NUKLEONIKA 2004, 49(4):143-147

Dried humic acid and its aqueous solution in 0.1 M Na₂CO₃ were g-irradiated with 1-90 kGy from ⁶⁰Co. Thereafter, a secondary ultraweak radiation in the spectral range of l = 340-650 nm from aqueous solutions was recorded as long-lived chemiluminescence (CL). Only for absorbed doses lower than 10 kGy low intensity signals of the CL decay were measurable. For absorbed doses higher than 40 kGy residual flat and weak signals are observed. Humic acid irradiated in the dry form did not reveal statistically significant CL. Absorption spectra (l = 240-800 nm) of irradiated solutions indicated the occurrence of a dominant degradation process of the humic acid macromolecular components. The effect of H₂O₂ and CL enhancers (luminol and lucigenin) on the intensity and kinetics of CL proved the participation of reactive oxygen species and the free radical mechanism in the CL and degradation processes. The dose-effect relationship (i.e. g-radiation absorbed dose vs. intensity of g-radiation-induced CL) showes a non-linear shape, especially in the range of 1–10 kGy, which suggests complex radical mechanisms. A possible ecological significance of the observed phenomena is briefly discussed.