Popular Science: What to do with toxic wood? Let’s compost it!
Creosote is a compound made from coal tar, used for the treatment of railroad sleepers, electricity poles or wooden structures of bridges to prevent them from rotting. Since it was found that it is carcinogenic, its use in the EU has been prohibited. The disadvantage of such treated wood is that it contaminates the surrounding soil layers and ground waters. Currently, it is most commonly disposed of by incineration or landfilling; however, it appears that composting is a valuable and environmentally friendly alternative.
There are numerous studies that dealt with biological removal of polycyclic aromatic hydrocarbons (PAH), where creosote also belongs. However, the information about the overall composition of biological communities that are involved in the process of bioremediation was still lacking. A technique called next-generation sequencing (NGS), which has been previously used very rarely in studies of this type, can very well serve this purpose. Thanks to this tool, it is possible to explore microbial communities, including the compost community in this case, in detail.
Scientists have tested composting creosote-treated wood with two substrates – grass cuttings and broiler litter. Such co-composting has proved to be a feasible and very efficient procedure for decontamination and detoxification of wood. Grass cuttings have proved to be a preferable bulking agent, because it supported faster and more efficient removal of toxic hydrocarbons. Regarding the composition of microbial communities, it changed very quickly in both cases. In total, scientists identified 2,544 bacterial and 169 fungal unique sequences. Some of the recorded organisms have been previously described as capable to degrade PAHs. Degradation occurred most intensely in the green compost at high temperatures. Key players proved to be gram-positive bacteria (Bacillus and Actinobacteria) and yeasts that predominated in the community over other bacteria and fungi. But so far it is still unclear which specific role they play in decomposing of organic matter and pollutants. This question could be answered by further research using for example PAH compounds with labeled carbon isotopes 13C and 14C.
Covina, S., Fabianová, T., Křesinová, Z., Čvančarová, M. Burianová, E., Filipová, A. Voříšková, J. Baldrian, P. Cajthaml, T. (2016): Polycyclic aromatic hydrocarbons degradation and microbial community shifts During co-composting of creosote-treated wood. Journal of Hazardous Materials 301: 17 to 26.