Characterization of contaminated soils using confocal laser scanning microscopy and cryogenic-scanning electron microscopy

The distribution of nonaqueous phase liquid (NAPL) contaminants in the micr ostructure of soil was examined by microscopy. The fluorescence of contamin ant polynuclear aromatic hydrocarbons allowed imaging of soil aggregates us ing fluorescent confocal laser scanning microscopy (CLSM). Cryogenic scanni ng electron microscopy was then used to examine samples at higher magnifica tion. The results indicate that the NAPL covers the surface of aggregates a nd fills the accessible interaggregate pores of diameter 0.05-5 mu m, creat ing 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.