Studies on marine humic substances I. Isolation of humic substances from seawater with an effective adsorbent, GDX-102 adsorption resin

Abstract

Apart from about 35 g/1 of inorganic salts seawater also contains a small amount of organic matter ranging 0.5--2.0 mg C/1. Dissolved organic matters (DOM) are the main component in total organic matter, and only I0~o of these DOM including sugars, amino acids, fatty acids etc. are identified~X~L By the estimate of Rashidtn3, however, humic substances constitute over 60---80 ~ of naturally occurring organic matter in seawater with the concentration of only 0.003--0.8 rag/1 11~. The humic substances in the ocean are mainly originated from phytoplankton, but in the coastal water the humie substances from land and benthic brown seaweed exudates are also mixed in them. Marine humic substances are extremely complex amorphous high molecular weight polymers, and are strongly reactive with many different metallic ions, affecting directly their speciation, concentration and equilibrium relation in seawater, as well as their precipitation and transfer in marine environment. In addition, the low molecular weight fractions of humic substances in seawater show a promoting effect on the growth of phytoplankton Es.ga. Thus, humic substances in seawater not only play an important role in the geochemical processes of metallic ions and organic matters, but also have an important ecological significance. The properties of humic substances from soils and coals have been studied for a long time, and a great deal of informations have been published te.ls~. But the investigation on humic substances from seawater, owing to their low concentration, only began in the early fifties by Wilson et al 1203, Jeffrey et al csl and Johnston et al 141 using active carbon as the adsorption medium. Afterwards Moed 171 and Williams et al txs3 recommended the use of inorganic adsorbents, but their adsorption efficiency was low. Since the latter part of the sixties Sieburth et alCXs~, Riley et al 1:23 and Stuermer et al t~6~ have tried to use nylon stocking and powder, and styrene-divinylbenzene polymer Amberlite XAD resins to extract humic substances from seawater. Amberlite XAD-2 was used with some success by Stuermer et al 1163, and recently XAD-7 and _8Ex3 were found to be much better than XAD-2 in isolating humic substances from bog and river waters. A comparative study of the adsorption e~ciency for humic substances from seawater