Spin labeling EPR analyses of soil: A new method to investigate biogenic and abiogenic interactions of amines in the environment of natural soils

Abstract

A major focus of this paper is to investigate the environmental fate of chemical pollutants with the amine functionality in soils and its underlying molecular processes. Taking into account a key role of the amine in the structure of chemical pollutant and its reactivity, spin labels with different amine groups were applied to natural soils and investigated by means of electron paramagnetic resonance (EPR) analysis. As spin labels, stable nitroxide radicals modeled chemical pollutants with the amine and, meanwhile, afforded knowledge of the molecular environment of soil where they were located or bound via the amine. The first results of the Spin Labeling EPR investigation showed that chemical pollutants including the amine were differently partitioned among soil sites with the different water–octanol coefficients Kow in dependence on the amine base that allowed for accumulating the amines with a weak base by a non-hydrolysable part of soil organic matter, whereas the amines with a strong base were transformed or bound to small molecules (<5 kDa) of a hydrolysable part of soil organic matter. The uneven partitioning of the amines among soil sites of different hydrophobicity intensified a part of anoxic areas in soil that, in turn, resulted in a restriction of areas fit for soil aerobic microorganisms and a decrease in their magnitude.