Influence of fungal exposure on the redistribution of copper in treated spruce wood
M Humar, F Pohleven, R J Murphy, D J Dickinson, I Moris, M Zupancic, P Kalan, M Petric
The redistribution of copper in treated wood after exposure to basidiomycete decay fungi is described. The micro-distribution of copper in copper(II) sulphate or copper(II) octanoate/ethanolamine treated Norway spruce wood before and after exposure to 3 different wood decay fungi was studied using transmission electron microscopy with X-ray microanalysis. The copper content of the mycelium and the nutrient medium was also determined by atomic absorption spectroscopy. Finally, light microscopic analyses of decayed samples was performed. Both copper-tolerant (Antrodia vaillantii) and copper-sensitive fungi (Trametes versicolor and Gloeophyllum trabeum) changed the distribution of copper in the treated wood after 16 weeks of exposure. The redistribution of copper in copper sulphate treated samples exposed to tolerant A. vaillantii was characterised by the excretion of oxalic acid and formation of copper oxalate in the cell lumens, on the surface of treated wood blocks and on the fungal hyphae. In the presence of ethanolamine, the formation of copper oxalate by A. vaillantii did not occur but instead diffusion of copper into regions of lower copper
concentration (centre of the blocks and nutrient medium) took place. This type of redistribution/diffusion of copper was also observed when treated wood specimens were exposed to the copper-sensitive fungi.