Competitive sorption of atrazine and metolachlor in soil

Abstract

Atrazine and metolachlor co-application to soil created competitive sorption between the two herbicides, producing smaller partitioning coefficients than for separate atrazine and metolachlor applications. The partitioning coefficients for both compounds were also less when applied in a commercial formulation, compared with separate analytical-grade applications. Since the Freundlich slope of the isotherms was less than unity (0.83 to 0.87), the sorption strength of the herbicides decreased with increasing solution concentrations. Based on the Freundlich adsorption values obtained, this study concludes that atrazine and metolachlor co-applications on agricultural fields have the potential to increase the mobility of these herbicides in soil, thereby also increasing the risk for groundwater contamination.

Pesticide soil sorption parameters: theory, measurement, uses, limitations and reliability

“…179 However, any sorption isotherm which covers a wide concentration range (say, > two orders of magnitude), even if the whole range is at very low concentrations, will typically be non‐linear,180 presumably because there are only a small number of sites of each energy level 166. Competition for this small number of similar‐energy sites is demonstrated by solutes exhibiting non‐linear Freundlich‐type isotherms even when solute concentrations are quite dilute 181–183. Chiou and Kile184 showed that non‐linear sorption at very low concentrations may be followed by linear sorption at higher ranges; this suggests that the distribution of sorbent/adsorbent energies is not a simple curve.…”

Phosphate fertilizer impacts on glyphosate sorption by soil

“…The impact of phosphate on reducing glyphosate sorption was stronger for synthesized Fe and Al-oxides than for pure clay-minerals (Gimsing and Borggaard, 2002b). All batch equilibrium studies utilized analytical-grade glyphosate, while herbicide products applied on agricultural land contain other ingredients that could impact the sorption of the active ingredient by soil (Farenhorst and Bowman 1998). Hence, in evaluations of the impact of phosphate additions on glyphosate sorption, it is desired to include a commercially available glyphosate formulation in the study.…”

The Effect of Propanil Co‐application on 2,4‐D Sorption by Soil

“…[2] Freundlich values are usually obtained using single herbicide compounds but, when in soil, herbicides may behave differently alone than when applied in combination with others. [3 -6] For example, the sorption of atrazine by soil was reduced when other triazines [5] or metolachlor [6] were present and competed with atrazine for sorption sites in soil.…”