl carbarmate (LD50 = 1470) cholinesterase inhibitor
carbendazim (LD50 = 10000) endocrine disruptor
copper sulphate (LD50 = 300) weight loss, kidney and liver damage
cypermethrin (LD50 = 250) endocrine disruptor, mild skin and eye irritant, possible skin sensitizer
lindane (LD50 = 76) very toxic orally, skin, eye and respiratory tract irritant, evidence of chronic disease, carcinogenicity and mutagenicity
pentachlorophenol (LD50 = 80) foetotoxic, skin and eye irritant
permethrin (LD50 = 500) endocrine disruptor, mild skin and eye irritant, skin sensitizer
pirimiphos-methyl (LD50 = 2018) cholinesterase inhibitor, mild skin and eye irritant
sodium fluoride (LD50 = 180) highly toxic
tributyltin oxide (LD50 = 224) irritating to skin, eyes and respiratory tract, considered to be teratogenic
acypetacs zinc (LD50 = 1935
azaconazole (LD50 = 308)
benzalkonium (LD50 = 400)
borax (boric acid, boric oxide, sodium tetraborate, disodium tetraborate) (LD50 = 4500)
dichlofluanid (LD50 = 5000)
furmecyclox (LD50 = 3780)
oxine copper (LD50 = 10000)
propiconazole (LD50 = 1520)
tebuconazole (LD50 = 4000)
tributyltin naphthenate (LD50 = 224
The LD50 shows the dose of chemical that will kill 50% of a sample group of animals, in this case it applies to rats dosed orally.

There is little information in the public domain on the following two columns of active ingredients registered for use as timber treatment products in the UK.

The pests
Pest problems exist where the environmental conditions are comfortable for them. For example, all rots and several insects which attack wood must have some level of damp in order to develop. This often means that by correcting a structural problem which allows damp conditions to exist, the pest problem can be solved too. Conversely, chemical treatment of the pest problem without solving the damp problem will often result in reinfestation of the damp wood once the chemicals have become inactive, or in places where the chemicals were not applied to.
    The pests which attack timber in buildings belong to two main groups: wood boring insects and fungal rots. Each of these pest problems may occur in isolation or in combination with others. It is not unusual for example, to find common furniture beetle Anobium punctatum infestation in conjunction with a rot since the environmental conditions which both types of organisms like are very similar.
    In discussing potential chemical treatments for timber pest infestation it is important to recognise that each pest may require a specific type of treatment and it is therefore vital that the problem is correctly identified before any treatment is carried out. Treatment companies should be able to identify the pest but often don't for various reasons which may include restricted physical access, inexperience, or the assumption that the presence of any pest requires comprehensive chemical treatment. Surveyors should have a Certificate of Timber Infestation Surveyors (CTIS) from the Institute of Wood Science, which qualifies them in the identification of timber pests. The Building Research Establishment(7) (BRE) also publishes a series of excellent digests which explain and illustrate clearly how to identify the different pests.
    All buildings should be regularly inspected for the presence of timber pests even if remedial or preventative treatment has been applied. Environmental conditions can change as a result of structural degradation, thereby allowing pests to attack where they could not survive before.

Insects
The most common wood boring insects are the larvae of certain beetles. The adult beetles lay their eggs on the wood surface, and when the larvae hatch they bore into it. The larvae tunnel through the wood for up to 5 years before they pupate, and emerge a number of weeks later as adults. The holes in the surface of wood which identifies an insect presence are those through which the adult beetles emerge.
    Spotting holes in the surface of wood does not necessarily mean that there is an active infestation. It certainly does not mean that the structural integrity of the building is threatened. It may well be that the holes remain from an old infestation which has long died out. Before any work is carried out it is therefore important to ensure that the infestation is active. One good indicator to look for is the presence of small amounts of clean sawdust under the emergence holes. BRE digest 307 is helpful in the identification of insect timber pests.
    Many wood boring insects only cause minimal damage which does not effect the strength of the timber, many will also disappear once the environmental conditions which attract them are changed. The few insects which are capable of causing serious structural damage only do so when infestations are severe. In addition some insects are largely restricted to certain areas of the UK and some only attack particular types of wood. These factors add to the importance of correctly identifying the suspected pest in your building before any treatment is carried out.
    Correct identification of the pest will include recognition of the environmental conditions which have attracted it. Correction of the environmental conditions will generally prevent further development of the pest.

Rot
Wood which is allowed to remain damp over long periods is commonly attacked by fungi which decay the wood and can ultimately lead to its structural failure. These fungi are commonly termed 'rots' and are divided into two main groups:

Dry rot - caused by Serpula lacrymans a single fungus which is rather misnamed since it can only survive in wood which has a moisture content above 20%.

Wet rot - a collective term for 13 different fungi which attack wood with a moisture content above 22%.

Neither dry nor wet rots can survive in dry, well ventilated conditions. In order to prevent their attack or further development the damp problem must be corrected. No amount of chemicals will prevent rot attack in timber which continues to be affected by damp.
    In addition, modern heating systems often reduce the moisture content of structural timbers to well below the levels in which rot can survive.
    The dry rot fungus is particularly sensitive to relative increases in temperature which has resulted in the use of whole building heat treatments. Heat treatment ensures that the organism is rapidly killed at the start of the control procedure and although active pores still exist, an appropriate drying regime should ensure they do not germinate.
    Once the damp problem has been dealt with, the extent of damage to the affected timber may be assessed. All timber attacked by rot should be cut away to one meter beyond the last sign of decay and replaced.
    This effectively means that no chemicals should be necessary since physical removal of the rot, together with damp prevention will prevent further fungal attack.
    All buildings should be regularly inspected for the presence of timber pests even if remedial or preventative treatment has been applied. Environmental conditions can change as a result of structural degradation, thereby allowing pests to attack where they could not survive before.
    Various synthetic and natural wood preservatives can help to prevent pest attack. Synthetic preservatives contain pesticides, but a safe traditional preservation method entails coating wood with raw linseed oil.

Who should treat my timber pest problem?
A qualified surveyor should be able to identify the presence of insect infestation or rot as well as the environmental conditions which have attracted the pests. Use an independent surveyor who has a Certificate of Timber Infestation Surveyors, rather than one who is linked to a damp proofing or timber treatment company. If the presence of the pests of damp conditions are suspected but not confirmed because of restricted access it is important to check these suspicions by making access before any remedial work is carried out.
    Damp proofing and timber treatment companies abound. They have a healthy commercial interest in carrying out as much work as possible at maximum cost to the client and minimum expense to themselves. This almost inevitably means extensive chemical treatment at the slightest sign of any pest presence, which should be carried out in conjunction with remedial damp-proofing. If used it is worth checking that a company is a member of the British Wood Preservation and Damp Proofing Association (BWPDPA(9)) which tries to maintain high professional standards and eliminate 'cowboys'.

Questions to ask and points to check

• A clear diagnosis of the problem, its extent and the reason it developed.
• Has the house been treated for timber pests before and when?
• Is the pest still active? - ask to see evidence of this.
• What has been done to correct the cause? eg damp proofing, ventilation etc.
• Is there any real structural damage that demands remedial work?
• Will damaged timbers be replaced?
• What other treatment is proposed beyond structural repair?
• If chemical treatment is suggested - which chemicals will be used?

Avoid lindane, PCP and TBTO

• Is the applicator trained? Is s/he using personal protective equipment?
• Is the company a member of the BWPDPA?
• Does the chemical treatment proposed match the diagnosis or is it a general 'cure-all' treatment (which should be avoided).
• How will the chemical be applied? Solid rods and pastes are better than liquid sprays and smokes.
• All dust should be removed from the area to be treated (sprayed dust can carry chemicals into other parts of a building).
• If roof spaces are to be treated, ensure water tanks are sealed before, or thoroughly cleaned after spraying.
• Ensure that a permanent label clearly showing the date, type and purpose of the treatment carried out be nailed or stuck in a conspicuous place to avoid unnecessary re-treatment in the future.
• Ask how long you should stay out of treated buildings or rooms, and remember pets too.
• Ensure that all chemical containers and contaminated equipment are removed.
• Get a guarantee for the work.

Unfortunately there is no legal requirement for timber treatment contractors to undergo any training or hold any certificates. They merely have to be 'competent' at their job and not put other people at risk from exposure to pesticides. There are other legal requirements relating to the use of pesticides which contractors should be aware of and comply with. These include an initial assessment as to whether a pesticide is needed at all, and selection of the least dangerous pesticide for the job.
    All chemicals used in timber treatment must be licensed by the Health and Safety Executive (HSE). Some are licensed for professional use and others for amateur use although since 'professionals' need no official certification, effectively anyone can use professional products. This also means that any householder, builder or entrepreneur can carry out remedial timber treatment using pesticides so long as they follow the label instructions and are 'competent'.
    The Association for Environment Conscious Building(10) will give advice on environment friendly preventative and remedial timber treatments, and may be able to recommend builders who use these methods. Hutton and Rostron Environmental Investigations Ltd(11) provides professional advice on remedial work without using chemical pesticides. The company also employs a variety of non destructive survey techniques for investigating inaccessible areas.

Comment
Once again the question of whether a building needs treatment at all must be asked. It has been found by The Remedial Treatment Unit at South Bank University that many different pesticides can be present in a property indicating past treatments. The insecticides DDT, dieldrin, lindane and permethrin and fungicides PCP, TBTO and glycol borates can be found in various combinations and the synergistic effects of exposure to these ingredients will possibly be greater than the sum of their effects taken independently(12).

References
1. Court ruling forces pesticide family to flee, The Sunday Telegraph, 24 January 1999, p16.
2. Jane A. Hoppin, Paige E. Tolbert, et. al., Occupational chlorophenol exposure and soft tissue sarcoma risk among men aged 30-60 years, American Journal of Epidemiology, 1998, Vol. 148, No. 7, 693-703.
3. Clyde Hertzman and Kay Teschke, et. al., Mortality and cancer incidence among sawmill workers exposed to chlorophenate wood preservatives, American Journal of Public Health, 1997, Vol. 87, No.1.
4. Wilfried Karmaus and Nicola Wolf, Reduced birthweight and length in the offspring of females exposed to PCDFs, PCP, and lindane, Environmental Health Perspectives, 1995, Vol. 103, No. 12, 1120-1125.
5. Pesticides Trust [now PAN UK] Active Ingredient Database, 1998.
6. Pesticides 1998, Your guide to approved pesticides, UK Health and Safety Executive, 1998, 571pp.
7. Building Research Establishment Ltd., Bucknalls Lane, Garston, Watford WD2 7JR, Tel 01923 664000.
8. Thermo Lignum, 10 The Grand Union Centre, West Row, London W10 5AS, Tel; 0181 964 3964.
9. British Wood Preserving and Damp Proofing Association, Building 6, The Office Village, 4 Romford Road, Stratford, London E15 4EA, Tel 0181 519 2588.
10. Association for Environment Conscious Building, AECB, Nantygrreg, Saron, Llandyful SA44 5ES, Tel 01559 370908.
11. Hutton and Rostron Environmental Investigations Ltd., Netley House, Gomshall, Surrey GU5 9QA, Tel 01483 203221.
12. Jeff Howell, Investigation of the numbers of repeat chemical timber treatments in homes, The Remedial Treatment Unit at South Bank University, London, April 1998.
13. Timbercheck, 26 Harling Bank, Kirby Lonsdale, Carnforth, Lancs LA6 2DJ, Tel 015242 71769.

[This is an extended briefing of an article that first appeared in Pesticides News No. 43, March 1999, p18-19]