Fig. 2. An illustration of (A) macroscopic-level and (B) molecular-level data. Macroscopic data has yielded a multitude of indirect hypotheses which are now being refined with the application of direct, molecular-level observations. Macroscopic methods commonly employ batch equilibration experiments that produce sorption isotherms (note: not all sorption isotherms are nonlinear; linearity varies with sorbate and sorbent properties and the type of mechanisms that are dominating the attenuation process). Molecular-level studies enable sorption mechanisms, such as those between trifluralin and SOM (adapted from Simpson et al., 2001). Two-dimensional molecular-level data, such as correlation spectroscopy NMR of a soil humic acid, displayed from Simpson et al. (2004), can provide detailed structural information about humic material and can be used to decipher specific SOM interactions with contaminants. Reprinted with permission from Simpson et al. (2004). Copyright (2004) Environmental Toxicology and Chemistry, Alliance Communications Group.