Analytical Sciences

Abstract − Analytical Sciences, 37(7), 977 (2021).

Biodegradation and Structural Modification of Humic Acids in a Compost Induced by Fertilization with Steelmaking Slag under Coastal Seawater, as Detected by TMAH-py-GC/MS, EEM and HPSEC Analyses
Hisanori IWAI,*1 Mitsuo YAMAMOTO,*2 Motoyuki MATSUO,*3 Dan LIU,*4 and Masami FUKUSHIMA*5
*1 Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, 24 O, Wake, Nomi, Ishikawa 923-1224, Japan
*2 Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan
*3 Department of Multidisciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
*4 Department of Creative Engineering, National Institute of Technology, Ariake College, 150 Higashihagiomachi, Omuta, Fukuoka 836-8585, Japan
*5 Division of Sustainable Resources Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
The compost’s humic acid (HA) content decreased when it was fertilized in coastal seawater with steelmaking slag, as confirmed. This study clarified the cause for this change by a detailed analysis of the structural changes in HAs based on the TMAH-py-GC/MS, HPSEC, and 3D-EEM spectra. An increase in the levels of pyrolysates of tannic acid with a low polymerization degree was attributed to the biodegradation of a high polymerized aromatic structure. Moreover, analyses of 3D-EEM, supported by HPSEC, indicated that approximately 20 kDa of the fluorescent matter was generated at the protein-like peaks (Ex/Em = 220/340 and 275/350 nm) in HAs derived from a mixture of compost with steelmaking slag. It would be caused due to the formation of HAs from the bacterial by-product by a catalytic reaction of the steelmaking slag. From these findings reported herein, we conclude that bio-degradation was a major reason for the decreased HA content, and the formation of HA from a part of the degradation products. This would be a reason for the structural modification of HA under the seawater condition.