Environmental nanoparticles found in soil systems and biosolid materials may pose a considerable risk to groundwater quality as potential contaminant carriers. Currently, little information exists about the stability and contaminant transport behavior of soil nanocolloids in natural environments. This study involved physical, chemical, and mineralogical characterizations of nanocolloids (< 100 nm) and macrocolloids (100-2000 nm) fractionated from three Kentucky soils and one biosolid waste material. Particle morphology and size distribution were investigated with scanning/transmission electron microscopy and dynamic light scattering. Electrophoretic mobility was determined with phase angle light scattering (PALS) and the zeta potential was estimated using the Hückel approximation. Mineralogical composition was determined by x-ray diffraction and thermogravimetric analyses. Sorption affinities of nanocolloids and macro-colloids for Cu2+, Pb2+, AsO3-, and SeO4-2 contaminants were assessed by adsorption isotherms, while stability characteristics of their suspensions at different pH levels and ionic strengths were determined with settling kinetics experiments. Comparisons of nanocolloid and macrocolloid particles suggested significant differences in morphology, mobility and reactivity implicating a diverse potential for contaminant transport behavior between and within the nano- and the macro-particle size range.