Comparison of Toxicity to Plants among Al8+, AlSO4+, and Al-F Complex Ions

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Abstract
Behavior of Al-containing ions at various pHs was studied by using solutions to which 10/3 mmol/liter of Al(OH)3 and 10/2 mmol/liter of H2SO4 or 0.2 or 2 mmol/liter of NaF were added, and the following results were obtained: (a) Total Al concentration starts to decrease when the pH increases above about 4.0 and reaches below 1 ppm at about pH 4.8. However, when 2 mmol/liter of NaF is present in the solution, the total Al concentration is higher at corresponding pHs than the above values. (b) When sulfate or fluoride ions are absent, Al8+ predominates at pH 4, and Al(OH)2 + predominates at pH 5. (c) In the presence of sulfate ion, AlSO4 + predominates followed by Al8+ at pH 4, while AlSO4 + and Al(OH)2 + predominate at pH 5. (d) When fluoride ion is present at 2 meq F/liter, Al8+ predominates although there is a considerable amount of AlF2+ at pH 4, and AlF2 + predominates at pH 5. By measuring the elongation of barley roots which were grown in solutions with and without 10/3 mmol/liter of Al(OH)8 in combination with and without CaSO4, CaCl2, or NaF at various levels, and at different pHs, the following conclusions were reached: (a) Elongation of barley roots is retarded by Al8+, and the degree of retardation is controlled by the activity of AIH rather than by the concentration. (b) AlSO4 + and Al-F complex ions are far less toxic than Al8+. (c) The presence of K, Ca, and Mg at adequate concentrations alleviates the toxic effect of AI8+.