The growth and metal content of plants grown in soil contaminated by a copper/chrome/arsenic wood preservative
C Grant, A J Dobbs
Salts of copper, chromium and arsenic are used together in water soluble formulations for the preservation of wood against insect and fungal attack. Copper/chrome/arsenic (CCA) preservatives are of proven efficacy and, used correctly, ensure a useful service life for timber for 30 years or more with little, if any, attendant threat to the environment from the treated wood itself. The preservative treatment site can, however, provide a point of entry for the preservative into the general environment by way of spills and leaks of the treating fluid and run off from treated wood, with resultant contamination of the surrounding soil. The possible effects of the CCA salts on plant growth and metals uptake are the subject of this paper. In a series of greenhouse pot experiments the effects of varying concentrations of CCA in soil on the germination, growth and cropping of beans, carrots and tomatoes was studied. Crops produced by the plants were analysed for their copper, chromium and arsenic contents. Additionally, grasses were grown to assess possible land reclamation difficulties. It was found that soil having a combined copper, chromium and arsenic concentration of approximately 7000 ppm completely inhibited the growth of all the plants tested, while certain concentrations below this inhibited or retarded growth to some degree. Carrots grown in soil containing approximately 1000 ppm Cu, Cr, As (200 ppm As) produced crops containing nearly twice the current recommended limit for arsenic in food. Relating the levels of CCA used in the experimentally dosed soil with the amounts found in soil samples taken from preservative treatment sites, it is apparent that many contaminated areas would not support plant life. Less heavily contaminated soil will support growth and may give rise to crops with arsenic levels higher than those deemed to be safe.