LASER-INDUCED FLUORESCENCE OF MARINE SEDIMENTARY INTERSTITIAL DISSOLVED ORGANIC-MATTER

Flourescence spectroscopy is investigated on dissolved organic matter (DOM) of marine sedimentary interstitial waters (IW). These were colle cted near urban outfalls and a river month in the Mediterranean, havin g a high interstitial dissolved organic carbon content (DOC). A self-m ade experimental laser-crystal fluorimeter and two classical spectrofl uorimeters are employed (Perkin Elmer LS-2 and LS-50). For an excitati on wavelength at 366 nm, a definite emission ''bump'' is found for LS- 2 and LS-50, which is caused by specific fluorophores. Two kinds of cu rves are reported with the experimental laser, the ''laser induced flu orescence'' produced at a fixed time (LIF) and the ''time resolved emi ssion spectra'' (TRES), which are three dimensional space graphs. Phot ochemical decay of fluorescent organic matter (FOM) results in an almo st exponential decrease of the complete LIF spectrum. A correlation ex ists between two peaks of the spectra, the broad band around 475 nm an d the narrow peak at 720 nm, depending on DOC. The emission spectra (E FS, LIF, TRES) are systematically compared with three different factor s, being filtration, pH and added aluminium ion. (1) filtration affect s the fluorescence of organic matter by minimizing the scattering inte rference. (2) pH affects the ''fine structure'' of the broad band arou nd 475 nm. As concerning the increase at 530 nm at stronger pH, one ca n consider that there is a competition between H+ ion and other cation ic species: the anionic form favors the formation of chelate species. This is due to stereostructural changes of FOM, involving neutral, ani onic or chelate species. (3) Aluminium enhances fluorecence intensitie s near 530 nm, which is attributed to a colloidal organo-aluminium com plex formation. Additions of Al3+ in excess, at constant salinity, res ult in essential modifications of the equilibrium between spheroidal a nd unfolded geometries of FOM. Since a decreasing intensity of this '' bump'' at 530 nm is observed after re-filtration, this confirms the po ssible colloidal state of the Al-FOM complex. Emission fluorescent spe ctra (EFS) obtained by LS-2 due to Al3+ addition, at natural pH and na tural salinity, are treated with a linear regression method; an appare nt stability constant is calculated at 530 nm, K = 3.58.