Fungal bioremediation of copper, chromium and boron treated wood as studied by electron paramagnetic resonance

In future years, problems concerning the disposal of waste copper/chromium-treated wood will increase significantly. One of the environmentally friendly options of dealing with such treated wood is through bioremediation with copper-tolerant wood decay fungi in order to recycle both the wood fibers and the heavy metals. To study changes during the bioremediation process, Norway spruce (Picea abies) samples were vacuum impregnated with 5% CCB solution. Some samples were also impregnated with copper or chromium solution of the same concentration as in the CCB preservative. Following conditioning of the samples, they were then exposed to two copper-tolerant brown rot fungi, (Antrodia vaillantii, Leucogyrophana pinastri) and two copper-sensitive brown rot fungi, (Gloeophyllum trabeum, Poria monticola) for a period of 4–8 weeks. After exposure, the samples were cleaned of the mycelia and leached with water or 1.25% ammonia solution for 4 days. The concentrations of Cr and Cu in the leachates were determined. After the leaching process, the samples were studied using electron paramagnetic resonance (EPR). The results obtained showed the important role oxalic acid produced by the decay fungi plays during leaching of the metals from the treated wood. Furthermore, it was also found that though excretion of oxalic acid is necessary for the leaching of metals, it does not fully explain fungal ability to decay copper preserved wood.