*3.4. Equilibrium Solutions pH*

For all soils the acid initial solutions, pH led to acidic equilibrium solutions pH (Figure 4). In particular, the equilibrium solutions' pH values for alkaline soils showed a decrease between one and three units as the concentration of added Se(IV) increased, while for acid soils the corresponding decrease was sharp for a 10 mg/L initial Se(IV) concentration, remaining almost constant thereafter for higher Se(IV) concentrations. Alkaline soils 3 and 4 showed higher resistances to pH changes than alkaline soils 1 and 2, probably due to the higher buffering capacity attributed to the higher carbonates content (Table 1).

**Figure 4.** Equilibrium solutions pH values. Dashed line shows the initial solutions pH values. Soil pH values are presented in the incorporated frame.
