Adsorption–Desorption of Aminomethylphosphonic Acid (AMPA) in Sandy Soil Amended with Cow Dung and Rice Husk Ash

Abstract

The present study investigates adsorption–desorption of aminomethylphosphonic acid (AMPA)—a residue of glyphosate herbicide—by sandy soil added with cow dung or rice husk ash. Adsorption study was conducted using different concentrations of AMPA in 0.01 M CaCl2. Desorption study followed immediately by adding 0.01 M CaCl2 solution without any AMPA. The concentration of AMPA in both studies was analysed using high performance liquid chromatography coupled with a fluorescent detector. The result revealed an increase in adsorptive removal of AMPA from the soil due to the addition of cow dung or rice husk. The isotherm data of AMPA adsorption by control and amended soils best fitted the Freundlich model (r2 ≥ 0.701). The Freundlich’s constant (KF) for AMPA was highest in the soil + rice husk ash (7.268 mg g−1), followed by cow dung amended soil (5.692 mg g−1) and then control (4.906 mg g−1). The 1/n coefficient for AMPA in both soils was >1, indicating cooperative adsorption. However, the results also showed that soil applied with cow dung and rice husk ash had respective increases of 4.22% and 1.784% in AMPA desorption compared to the control. Therefore, the addition of cow dung and rice husk ash can increase AMPA mobility in this soil making it susceptible to degradation or groundwater contamination.