Chemotaxonomic Species and Origin Identification of Wood in Pulp and Paper

Abstract

This work presents the development and proof of concept of a novel chemical method for wood taxa and origin identification in pulp and paper. In order to conserve nature and halt the ongoing and severe crossings of planetary boundaries such as land-system change and biosphere integrity, it is essential to combat deforestation and the loss of genetic diversity within global forests. Therefore, a variety of national and international laws have been enacted with the objective of protecting the environment. However, there is a need for science-based monitoring tools to ensure that these laws are effectively enforced in practice. The method is based on the differentiation of wood extract profiles that remain in pulp (chemotaxonomic fingerprinting) and involves cryo-ball mill grinding and Soxtherm extraction of bleached pulp or paper samples with n-hexane, followed by thermodesorption of the dried extracts and gas chromatography - mass spectrometry (TD-GC-MS) analysis. The generated chromatograms undergo a series of pre-processing steps, including ion filtering, smoothing and peak deconvolution and are then added to the reference database (DB). The investigation of optimal configuration settings for the DB was also part of this work. The subsequent identification of samples of unknown composition is conducted through querying against the DB on three comparison parameters: marker peak scores (MPS), reverse similarity index (RSI), and matched chromatogram area (MCA). The methodology has been validated on different measuring devices. However, there is currently a partial dependence of the database query results on the measuring system. Furthermore, the novel extractant-based approach was evaluated in an independent external blind test and compared to the established anatomical identification method. The blind test comprised 38 exemplary species of mainly tropical hardwood, which were processed in unknown mixtures into 15 test sheets and provided to four participating institutes for analysis. The results demonstrate that the new chemotaxonomic method yielded outcomes that were comparable to those obtained through the morphological-anatomical method, which is currently employed for all assessments. However, both approaches show distinct strengths and weaknesses in the recognition of individual wood taxa, suggesting that a combination of both methods could potentially enhance the overall hit rate. Another study included in this work successfully differentiated the origins of the wood genera Gonystylus and Rubroshorea and the wood species Tectona grandis in fully bleached pulps. Certain compounds responsible for the differentiation of specific geographical origins were found for every taxon. The results of the origin differentiation could be particularly useful for the verification of harvest origin declarations at border crossings of pulp and paper products, as well as for the enforcement of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Currently, this is the only method available for this purpose. A variety of optimisation possibilities of the chemotaxonomic database approach are discussed, including sample preparation techniques such as advanced tuning of the GC-MS instruments used, data processing methods such as ion filter settings and database configuration. The outlook section outlines future prospects for further method validation on industrial samples and the potential use of machine learning for automation.