Variation of the stability of complexes of Al(III) with a fulvic acid extracted from a humic cambisol soil in the pH range three to five
- LAQUIPAI, Porto (Portugal). Faculdade de Ciencias
- Univ. de Santiago de Compostela (Spain). Dept. de Quimica Fisica
- Univ. de Vigo (Spain). Dept. de Quimica Fisica
The interaction of the aluminum ion [Al(III)] with the major constituent of soil organic matter, fulvic acids (FA), was investigated in the acid pH range. The complexation of a FA extracted from a humic cambisol soil (at a concentration of 80 mg/L) when titrated with Al(III) were monitored directly by synchronous fluorescence (SyF) spectroscopy at five pH values (3.0, 3.5, 4.0, 4.5, and 5.0), at 25 C and with 0.1 N KNO{sub 3}. Inverted second derivative SyF data were preprocessed by a self-modeling mixture analysis method to obtain fluorescence enhancement profiles as a function of the increasing Al(III) concentration. Assuming that the concentration of complexes formed between Al(III) and FA is proportional to the fluorescence intensity, these profiles were adjusted to a 1:1 complexation model and the following conditional stability constants (log K{sub c}) were calculated (standard deviation in parenthesis), pH = 3.0, 4.3 (1); pH = 3.5, 4.3 (1); pH = 4.0, 5.0 (1); pH = 4.5, 5.1 (3); and pH = 5.0, 5.3 (2). These constants show that the stability of the complexes decreases markedly at pH < 4. The environmental implication of this result is that an increase in the extent of the dissociation of the Al(III) + FA complexes is expected at pH < 4, increasing the free Al(III) concentration and probably its ecotoxicity.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 556542
- Journal Information:
- Environmental Toxicology and Chemistry, Journal Name: Environmental Toxicology and Chemistry Journal Issue: 9 Vol. 16; ISSN ETOCDK; ISSN 0730-7268
- Country of Publication:
- United States
- Language:
- English
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