Cadmium sorption by montmorillonite from solutions in the 15 to 120 ppb range was studied in the presence of increasing concentrations of NaClO4, NaCl, and Na2SO4 solutions. The ionic strengths ranged from 0.01 to 1.00. Increasing ionic strengths decreased the amount of Cd sorbed on the clay surfaces. The percentage sorbed decreased from around 90% for I = 0.01 to about 50% for I = 1.00 in the ClO4 systems. The sorption of Cd in the chloride system was in the range between 25 to 50% less than the ClO4 systems for the same ionic strength. This was attributed to the presence of uncharged and negatively charged complexes of Cd with Cl ligands. This fact has some implications, especially in arid zone soils where high Cl concentrations in soil solutions are not unusual; there, Cd will behave mainly as a neutral species (CdCl20) and as an anion (CaCl3‐ and CdCl42‐), rather than as a cation (Cd2+).The SO4 systems showed a moderate decrease in the amount of Cd sorbed with respect to the ClO4 systems for the same salt concentrations. This observation was interpreted as due to the presence of a fraction of Cd in solution as the CdSO40 species.

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Bulk precipitation was daily collected and individual pH measured at the Trachypogon savannas, Venezuela, over a consecutive 3‐year period. The volume‐weighted mean pH as calculated, were 5.8, 5.6 and 5.8 for 1981, 1982 and 1983, respectively. The annual variation of pH ranged from 4.9 to 6.9; 4.8 to 6.3 and 5.4 to 6.8 units in 1981, 1982 and 1983, respectively. However, in this savanna area, which is relatively remote from heavy sources of industrial pollution, the annual proportion of daily rains with pH < 5.0, occurring mainly at the onset and end of the wet season, were 2.0, 3.0 and 0.0% for 1981, 1982 and 1983, respectively.

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