Fig. 7. Adsorption distribution coefficients (K_d values) obtained at an initial pesticide concentration of 250 µg/L (1.04–1.21 µmol/L) for 2,4-D, mecoprop, and bentazone on iron oxides as a function of the CaCl₂ concentration. The solution conditions are: temperature = 10°C and pH 4.6 ± 0.1. Error bars indicate standard deviation (may be covered by the symbols).