BOOK OF ABSTRACTS 163 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Friday, 28 August 2026 / Hall C Travel Awardee Presentations TA2 Estimation of Black Carbon in a Humic Acid Inventory and Evaluation of an Alternative BPCA Methodology Maria Lorena Goretti Quinones1, Miyuki Kondo2, Yukiko Yanagi3, Masayuki Tani4, Morimaru Kida1, Takeshi Suzuki1, Nobuhide Fujitake1 1 Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan, lorena.goretti.q@gmail.com 2 National Institute for Environmental Studies, Japan 3 Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Japan 4 Research Center for Global Agromedicine, Obihiro University of Agriculture and Veterinary Medicine, Japan Humic acids (HAs) from black soils, such as Andosols and Chernozems, exhibit similar properties, including high aromatic carbon content and a high degree of humification, despite differing formation conditions. Although the causes of these similarities are not fully understood, they have been partially attributed to the presence of charred plant residues, such as black carbon (BC), as suggested by other authors [1,2]. Black carbon is a stable product of incomplete biomass combustion that can persist in soils over long periods and has gained increasing attention. However, the characterization of black carbon specifically within humic acids has received relatively little attention. Therefore, this study aimed to evaluate the contribution of BC to the composition of humic acids by comparing its content within a humic acid inventory. The BC content of 50 humic acid samples from diverse soils was estimated to assess its distribution and relationship with aromatic carbon. BC was quantified using the benzene poly-carboxylic acid (BPCA) method, which involves oxidation of aromatic structures followed by analysis of BPCA compounds, as described in previous studies [3]. Initially, quantification was performed using high-performance liquid chromatography (HPLC), and subsequently, a total organic carbon (TOC) analyzer was evaluated as a simplified alternative. The results showed that Chernozems and Andosols presented higher BC content (13–33% of total carbon, expressed as BC%) compared to forest soils (7–9 BC %). A positive relationship between BC and aromatic carbon was observed (r = 0.77, p < 0.05), indicating that HAs from most black soils with high aromaticity also contained elevated BC levels, supporting the contribution of charred residues to their composition. However, the distribution of individual BPCAs did not show a clear relationship with soil type, and no significant enrichment of highly substituted BPCAs (B5CA and B6CA) was observed in black soils, suggesting variability in BC structure. Comparison of analytical methods revealed a strong
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