Mobile colloids in soils and aquifers can act as carriers for adsorbed contaminants and thereby facilitate the transport of contaminants. In order to understand the problem, colloids isolated from soil were used as adsorbents for toxic metals such as Pb(II), Ni(II), Cu(II), Cr(VI) and dyes such as alizarin red and methylene blue. Column experiments were conducted to investigate the mobilization of in situ colloids from soil and their size distribution. Experiments were also conducted to study the transport of alizarin red dye through soil columns at different ionic strengths (0.01 and 0.001 M) and pH (pH 7.5, 9.5 and 11.5) and toxic metals at the ionic strength of 0.001 M. The colloids showed significant adsorption toward the contaminants with the adsorption of methylene blue reaching as high as 625 mg g−1. The mobilized colloids had significant difference in their size distribution, and the cumulative mass curve of colloids followed a nonlinear pattern in contrast to the previously reported linear behavior on model systems. The dye and toxic metal transport experiments suggested their sensitivity to low ionic strength influent solution, with the capacity of colloids to transport the dye and toxic metals increasing at low ionic strength and the transport of dye at high pH. With decreasing ionic strength, the release rate coefficient of dye increased. This study represents an important step to understand colloid-associated contaminant transport in natural soils.