I am concerned to hear that CCA treated timber has been used to construct garden beds and other structures in some school gardens, so it might be a good time to remind readers that the uses of these timbers have been restricted.
Since the end of March 2006, timber treated with copper, chromium and arsenic as a preservative (CCA timber) is not permitted to be used for garden furniture, picnic tables, exterior seating, children’s play equipment, patio and domestic decking, or handrails.
Problems with CCA treated timber
The restrictions on use were implemented by the Australian Pesticides and Veterinary Medicines Authority (APVMA) because they were “not satisfied that the continuing use of CCA for timber used in structures with which the public (and particularly children) are likely to come into frequent and intimate contact is safe“.
Common sense would dictate that the APVMA restrictions would also apply to garden beds (as they do to sand pits) because this timber can leach arsenic (a known carcinogen) into compost and soil for up to 20 years, and some species of food crops can absorb high levels of arsenic.
As young children have a tendency to put their fingers in their mouths, and tend to be less careful about washing their hands, they can ingest significant amounts of leached arsenic, a known carcinogen, from CCA treated timber. Children are, of course, more vulnerable to all pesticides because their organs are still developing and young children eat more food per kilogram of body weight than adults do.
The APVMA’s decision follows the phase-out for domestic uses of CCA treated timber in the US, EU, Canada, Indonesia and Vietnam, and restrictions to its use in Japan.
The regulations allow the use of CCA treated timber for ‘structural timbers’ and the timber industry has included retaining walls in that description. However, the APVMA Review (page 11) clearly states, structural timbers “where frequent contact is unlikely, and the level of exposure and risk, is low“.
Once installed ……..
Research by the US EPA (in 2005) found that penetrating sealants can reduce, but not eliminate, arsenic migrating from the treated wood. The data show sealants that can penetrate wood surfaces are preferable to products such as paint, because paints and other film-formers can chip or flake, requiring scraping or sanding for removal, which can increase exposure to arsenic.
More recent US research has found that arsenic levels on CCA-treated wood remained high for 20 years, and that timber had to be re-coated every 6 months, making the maintenance of this timber to reduce students’ exposure a tedious and expensive process. The only safe solution is to replace the CCA treated timber with one of the safer alternatives that are now available.