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Fig. 3. Kinetics of 2,4-D concentration changes in aqueous solution in the presence of an Andosol (untreated UG5 soil) at equilibrium pH 4.5, 5.0, 5.5, 6.0, and 6.5. Initial 2,4-D concentration, 22.6 µM (5.0 mg L–1); the amount of soil, 50 g L–1 (oven-dry basis); background electrolyte, 0.01 M CaCl2. First, a relationship between 2,4-D concentration in aqueous solution in the presence of untreated UG5 soil and equilibrium pH was drawn at each reaction time (6 to 7 plots between pH 4 and 7), and then 2,4-D concentration at equilibrium pH 4.5, 5.0, 5.5, 6.0, and 6.5 at each reaction time was read from the relationship and plotted on this figure. The equilibrium pH value increased 0 to 0.5 units with reaction time depending on the initial pH value.
