Influence of commercial formulation on leaching of four pesticides through soil

Studies with small soil columns (2 cm i.d. x 5.4 cm depth) compared leaching of four pesticides added either as technical material or as commercial formulations. Pesticides were selected to give a gradient of solubility in water between 7 and 93 mg L-1, comprising azoxystrobin (emulsifiable concentrate, EC, and suspension concentrate, SC), cyproconazole (SC), propyzamide (SC) and triadimenol (EC). Columns of sandy loam soil were leached with 6 pore volumes of 0.01M CaCl2 either 1 or 7 days after treatment. Separate experiments evaluated leaching of triadimenol to full breakthrough following addition of 18 pore volumes of 0.01M CaCl2. The mass of pesticide leached from columns treated with commercial formulation was significantly larger than that from columns treated with technical material for all compounds studied and for both leaching intervals (two-sided t-tests, p<0.001). This difference was conserved when triadimenol was leached to full breakthrough with 79 ± 1.2 and 61 ± 3.1% of applied triadimenol leached from columns treated with formulated and technical material, respectively. There were highly significant effects of formulation for all pesticides (two-way ANOVA, p<0.001), whereas leaching interval was only significant for azoxystrobin EC formulation and cyproconazole (p <0.001 and 0.021, respectively) with greater leaching when irrigation commenced 1 day after treatment. Leaching of azoxystrobin increased in the order technical material (6.0% of applied pesticide) < SC formulation (8.5-9.1% of applied) < EC formulation (15.8-21.0% of applied). The relative difference between leaching of formulated and technical pesticide increased with pesticide solubility in water, increasing from a factor of 1.4 for the SC formulation of azoystrobin to 4.3 for the SC formulation of triadimenol. Experimental systems differ markedly from field conditions (small columns with intense irrigation). Nevertheless, results indicate the need to consider further the influence of co-formulants in pesticide formulations on behaviour of the active ingredient in soil.