Effect of particle size on copper oxychloride transport through saturated sand columns

Understanding the mechanisms behind the transport of particulate contaminants in porous media is crucial with a view to evaluating their potential impact on the environment. Much of the copper used in agriculture is sprayed as colloidal copper oxychloride, and despite its potential environmentally adverse consequences, colloidal transport of particulate formulations of copper remains poorly understood. In this work, transport of copper colloids from a commercial copper oxychloride based fungicide formulation was studied by measuring its breakthrough in saturated quartz sand columns. The influence of ionic strength and flow rate on the test results suggests that retention of copper oxychloride based colloids is governed by weak forces. The particle deposition dynamics of the studied copper formulation was consistent with a two-site kinetic attachment model. The proposed colloid retention mechanisms are highly sensitive to the fungicide particle size. A comparison of our test results with reported data for other copper oxychloride wettable powder fungicide formulations revealed that transport of copper oxychloride is strongly influenced by its particle size. This is consistent with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), but only if binding occurs at the secondary minimum in the potential, where attachment is less favorable with small particles. The influence of particle size is also consistent with the results of previous studies where deposition was ascribed to retention at a secondary minimum. The mobility of colloidal formulations of these copper-based fungicides in saturated porous media increases with increasing particle size.