Application of pyrolysis-gas chromatography-mass spectrometry to the characterization of humic substances resulting from decay of aquatic plants in sediments and waters

Pyrolysis-GC-MS, elemental analysis and i.r. spectroscopy reveal major differences between humic substances from aquatic plants (algae and aquatic phanerogams) and lagoonal, marine and lacustrine deposits. Algae are enriched in proteins and their pyrolysis yields numerous nitrogenous by-products (alkylpyrroles, nitriles and alkylpyridines) along with aromatic compounds which are thought to reflect the decomposition of individual amino-acids (styrene, toluene, phenol and p-cresol). These compounds are less abundant in the pyrolysis products of humic substances from phanerogams with increasing amounts of methoxyphenols, characteristics of lignins.In the deposits of the Kerguelen Islands and of a “blue lake” in Greenland, the importance of algal populations is emphasized by pyrolysis products corresponding to nitrogenous and carbohydrate derivatives. Phenols and cresols in the pyrochromatograms of these samples are interpreted as evidence of polypeptides rather that lignin: p-cresol is much more abundant than the other cresols, suggesting the formation of phenols by way of tyrosine.Lagoonal sediments, in contrast, seem typical of intermixed development of algae and phanerogams.Differences between fulvic and humic acids are emphasized by the development of polyphenols and protein derivatives in humic acids compared to polysaccharide derivatives in fulvic acids. Other constituents revealed by PY-GC-MS include N-acetyl aminosugars, phthalates and aliphatic compounds.