EXTRACTION OF CHROMOPHORIC HUMIC SUBSTANCES FROM SEAWATER

Chromophoric humic substances were extracted from seawater using hydrophobic solid-phase extraction, ultrafiltration, and a hydrophobic macroreticular resin (XAD-2). Four criteria were used to evaluate the efficiency of extraction: (1) UV-visible absorbance, (2) dissolved organic matter fluorescence, (3) capacity for photoproduction of H2O2, and (4) retention of total organic carbon. Extraction efficiencies for solid-phase media followed the order C18 > C8 > cyclohexyl (CH) > phenyl (PH)=C2. The extent of removal of humic substances from seawater decreased between 70 and 40% with volume extracted and varied with the source of water. Using our criteria, extraction of humic substances with C18 solid phase was between 22 and 84% more effective than with XAD-2. Concentration of humic substances by ultrafiltration was more efficient with membranes of molecular weight cut-off values of 500 than 5000. C18 solid-phase extraction of humic substances was as effective as ultrafiltration. Seawater reconstituted with humic substances extracted by C18 solid-phase extraction and by ultrafiltration had properties that were between 90 and 101% of those of the original water samples. Our results indicate that extraction of humic substances from seawater is most conveniently achieved by using C18 solid-phase extraction. A scaled-up version of this procedure has been used for the extraction of chromophoric humic substances from large volumes (1001) of coastal and open-ocean water. © 1990.