Ultraweak chemiluminescence from γ-irradiated humic acids

Humic substances, i.e. dark paramagnetic polymeric anionic polyelectrolytes, belong to the most widespread macromolecular substances of biogenic origin in soil and aquatic environments. The exact structure of humic substances is unknown because of their complexity resulting from unrecurring precursors, from their composition and their process of synthesis. Degradation processes of these substances can be a source of energy, carbon and nitrogen for soil and aquatic microorganisms. CO2 released in the degradation processes contributes significantly to the greenhouse effect [3]. Humic substances effectively absorb non-ionizing radiation, such as ultraviolet (UV), visible or infrared radiation. Much less is known about their sensitivity to ionizing radiation, such as γor X-rays. They exhibit a permanent “dark” paramagnetism (10−10 spin/g), photoinduced transient electron paramagnetic resonance (EPR) signals, probably originating from redox semiquinone moieties [3]. Therefore, humic substances are an efficient target for solar radiation and most probably for ionizing radiation. Up to now, only few papers are available on the possible interaction of humic substances with ionizing radiation [4, 8], as compared to those dealing with the effect of UV [5, 8, 11]. The only substances, which have the elemental composition, molecular weight and physicochemical properties similar to humic substances, are melanins. Although their interaction with ionizing radiation is of high medical relevance [6], the possible secondary chemilumiscence induced by γor X-rays has not yet been investigated. Earlier studies were Ultraweak chemiluminescence from γ-irradiated humic acids Wieslaw Goraczko, Janusz Slawinski