Dr Laurie Cookson
* CCA
* Restrictions and regulations
* Treatment and fixation
* The arsenic in CCA
* Leaching
o Crops
o Mulch
*Animal contact
* Food storage, drinking water
* Working with treated wood
* Some safety tips
* Disposal of treated wood
* Existing structures
* CCA safety overview
* Alternatives to CCA
* What is Ensis doing?
* Footnotes and references
CCA (copper chromium arsenic) is Australia's most widely used wood preservative. It has been used safely in Australia for 50 years, and some 120 treatment plants are currently operating around the country. CCA treatment is effective - for example, extending the life of a radiata pine post from a few years to 40 years or more - and relatively inexpensive.
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Partial or complete restriction of CCA occurs in a number of countries, including Japan, Indonesia, Sweden and Germany. In the USA, CCA cannot be used in the domestic or home market.
In Australia, CCA preservatives are regulated by the Australian Pesticides & Veterinary Medicines Authority (APVMA). Recently, the APVMA implemented a number of restrictions on CCA that will take effect after March 2006. The main implementation affecting the public is that CCA will no longer be used to treat timber for structures where there is frequent and intimate contact, i.e. playground equipment, picnic tables, handrails, decking boards, garden furniture and exterior seating.
The main concern with CCA is that it contains arsenic, which while not a mutagen, acts as a carcinogen when ingested at rates above certain tolerable limits. The cancers it may initiate are skin and liver cancers. The safe or tolerable amounts of arsenic that can be ingested by humans has been determined quite accurately, because unlike most other pesticides, arsenic occurs naturally and can be found in relatively high levels in the drinking water of some towns in Bangladesh, Japan, Argentina and Taiwan. Extensive research has shown that arsenic is not a carcinogen and is safe or tolerable to ingest at rates below 2 µg/kg of body weight per day (World Health Organisation limit), or 3 µg/kg bw/d (Food Standards Australia limit). Indeed, arsenic is the 20th most common element on earth, so the ability for animal life to cope with some level of arsenic is to be expected.
It is important to note that the restrictions applied by the APVMA have occurred as a precaution. The majority of uses for CCA have not been restricted, and include industrial and commercial uses, agricultural and farm posts and marine applications. A link between handling CCA-treated timber (using recommended procedures) and cancer has not been demonstrated, as the potential ingestion rates of arsenic that can be calculated from valid available research are well within tolerable limits. Similarly, the latest review by ERMA in New Zealand (1) did not find increased health risks from using CCA-treated timber; consequently, no restrictions in that country were instigated. Nevertheless, the APVMA felt that more studies were needed to support the continued use of a potential carcinogen in high human contact applications, and that without those studies it should be restricted.
In Australia, treatment levels for CCA are set down by Australian Standards, (2) and by State legislation in Queensland and NSW. Only dedicated commercial treatment plants have access to CCA solutions. Unlike preservatives such as creosote, liquid CCA is not available to the public at hardware stores.
The approved CCA loading depends on the 'hazard' to which the timber will be exposed, expressed in the 'hazard classes' H1 to H6. The timber used most commonly for domestic purposes is in classes H3 (outdoor above-ground timbers such as decking, fence palings, fascia etc) and H4 (outdoor in ground contact, e.g. posts). Wood treated according to the Standard should carry a stamp or brand, indicating the hazard level to which it was treated. Other numbers in the brand are codes for preservative type and treatment plant number. Labels will also carry the words "Treated with copper chrome arsenate" after March 2006.
In CCA treatment, timber is impregnated with the preservative solution using controlled vacuum/pressure processes. The roles of the ingredients are: copper to control fungi, arsenic to control termites, and chromium to fix the copper and arsenic in the wood. More recent research at Ensis has shown that arsenic is not needed for the control of termites or marine borers (copper chromate does this) (3). Instead, the main benefit of arsenic is to inhibit certain copper-tolerant fungi. The correct combination or ratio of these elements as described under Australian Standards is critical to the performance of the product.
The fixation process ensures that virtually all the CCA becomes chemically bonded within the wood structure. The rate of fixation is dependent upon temperature. In warm conditions fixation may be complete within a few days, while in cold conditions it can take several weeks. Well-proven accelerated fixation methods are in use, such as steam conditioning. Producers are obliged (and after March 2006 will be required) to ensure that the product is adequately fixed before dispatching it from their sites. The CCA solution is orange, but turns green on fixation to give treated timber its familiar light green colour.
Arsenic occurs naturally in the soil, at concentrations in Australia of between 0.2 and 50 parts per million (=mg/kg), with an average of 5-6 ppm. The arsenic used in CCA is in a form - arsenate or pentavalent arsenic - that is five to ten times less toxic than the most toxic form, arsenite (trivalent). Fixation modifies the arsenate into metal-metal complexes and organo complexes with wood. Ingestion studies with animals have shown that this greatly reduces its mammalian toxicity.
For example, no evidence of toxicity was found after beagle dogs were fed 10 grams of CCA-treated sawdust per day for 5 days in food. Seventy percent of the arsenic passed with wood through the faeces. The rest was expelled with urine, having been extracted from wood in the stomach. The bulk (85%) of this urinary arsenic was detoxified to dimethylarsinic acid (4). In another experiment, researchers in New Zealand found no abnormalities after sheep and calves were fed 454 grams of CCA-treated pine once or 113 grams per day for 25 days (5).
Studies sometimes find slightly raised arsenic levels in the urine of some CCA treatment plant workers. However, no significant differences in medical history, compared with 'control' groups not associated with CCA, were detected (6), (7).
The majority of the CCA fixed within timber remains there over its lifetime of service; if it did not, the wood would rot and fail in much less than the 30-50 year period for which it is often guaranteed. However, a small amount of leaching inevitably occurs. This can show up in small rises in arsenic levels in the soil close to posts and poles. Studies have found levels return to normal within about 100 mm of posts and 150-200 mm of poles or decking. Simple precautions, such as those described below, can be taken to minimise any perceived risks from leaching.
* Crops
A number of studies have shown that CCA is not absorbed into above-ground food crops such as grapes (8), tomatoes and cucumber. There are, however, some reports of a slight increase in arsenic content in root crops such as carrots and beets grown against treated timber, although the arsenic is in a safe organic form and most of it is removed with peeling. Any possible concern can be eliminated by growing these vegetables more than 100 mm from treated-timber garden edgings, or by lining the edgings with plastic. This has the additional useful effect of reducing soil contact with the wood, which could further extend the wood's life.
* Mulch
Use of treated timber - sawdust or chips - as mulch is not recommended because of uncertainty about where the CCA will end up in the long term. Also, Australian Standards have low tolerances for heavy metals in mulch, and these may be exceeded with the addition of CCA-treated residues. Interestingly, one study (9) found soil with CCA-treated sawdust mixed in as an amendment gave higher yields of lettuce and beetroot than soil without sawdust or with untreated sawdust. Sawdust increased the soil's water-holding capacity, and this effect lasted longer with treated sawdust because of its slower degradation.
Using treated wood shavings for animal bedding is not recommended, despite suggestions from some studies that it can reduce the exposure of animals to disease-causing microorganisms that inhabit untreated bedding.
CCA-treated posts are widely used in farm fencing without problems. However, because CCA formulations tend to be 'salty', horses in particular may chew the timber. This activity does not appear to affect their health, but can ruin the fences. Modern oxide formulations of CCA are less salty, and hence probably less attractive to horses. Creosote-treated timber (unpleasant taste) is a common alternative in fencing for horses. If CCA-treated posts have been burned in a paddock, stock should be kept out until the remnants have been removed or buried. The salty contaminated ash may attract animals, and be fatal if consumed.
CCA-treated timber is not recommended for bee boxes. Studies in the United States found bees picked up trace amounts of arsenic to their detriment.
Although the risks are small, using treated wood in applications involving repeated contact with food - such as cutting boards and food boxes - is not recommended. A Swedish study found no contamination in potatoes, when peeled, after 7 months' storage in CCA-treated pine boxes, even though all the potatoes had been in contact with the wood surface. The peel of only two potatoes showed slight contamination (10).
Collecting rainwater from a roof with CCA-treated shingles for drinking is also not recommended. A two-year Canadian study found a slight rise in arsenic levels in rainwater collected off CCA-treated shakes in the first year, peaking at 5 months, and no detectable contamination in the second year (11).
Timber sale yards should have brochures available that set out safety precautions, which should always be followed. Standard safety equipment should be used whenever working with wood - treated or untreated. Absorption of arsenic through the skin is negligible (12). Nevertheless, gloves should be worn, to avoid splinters, and so that any sawdust or dislodgeable arsenic collecting on the gloves can be easily removed with the gloves before eating or smoking. As a precaution, the hands and face should still be washed before eating and smoking, and food and drink should never be left where sawdust can settle. A dust mask should be worn when sawing, machining or sanding, and cuts and abrasions protected from sawdust. Goggles should be worn when sanding, and during sawing or machining if there is any risk to the eyes from flying particles. If possible, sanding should be performed in a well-ventilated area. Overalls as well as gloves are recommended in high-dust situations.
Painting sawn CCA-treated timber has long been recommended as a way of reducing warping and checking, and will also reduce dislodgeable arsenic from the timber surface. Oils, stains and clear finishes are often not particularly durable coatings, so that arsenic may still dislodge from the coated timbers. The more durable exterior coloured (opaque) paints reduce levels of dislodgeable arsenic more significantly (13), (14).
None of the elements of CCA should move from logs into the dry indoor environment of a CCA-treated log house. However, some wood fibres may dislodge over time. These can be swept up or vacuumed, but if this sends dust into the air a dust mask should be worn. Indoor painting will seal and bind most loose surface fibres.
Particular caution is needed if fighting a fire in CCA-treated timber, because of the arsine gas liberated. Breathing apparatus may be required. CCA-treated timber tends to smoulder longer than untreated timber, a feature called 'afterglow'.
Currently, small volumes of CCA-treated timber wastes or off-cuts from domestic or residential uses should be disposed of through normal waste collection services. Trade or industrial users with large quantities of treated wood waste (more than 0.5 tonnes per month) may require additional approvals; check with local and state authorities in these cases. Sometimes it will be possible to reuse treated wood in another application.
CCA-treated timber must not be burned in barbeques, fireplaces or wood-burning stoves, or in any confined space, as toxic fumes and residues will be produced.
An important question, following the APVMA decision to restrict CCA for certain uses, is whether to retain existing CCA-treated timber structures, especially playgrounds. Ultimately, this will be an individual's or organisation's decision. Credible research to date suggests that arsenic ingestion from handling CCA-treated timber occurs at well below tolerable levels, if the precautions mentioned above are followed. The reader therefore needs to make their own informed decisions, and not necessarily believe alarmist claims. Note that the USA EPA in its announcement to restrict CCA stated: 'EPA has not concluded that CCA-treated wood poses unreasonable risks to the public for existing CCA-treated wood being used around or near their homes or from wood that remains available in stores. EPA does not believe there is any reason to remove or replace CCA-treated structures, including decks or playground equipment. EPA is not recommending that existing structures or surrounding soils be removed or replaced.' Similar statements in Australia can be found from EnHealth Council (15) and Better Health Victoria (16).
One study by Ensis in some local kindergartens found that playground equipment would not pose a health risk due to arsenic (17). This suggestion was further supported by a comprehensive study in Canada of dislodgeable arsenic levels on the hands of children, which were lower than anticipated in the APVMA review (18).
CCA-treated timber is safe to use, so long as all safety precautions are followed. Evidence of health problems associated with this use has not been proven. Because arsenic at higher levels is a carcinogen, and alternative wood preservatives are available, restrictions in some domestic applications will occur as a precaution. Problems can arise if warnings are not heeded and timber is misused or burnt. The difficulties of recycling CCA-treated timber and disposing of waste are significant drawbacks for the preservative, and the subject of current scientific research.
These are available, but are not yet widely used because wood treated with them is generally more expensive than CCA-treated timber. They combine copper and organic preservatives, and are more environmentally friendly as they do not contain chromium or arsenic. One alternative, ACQ (alkaline copper quat), is currently registered for use in all hazard classes except H6 (marine use). Tanalith E (copper azole) covers hazard classes H1 to H4, and H5 in softwoods (e.g. decking and posts). Both have been extensively tested, and generally perform as well as CCA. Remember to use hot-dip galvanised or stainless steel nails/screws when fixing these treated timbers. Other preservatives suitable for out-of-ground-contact uses include a number of light organic solvent preservative (LOSP) formulations.
If greater use were made of such alternatives, their price could be expected to fall. A concern with restricting CCA is that treated timber prices will rise and consumers will turn to more environmentally harmful materials such as aluminium, steel and concrete. These are not renewable, and greenhouse gases are generated in large quantities during their manufacture.
Ensis has a comprehensive development and testing program in wood protection technology. Indeed, copper ethanolamine nonanoate (CEN) was invented by Ensis (CSIRO) in the late 1970's (19) (20), and is a precursor to some of the current alternatives (copper ethanolamine quat = ACQ). Ensis helps industry and preservative suppliers by testing new wood preservatives and formulations according to established criteria for obtaining APVMA approval and recognition under Australian Standards. In addition, Ensis is investigating accelerated test methodology so that potential alternatives can be evaluated more rapidly.
* 1. Read, D. (2003). Report on copper, chromium and arsenic (CCA) treated timber. Environmental Risk Management Authority (ERMA).
* 2. Australian Standard 1604.1-2005. Specification for preservative treatment. Part 1: Sawn and round timber. Standards Australia, Sydney.
* 3. Cookson, L.J. (2001). Do we need the A in the CCA? 27th Forest Prod. Res. Conf., Clayton, Pp 8-9.
* 4. Peoples, SA. (1976). The amount and valence of arsenic excreted in the urine of dogs fed CCA-C in their diet. University of California, Davis, CA.
* 5. Harrison, D.L. (1959). Chemically preserved fence posts are harmless to stock. New Zealand J. of Agriculture 98: 293-294.
* 6. Ohlson C-G, Andersen A, Evans, FG, Karlehagen S and K. Nilsson (1995). Cancer incidence among CCA exposed workers in the wood preserving industry. In: Proceedings of the 3rd International Wood Preservation Symposium - The Challenge - Safety and Environment. International Research Group on Wood Preservation 1995, Document IRG/WP 95-50040-9, 147-149.
* 7. Szafraniec T (1991). CCA exposure in timber workers. J. Occupational Health and Safety: Australia and New Zealand. 7: 401-407.
* 8. Levi, M.P., Huisingh, D. and W.B. Nesbit (1974). Uptake by grape plants of preservatives from pressure-treated posts not detected. Forest Products J. 24: 97-98.
* 9. Speir, T.W., August, J.A. and C.W. Feltham (1992). Assessment of the feasibility of using CCA (copper, chromium and arsenic) - treated and boric acid - treated sawdust as soil amendments. Plant and Soil 142: 235-248.
* 10. Jorhem, L. and K. Nilsson (1991). Storage of potatoes in impregnated wooden bins. Swedish Wood Preservation Institute, Report No. 165.
* 11. Cserjesi, A.J. (1976). Permanence of preservatives in treated experimental shake roofs. Forest Products J. 26(12): 34-39.
* 12. Wester, R.C., Hui, X., Barbadillo, S., Maibach, H.I., Lowney, Y.W., Schoof, R.A., Holm, S.E. and Ruby, M.V. (2004). In Vivo percutaneous absorption of arsenic from water and CCA-treated wood residue. Toxicological Science 79: 287-295.
* 13. Lebow, S., Foster, D. and Lebow, P. (2004). Rate of CCA leaching from commercially treated decking. Forest Products J. 54: 81-88.
* 14. Stilwell, D.E. and Musante, C.L. (2004). Effect of coatings on CCA leaching from wood in a soil environment. In pre-conference proceedings, Environmental impacts of preservative-treated wood. Florida Center for Solid and Hazardous Waste Management, Gainesville, Florida, pp 113-123.
* 15. EnHealth (2005). EnHealth Council position on copper chrome arsenate (CCA) treated timber products.
* 16. Better Health (2005). Copper chrome arsenic (CCA) treated timber.
* 17. Cookson, L.J. (2005). Arsenic content of soil and wood chip fines in three kindergartens. Ensis Technical Report No. 151, 16 pp.
* 18. Kwon, E., Zhang, H., Wang, Z., Jhangri, G., La, X., Fok, N., Gabos, S., Li X-F. and :Le X. (2004). Arsenic on the hands of children after playing in playgrounds. Environmental Health Perspectives 112: 1375-1380.
* 19. McCarthy, D.F. (1978). Ethanolamine et al based wood preservative composition. Australian Patent Appl. No. 35221/78.
* 20. Greaves, H., Adams, N. and D.F. McCarthy (1982). Studies of preservative treatments for hardwoods in ground contact. 1. Penetration of cell walls by formulations containing copper. Holzforschung 36: 225-231.
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Last updated: 14 July 2006
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