Differences in quinone redox system of humic substances between endemic and disease-free areas in Kashin–Beck disease-affected Changdu Region, Tibet, China

Kashin–Beck disease (KBD) is an endemic disease in China with the highest incidence rate in Tibet region. Promoted generation of oxygen free radicals by semiquinone structure of humic substance (HS) in drinking water was considered to be one of its pathogeneses. Therefore, detailed analysis of HS was performed in water and sediment samples collected from three endemic and three disease-free areas in Changdu Region, Tibet, China. After purification of the HS in the samples, the fractions of HS were characterized using electron paramagnetic resonance, 13 C nuclear magnetic resonance, fluorescence spectroscopy with parallel factor analysis and Fourier transform infrared spectroscopy (FTIR). The organic carbon content of HS did not show a significant difference between endemic and disease-free areas or correlation with KBD-associated morbidity. Except FTIR, all techniques succeeded in characterization of the quinone redox system, indicating their validity and consistency. The quinone redox system in aquatic HS exhibited significantly higher level of the following indexes in endemic areas than disease-free areas: semiquinone radical content of fulvic acid (FA) ( p