Microscopic examinations of CCA-treated Pinus radiata timbers in industrial cooling towers in New Zealand showed bacteria and soft rot fungi to be primarily responsible for the decay of these timbers. Of these micro-organisms, erosion bacteria appeared to be most widespread, attacking wood cell walls independently as well as together with tunnelling bacteria and soft rot fungi. Tunnelling bacteria attacked wood often with soft rot fungi, and less commonly with erosion bacteria. Sampling of wood from different locations in the cooling towers inspected indicated erosion bacteria to be most tolerant of oxygen limiting conditions among the microorganisms which attacked the wood, as bacterial erosion was the only type of decay present in the wood constantly saturated with water. The evidence presented of the presence of widespread bacterial attacks of industrial cooling tower timbers in New Zealand is the basis for recognising bacterial importance in the deterioration of cooling tower timbers.

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