Fig. 5. Effects of background electrolyte concentrations (•, 0.01 M CaCl₂; , 0.1 M CaCl₂) on the amount of 2,4-D adsorption on untreated UG5 soil as a function of equilibrium pH. Reaction time, 4 h; initial 2,4-D concentration, 22.6 µM (5.0 mg L^–1); the amount of soil, 50 g L^–1 (oven-dry basis). Had the soil adsorbed all 2,4-D in this experiment, the amount of 2,4-D adsorption would have reached 0.452 mmol kg^–1.