Characterization of humic substances in highly polluted river sediments bypyrolysis methylation-gas chromatography-mass spectrometry

Humic substances were extracted from two sediment cores sampled in a river on the outskirts of a large city (Deule near Lille, France) and in its high ly polluted oxbow-lake. Humic acids (HA) were characterized by infrared spe ctroscopy and in situ pyrolysis/methylation-gas chromatography-mass spectro metry. The main results are the substantial aliphaticity of HA in the oxbow -lake at all depths, mainly due to the presence of a lipid fraction associa ted with the HA structure. The abundance of sterols in this fraction implie s that lipids could originate from the accumulation of sewage in the oxbow- lake. Humic acids of the Deule sediments show a different trend; their evol ution is characterized by a decrease of the pollutant inputs with increasin g depth. The results demonstrate the efficiency of Py-GC-MS in identifying the different organic contributions to HA and in distinguishing natural fro m anthropogenic sources. (C) 2001 Elsevier Science Ltd. All rights reserved .