The pollution of terrestrial ecosystems is reflected by the structural characteristics of the humic substances they contain. We studied the thermal behaviour of humic substances (fulvic acids and humic acids) from differently polluted soils in an attempt to identify possible links to structural changes in the substances. Using a coupled analysis technique comprising thermogravimetry/Fourier transform infrared spectroscopy and multivariate data analysis, correlations with elemental composition were calculated and classifications with model classes ascertained. The findings showed that stress situations in soils are reflected in the thermal characteristics of the humic acid fractions.