Colloid-Mediated Transport of Contaminants

Contaminants retained on colloid surfaces may be transported by flowing water through the vadose zone and reach the groundwater or be relocated on the land surface by runoff processes. Operationally defined as particles between 1 j,m and 1 nm in size, colloids in the subsurface may be of mineral, organic, or biological origin. 

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A series of field and laboratory experiments identified the spatial redistribution of contaminants by surface runoff and contamination of the subsurface by vertical transport of colloids. These findings demonstrate that colloidal-mediated transport of contaminants is a major environmental hazard. 

Colloidal-mediated transport of contaminants into the subsurface is illustrated by the behavior of heavy metals and organic pesticides that originate from agricultural practices. 

Sources Adapted from Kretzschmar, R. et al., Adv. Agron., 66, 121, 1999 Sen, T.K. and Khilar, K.C., Mobile subsurface colloids and colloid-mediated transport of contaminants in subsurface soils, in Birdi, K.S. (Ed.), Handbook of Surface and Colloid Chemistry, 3rd edn., Taylor Erancis Group/CRC Press, 2009, pp. 107-130. 

Transport of contaminants by surface runoff is illustrated in the experimental results of Turner et al. (2004), which deal with the colloid-mediated transfer of phosphorus (P) from a calcareous agricultural land to watercourses. Colloidal molybdate-reactive phosphorus (MRP) was identified by ultrafiltration associated with particles between l am and Inm in diameter. Colloidal P compounds can constitute a substantial component of the filterable MRP in soil solution and include primary and secondary P minerals, P occluded or adsorbed on or within mineral or organic particles, and biocolloids (Kretzschmar et al. 1999). 

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