Sorption of 2,4-Dichlorophenoxyacetic Acid by Model Particles Simulating Naturally Occurring Soil Colloids

Abstract

Binary and ternary model particles containing montmorillonite, ferrihydrite, and humic acid (HA) were used to determine the changes in the sorption behavior of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) upon the interassociation of these three major soil constituents. On single sorbents, 2,4-D sorption was high with S-type isotherms on ferrihydrite, moderate with L-type isotherms on HA, and zero on montmorillonite. In binary sorbents, ferrihydrite and humic acid coatings on montmorillonite provided sorption sites for 2,4-D, although the exclusion of the anionic form from highly charged clay surfaces partially obscured the role of Fe and HA as sorbents of 2,4-D. Sorption of 2,4-D on ferrihydrite-HA binary particles was not very different fromthat on pure ferrihydrite because most of the ferrihydrite surface area was from micropores being not accessible to large humic macromolecules and hence remained available for herbicide sorption. In ternary sorbents HA coatings reduced the sorption of 2,4-D by the montmorillonite-ferrihydrite binary complex, indicating that HA blocked many of the sorption sites provided by the Fe coatings. This work shows that the amount and nature of the surface that remains available after the interassociation of single soil constituents is a critical parameter in determining the sorptive behavior of the resultant aggregate for ionizable contaminants such as 2,4-D. Thus, the use of calculated sorption parameters such as K oc , K ow , K mineral , or K Fe , for modeling contaminant behavior in aquatic or soil environments may result in serious deviation from the reality.

Spatial variability of soil properties and 2,4-D sorption in a hummocky field as affected by landscape position and soil depth

“…Although soil organic carbon content had the greatest overall influence on 2,4-D sorption in the B horizon, very little of the sorption could be accounted for by this property or any of the other soil properties. The presence of iron oxides is known to increase 2,4-D sorption in soil (Reddy and Gambrell 1987;Celis et al 1999), and were visually observed as rust flecks in B horizon soil samples, but not quantitatively measured. It is generally accepted that as soil organic carbon content decreases with soil depth, other soil properties play an increasingly important role in 2,4-D sorption (Reddy and Gambrell 1987;Green and Karickhoff 1990;Wauchope et al 2002).…”

Soil Chemical Insights Provided through Vibrational Spectroscopy

“…Others have used FTIR to investigate the interaction of anionic herbicides and herbicide degradation products with metal oxides to determine the types of complexes and structures formed upon adsorption. Celis et al (1999) and Goyne et al (2004) investigated mechanisms of 2,4-dichlorophenoxyacetic acid (2,4-D) sorption to metal oxide surfaces using transmission FTIR and ATR-FTIR, respectively. Both interpreted the acquired spectra as indication that 2,4-D sorbed to variable charge mineral surfaces via electrostatic interaction between the carboxylate group and ^Metal-OH 2 + surface functional groups on Al and Fe oxides.…”

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

“…S-type isotherms are commonly observed for the sorption of polar pesticides on polar surfaces from water, particularly when the pesticide also contains a hydrophobic moiety that may result in hydrophobic intermolecular attraction between adjacent pesticide molecules in the sorbed state [27,[38][39][40]. Such intermolecular attractions are favored at higher surface coverages, thus explaining the enhanced sorption at higher fungicide concentrations (cooperative sorption) characteristic of S-type isotherms [38].…”