Fungal degradation patterns and toxicity of furfurylated wood
Sammanfattning: The demand for timber products is increasing with global population and affluence. Concerns regarding conventionally used toxic wood preservatives and the deforestation of tropical forests have become more prominent both socially and politically. Wood based products are generally recognised as an environmentally favourable raw material. New and innovative wood products with extended service life can be expected to contribute to increased carbon dioxide (CO2) storage. Modified wood is an environmentally benign alternative to traditional preservative treated wood. Some examples of wood modifications are thermal modification, acetylation, furfurylation and modification with DMDHEU (dimethylol dihydroxy ethylene urea). Currently little is known about the mode of action of modified wood and the optimisation of these can only be accomplished fully when knowing how the modification affects the microbial decay mechanisms. The present study showed that the conditions of the furfurylation process are decisive for the outcome of the toxicity analysis of leaching water from furfurylated wood. It is likely that the intermediate vacuum drying step leads to a decrease in toxicity towards the two aquatic organisms Vibrio fischeri and Daphnia magna. The reason for this could be that the intermediate vacuum drying step provides a more efficient polymerisation of the furfuryl alcohol molecule. This could also explain why higher weight percent gain (WPG) does not automatically lead to higher toxicity. The present study also shows that a furfurylation treatment, with a WPG lower than 25, seems unable to protect the wood completely against wood deterioration organisms. The results might also indicate an inability of the fungus Trametes versicolor to utilise the furfuryl alcohol polymer as a nutrition source, but this needs to be further investigated. In general, the fungal deoxyribonucleic acid (DNA) content, measured with quantitative real-time polymerase chain reaction (qPCR), and visual rating (according to the standard EN 252) correspond well. However, whereas the qPCR measures the Basidiomycota DNA content inside the wood indicating internal degradation, the EN 252 rating is based on evaluation of the surface layer of the wood. In many cases there may be a rather extensive mycelia mass on the wood surface which is not necessarily affecting the strength capacity. Further studies need to be conducted to optimise existing methods and develop new methods to detect and quantify deteriorating organisms before the onset of any significant loss of strength. More knowledge needs to be gathered about the complex decay mechanisms in treated wood in order to optimise protection.
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