The facts about CCA-treated timber

  1. Restrictions and regulations
  2. Treatment and fixation
  3. Leaching
  4. Animal contact
  5. Working with treated wood
  6. Disposal of treated wood
  7. CCA safety overview

Leaching

Page 3 of 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 cucumbers. 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 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.

  1. Read D. 2003. Report on Copper Chromium and Arsenic(CCA) Treated Timber  [external link, pdf] 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 LJ. 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 DL. 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, Nilsson K. 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 MP, Huisingh D, Nesbit WB. 1974. Uptake by grape plants of preservatives from pressure-treated posts not detected. Forest Products J. 24: 97-98.
  9. Speir TW, August JA, Feltham CW. 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 AJ. 1976. Permanence of preservatives in treated experimental shake roofs. Forest Products J. 26(12): 34-39.
  12. Wester RC, Hui X, Barbadillo S, Maibach HI, Lowney YW, Schoof RA, Holm SE, Ruby MV. 2004. In Vivo percutaneous absorption of arsenic from water and CCA-treated wood residue. Toxicological Science 79: 287-295.
  13. Lebow S, Foster D, Lebow P. 2004. Rate of CCA leaching from commercially treated decking. Forest Products J. 54: 81-88.
  14. Stilwell DE and Musante CL. 2004. Effect of Coatings on CCA Leaching From Wood in a Soil Environment  [external link, pdf]. In: pre-conference proceedings, Environmental impacts of preservative-treated wood. Florida Center for Solid and Hazardous Waste Management, Gainesville, Florida, pp 113-123.
  16. Better Health. 2005. Copper chrome arsenic (CCA) treated timber [external link]
  17. Cookson LJ. 2005. Arsenic content of soil and wood chip fines in three kindergartens [external link, pdf] Ensis Technical Report No. 151, 16 pp.
  18. Kwon E, Zhang H, Wang Z, Jhangri G, La X, Fok N, Gabos S, Li XF, Le X. 2004. Arsenic on the hands of children after playing in playgrounds. Environmental Health Perspectives 112: 1375-1380.
  19. McCarthy DF. 1978. Ethanolamine et al based wood preservative composition. Australian Patent Appl. No. 35221/78.
  20. Greaves H, Adams N, McCarthy DF. 1982. Studies of preservative treatments for hardwoods in ground contact. 1. Penetration of cell walls by formulations containing copper. Holzforschung 36: 225-231.