Colloid-facilitated transport of metolachlor through intact soil columns

Abstract

This study evaluated the role of water dispersible colloids with diverse physicochemical and mineralogical characteristics in facilitating the transport of metolachlor through macropores of intact soil columns. The soil columns represented upper solum horizons of an Alfisol in the Bluegrass region of Kentucky. Three different colloid suspensions tagged with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl)acetamide] were introduced at a constant flux into undisturbed soil columns. The eluents were 949 950 SETA AND KARATHANASIS collected and analyzed periodically for colloid and metolachlor concentrations. Colloid recovery in the eluents ranged from 54 to 90 %. The presence of colloids enhanced the transport of metolachlor by 22 to 70 % depending on the colloid type and mobility. Colloids with higher pH, organic carbon, cation exchange capacity (CEC), total exchangeable bases (TEB), surface area (SA), and electrophoretic mobility (EM), showed better mobility, greater affinity for interaction with the herbicide and, thus, greater potential to co-transport metolachlor. In contrast, increased level of kaolinite, Fe, and Al inhibited metolachlor adsorption and transport. In spite of the increased transportability of metolachlor by the presence of soil colloids, the colloid bound herbicide portion accounted for a very small part of the observed increase. This suggests that surface site exclusion mechanisms and preferential sorption induced by the presence of colloids are more important than ion exchange phenomena in promoting herbicide mobility in subsurface environments.

Movement of pendimethalin, ioxynil and soil particles to field drainage tiles

“…It has been suggested that preferential flow may contribute significantly to the movement of pesticides in soil,7, 11, 15 although the transport mechanisms are not known in detail. A number of studies have dealt with the issue of colloid‐facilitated transport 16. 17 Structural heterogeneity, in particular the presence of continuous macropores, may enhance the mobility of particles and sorbed contaminants because adsorption, sedimentation and sieving are less pronounced in large pores 18.…”

Nanoparticles in the Water Cycle

“…4.12) (Seta and Karathanasis, 1996). This is the result of the higher adsorption coefficient (3-to 5-fold) of metolachlor over that of atrazine for soil and colloid surfaces.…”

Role of livestock effluent suspended particulate in sealing effluent ponds

“…As per the above discussion, Ives (1975) concluded that sedimentation was likely to be unimportant due to the small diameter of colloidal particles. Some studies have investigated the passing of colloidal materials through soil columns (Awedat, 2014;Lahav, 1980;Seta and Karathanasis, 1996) with the major findings being that greater macroporosity causes greater colloidal transport and that there is usually a higher concentration of attached colloids nearer the surface layers. Of importance, a study by Toran and Palumbo (1992) sought to determine how influential chemical effects were on colloidal attachment via infiltration of artificially fractured columns.…”