Colloids and Colloid-Facilitated Transport of Contaminants in Soils: An Introduction

Abstract

as a third phase, thus enhancing the transport of strongly sorbing contaminants (McCarthy and Zachara, 1989).Until some two decades ago, it was believed that only the soil liquid and gaseous phases were mobile and could facilitate the transport of chemicals and nutrients through the vadose zone. It is now generally SOURCES OF MOBILE SOIL COLLOIDS accepted that also part of the soil solid phase is mobile, and thatThe tendency of soil colloids to disperse from soil mobile organic and inorganic soil colloids may facilitate chemical transport. However, the magnitude and significance of these colloidal aggregates in response to infiltration of water is a natural transport processes are yet to be determined. It is essential to examine phenomenon, sometimes even leading to the developwhether current models for transport and fate of chemicals in soil ment of illuvial subsurface horizons with higher contents and groundwater need to be revised. The collection of papers in this of clay compared with the upper eluvial horizons. Microspecial section of Vadose Zone Journal mainly take their origin, morphological features showing deposits of clay skins but not exclusively, from an international workshop "Colloids and on ped faces and at the interface of water-conducting Colloid-Facilitated Transport of Contaminants in Soil and Sediments" pores represent evidence of such colloid translocation held at the Danish Institute of Agricultural Sciences, Denmark, 19-20 (Buol and Hole, 1961). Dispersion of colloids is also Sept. 2002. The workshop was organized to review our present knowlsuspected to be responsible for affecting soil physical edge of colloid behavior and transport in porous media and the possi-properties such as surface crusting, surface erosion, wability of colloid-bound transport of contaminants and nutrients in soil and groundwater. Here we will first give a brief introduction to the ter infiltration, and hydraulic conductivities (e.g., Miller topic of mobilization and transport of colloids in the vadose zone, and Baharuddin, 1986;Shainberg et al., 1992). The source and highlight previous evidence of colloid-facilitated transport. We of mobile colloids in the vadose zone is generally considthen introduce the review and technical papers in the special section. ered to be the in situ release of water-dispersible colWe hope that the information provided in this special section will loids. Colloids are operationally defined as particles belead to improvements in our understanding and associated conceptual tween 1 to 10 nm and 2 to 10 m in diameter (e.g., models of contaminant transport and fate in soil.

Prions in the environment

“…Colloid-facilitated transport has been shown to be a significant transport process for many strongly-sorbing contaminants. 102 In addition, infectious prions can form aggregates of colloidal size 95 and might be transported unassociated. Macro-pore colloid-facilitated transport could quickly move prions into groundwater or surface waters and therefore warrants further study.…”

Carbon nanomaterials in clean and contaminated soils: environmental implications and applications

“…The ability of natural colloids to assist in the transport of organic contaminants has been well documented and reviewed (De Jonge et al, 2004;Sen and Khilar, 2006;Li et al, 2013). Typically, hydrophobic compounds such as PCBs and PAHs have limited environmental mobility due to strong sorption to SOM.…”

“…Typically, hydrophobic compounds such as PCBs and PAHs have limited environmental mobility due to strong sorption to SOM. Kan and Tomson (1990), however, demonstrated that high concentrations of colloidal materials such as DOM may enhance the transport of hydrophobic compounds such as phenanthrene and naphthalene by a factor of 1000 or greater, with possible implications for the spread of contamination and groundwater quality (De Jonge et al, 2004). Although CNMs may be tailored to suit specific requirements, their behaviour is not necessarily different to colloids naturally occurring in the environment (Colvin, 2003;Lead and Wilkinson, 2006).…”

Hard X-ray Fluorescence Microscopy to Determine the Element Distribution of Soil Colloids in Aqueous Environment

“…As a consequence, the colloid-facilitated matter transport of non-or barely soluble matter has been ignored for a long time, leading to significant underestimations of, for example, the transport of toxicants through the soil matrix [3]. The same mechanism determines the uptake and release of nutrients in soils and their bioavailability for plants, influencing directly, for example, the growth of plants [4].…”