Characterization of Contaminated Soils Using Confocal Laser Scanning Microscopy and Cryogenic-Scanning Electron Microscopy

Abstract

The distribution of nonaqueous phase liquid (NAPL) contaminants in the microstructure of soil was examined by microscopy. The fluorescence of contaminant polynuclear aromatic hydrocarbons allowed imaging of soil aggregates using fluorescent confocal laser scanning microscopy (CLSM). Cryogenic scanning electron microscopy was then used to examine samples at higher magnification. The results indicate that the NAPL covers the surface of aggregates and fills the accessible interaggregate pores of diameter 0.05−5 μm, creating a discrete phase inside the pores. The NAPL phase was highly associated with clay minerals. These physical observations suggest that diffusion of contaminants out of NAPL-clay structures and NAPL-filled pores is important in release of contaminants from soil.