Differential Transport of Atrazine and Glyphosate in Undisturbed Sandy Soil Column

With increasing awareness and concern for environmental quality, it is important to study the fate of pesticides in the subsurface. Laboratory studies were conducted to determine the behavior of atrazine and glyphosate within the root zone of an undisturbed sandy soil in Jianghan Plain, central China. Chloride as a tracer for water movement was applied to the soil as KCl for 26 hours before pesticide application for another 160 hours. Glyphosate, atrazine, and Cl concentrations (conc.) were determined as a function of time in breakthrough curves (BTCs). Atrazine BTC was fitted better in convection-dispersion equation equilibrium model. For glyphosate, however, a two-site non-equilibrium model was chosen. Leaching rate of atrazine from sandy soil was much higher than that of glyphosate and it took longer for glyphosate to leach through the column due to stronger sorption and degradation to its major metabolite, AMPA (aminomethylphosphonic acid, CH₆NO₃P), which was detected (up to 8890 ng/l) in the final leachate.