Many British houses include wood in their construction – a food source for insects and fungi whose natural habitat is rotting trees but who have adapted to living in household timbers which are similarly damp, dark and still.
Houses constructed up to the First World War were generally built by skilled craftsmen using high quality timber that could be preserved indefinitely in the right conditions.
By the end of the Second World War, skilled craftsmen were in decline, many buildings had been damaged or neglected for years and a construction boom was under way – result – cheap housing thrown up using poor quality timber and with little concern for long-term timber preservation. Meanwhile the new chemical industry was producing cheap and effective pesticides to solve any pest problems.
However, over time the hazards of chemical pesticides became apparent. Pest control workers applying toxic chemicals on a daily basis, often in enclosed and badly ventilated places, blamed the chemicals for their increasing ill health.
Householders whose homes had been treated with chemicals experienced unusual symptoms, including sore eyes, nose and throat, coughing and sneezing, headaches, nausea, skin rashes and lethargy. In extreme cases victims suffered epileptic fits, developed rare cancers and blood diseases and even died.
However, it is not only the immediate health effect of pesticide exposure that is of concern but the long-term health and environmental effects.
For example, bat populations around the UK are known to have declined sharply as a
result of chemical timber treatment and the treatments may have affected populations
further by reducing the insect populations that bats feed on.
It is essential that pest problems are identified correctly
before any work is carried out.
All surveyors should be qualified to identify timber pests. (The Building Research Establishment [01923 664000, www.bre.co.uk] publishes a series of excellent digests which explain techniques for identifying timber problems.) All too often the pest is incorrectly identified either due to restricted physical access, or inexperience, and the assumption is made that comprehensive chemical treatment is needed.
Hutton and Rostron Environmental Investigations, who never use chemicals in their timber treatments, have trained search dogs, ‘rothounds’, to
locate dry rot in inaccessible spots. Check 01483 203221
The pests that attack
timber in buildings belong to two main groups: wood boring insects and fungal rots; they may occur in isolation or in combination as both like the same environmental conditions.
The most common wood boring insects are the larvae of the common furniture beetle, the house longhorn beetle, wood-boring weevils and the death watch beetle.
The adult beetles lay their eggs on the surface of the wood. When the larvae hatch they can tunnel through the wood for up to five years. However, they can be difficult to detect as holes in the wood may be from an old infestation so it is important to get specialist advice before any remedial work is carried out.
Many wood boring insects, such as the bark beetle, cause only minimal damage which does not effect the strength of the timber so do not need to be treated. Other beetles, such as weevils, are only attracted to decaying wood. Once the wood is dried and ventilated they will disappear and not return. Yet others are restricted to certain areas of the UK and certain types of wood.
Wood that is allowed to remain damp over long periods is commonly attacked by fungi, called ‘rots’, which decay the wood and can ultimately lead to its structural failure. They are divided into two main groups.
Dry rot is caused by Serpula lacrymans, a single, rather-misnamed fungus which can only survive in wood which has a moisture content above 20%.
Wet rot is a collective term for 13 different fungi that attack wood with a moisture content above 22%.
Neither rot can survive in dry, well ventilated conditions, and so, to eliminate them, the damp problem must be corrected. Chemicals will not prevent rot attack in damp timber. Central heating and a number of heat-treatment systems have been developed over the years to counter damp problems. Once the damp has gone, the damage to the affected timber may be assessed.
All timber attacked by rot should be cut away to one metre beyond the last sign of decay and replaced. 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 as environmental conditions can change, allowing pests to attack where they could not survive before.
Various wood preservatives can help to prevent pest attack. Synthetic preservatives contain pesticides, but coating wood with raw linseed oil will preserve it just as well.
All commercially available chemical wood treatment and preservation products are toxic to humans and animals. Knowledge of their toxicity is vital to ensuring the least toxic timber treatment.
Current EU legislation
Chemicals used in timber treatment in the UK are regulated by the Health and Safety Executive although, under EU harmonisation rules, products now must be considered under the European Biocidal Products Directive.
Suppliers and producers of wood preservatives have to ‘notify’ the European Commission which existing active substances they want reviewed for approval. Incomplete dossiers of information on the ‘active’ substances can cause substances to be removed from the approved list and so be withdrawn.
For example, chromium in wood preservatives is currently being removed from the EU market because sufficient supporting evidence for its safety could not be established.
Other products that have been withdrawn include copper chrome arsenate, creosote and bis(tributyltin) oxide.
Health impacts – toxicity
Acute toxicity is how much it takes to make a person (or animal) die or suffer symptoms of
poisoning after a single dose or multiple doses in a short space of time.
Chronic toxicity is the effect of long-term exposure to smaller doses eg cancer, birth defects and physiological disease.
Acute toxicity data is collated and assessed by the World Health Organisation International Programme on Chemical Safety. The WHO employ a widely used indicator of acute toxicity, the LD50; it shows what dose of undiluted chemical will kill 50% of a sample group of animals when administered via the mouth or skin. Only the active ingredient of pesticide products are assessed.
The chronic effects, however, for most of the products on the market, are less well understood and consequently the acute toxicity data for active substances is often relied upon. There are serious concerns about endocrine disrupting pesticides, such as tributlytin, but there is no comprehensive list of, and virtually no information about, many of these substances.
How to treat your timber
Pest problems exist where the environmental conditions are comfortable for them. All rots and several insects that attack wood must have some level of damp in order to develop. This 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 re-infestation once the chemicals become inactive or in places they were not applied.
Here are some key stages in addressing a timber pest problem.
Check for previous treatments
Thousands of unnecessary treatments are carried out because surveyors are not sure whether the problem has been treated before.
Identify the problem and the extent of damage
A qualified surveyor should be able to identify the presence of insect infestation or rot and the conditions that attracted the pests.
Treat any damp problems
Dampness is a precondition for rot or infestation and must be eradicated. It may come from the ground (rising damp), from above as rain (penetrating damp), or from the building or cavities within the building structure (condensation).
Each requires different treatment without the use of chemicals.
If treatment is necessary choose an effective treatment
Make sure the treatment is suited to the specific problem and will
minimise any potential toxicity to humans and animals.
Order the correct amount of chemicals to prevent waste
Ensure drums are stored carefully and unused chemicals and decayed timbers are disposed of correctly.
Replace timbers responsibly
Careful choice of timber species and use of good quality, well-seasoned timber protects forest environments and minimises the need for future chemical treatment.
Practise good maintenance
To prevent reoccurrence, check vulnerable timbers and adjacent materials regularly. Ensure that any timber that gets wet is able to dry out; fungi only attack timber that remains damp over a sustained period.
The Association for Environment Conscious Building and the Centre for Alternative Technology recommend inorganic boron as effective against wet and dry rot and insect infestations. It is also non-toxic to bats nesting in roofs as long as they do not come into contact with the wet chemical.
The Centre for Alternative Technology also suggests the use of heat-treated wood. The Finnish ThermoWood® Association steam-heats timber to reduce its moisture content and thereby the likelihood of attack from wet and dry rots. http://tinyurl.com/5969cr
A European company, Thermo Lignum, uses heat technology and oxygen starvation to destroy pest infestations in any organic material, including wood, textiles, paper and museum artefacts. No toxic chemicals are used, so no damage is caused to the materials.
The Thermo Lignum system is widely used in museums and art galleries although it is rarely suitable for domestic homes as the disruption of completely emptying the home has proved to be too much. However, it is used on reclaimed materials (such as old floorboards) and antique furniture and, with rising moth infestations, there have been increasing demands for treatment of textile products. 020 8964 3964 www.thermolignum.com
Finally, the Association for Environment Conscious Building will give advice on environment-friendly preventative and remedial timber treatments, and may be able to recommend builders who use these methods. 0845 4569773 www.aecb.net/faq.php
Pesticide information available:
Pesticides on a plate: a consumer guide to pesticide issues in the food chain.
A simple overview for a non-technical audience on what pesticides are and the hazards they pose, with a focus on pesticide residues in food. It includes:
• How farmers and farm workers can be
affected, particularly in developing countries.
• The costs society pays for pesticide problems.
• The role of supermarkets in our current levels of dependency on pesticides.
• How food supply chains could work to reduce pesticide use.
• Some good news stories on pesticide
reduction in agriculture.
• Ideas for action for the concerned individual.
• Lists of resources and further reading
The booklet is suitable for community groups, students, consumer groups and the public.
It can be downloaded from the PAN UK website at www.pan-uk.org/Projects/Fairness/
or hard copies can be obtained from PAN UK
56-64 Leonard Street, London EC2A 4LT.
Pesticide Exposure and your health
PAN UK’s Pesticide Exposure (PEX) project is for people
affected by, or concerned about, pesticide exposure. Pesticides are designed to kill pests so it is not surprising that they can also be highly toxic to humans. People may be exposed to pesticides through the use of domestic pest control or gardening products, or through spray drift from pesticides used on fields, parks or pavements.
In the UK, acute pesticide poisoning is thankfully rare (though not unheard of). However, the effects of chronic exposure to low levels of pesticides are unclear. Studies have linked pesticides with cancers, Parkinson’s disease, asthma and reproductive problems. PAN UK also speaks to many people who experience severe ME like symptoms following exposure. However, it’s very hard to link a particular health problem with a particular chemical. GP’s may be unfamiliar with pesticide poisoning, and those affected may face difficulty in obtaining a diagnosis and treatment.
PEX provides an information service and quarterly newsletter for anyone who is concerned about the effects of pesticide exposure. Those affected can also make contact with others for mutual support. The PEX project also collects case studies to inform and support PAN UK’s work of trying to reduce pesticide use and impacts in the UK.
For more information on the PEX project please call
Ruth Beckmann on 020 7065 0914 or email
Click here for more general articles on asthma
First Published in 2008
Top of page