UV photoinitiated changes of humic fluorophores, influence of metal ions

Fluorophore types and their photochemical stability have been tested in two samples of humic acids (HA) and four types of fulvic acids (FA) extracted from upper soil horizons (O and A horizons) in Norway spruce forest mountain ecosystems. Only one type of fluorophore occurred in all samples, with an excitation maximum at 310 nm for both HA and FA samples and emission maxima between 420-435 and 440-450 for HA and FA, respectively. HA weak native fluorescence increased significantly during irradiation in the first 12 h. Fluorophores in FA were uniformly degraded from the beginning of irradiation. Addition of metal (aluminium or ferric) ions did not affect the positions of fluorescence maxima in any of the studied samples; mild effects on fluorescence intensities were observed.