The significant probe dilution is one of the reasons to use soluble dyes and concentrated ion solutions for studies of colloid transport in subsoils and aquifers. We studied the clay transport in sand columns with Rhodamine 6G-intercalated montmorillonite (MMT). Our MMT-R exhibited transfer properties similar to the non-dyed clays but was detectable starting from 1 ppb by fluorescence and only from 0.5 ppm by turbidity. More contaminated soil adsorbed the MMT-R better than the pure one and therefore the reduction of influent turbidity may have the unintended effect of decreasing soil adsorption capacity. (C) 2011 Elsevier B.V. All rights reserved.