pH-altered interaction of aluminium and fluoride on nutrient uptake, photosynthesis and other variables of Chlorella vulgaris

This study presents information on the pH-induced toxicity of AlCl3, AlF3, NaF and AlCl3 + NaF on growth, nutrient uptake, photosynthesis, photosynthetic electron transport, enzymes of nitrogen and phosphorus metabolism and ATPase activity of Chlorella vulgaris. Both PS I and PS II were severely inhibited by the combination of AlCl3 + NaF followed by AlF3, AlCl3 and NaF. Inhibition of acid phosphatase activity was more pronounced than alkaline phosphatase. In general, toxicity of all the test chemicals increased with a downshift in pH. The interaction of AlCl3 and NaF produced additive effect at pH 6.8, and synergistic at pH 6.0 and 4.5. The combination of AlCl3 + NaF did not produce significant difference in the activity of Mg2+ and Ca2+-ATPase in the medium supplemented with 60 and 100 mu M PO43- at pH 6.8. Compared to 60 mu M PO43-, the test organism grown in 100 mu M PO43- containing medium depicted significant increase in Mg2+ and Ca2+-ATPase activity at pH 6.0 and 4.5. Infra-red spectra revealed the formation of AlF4- at pH 6.0 and 4.5 in AlCl3 + NaF supplemented medium as well as in the algal cells. Aluminium uptake from the medium containing AlCl3 decreased in the presence of PO43-. This study suggests that phosphate restricts the entry of Al into the cell, while fluoride promotes it. AIF, toxicity could be due to its interference with phosphate binding site of ATPase thereby arresting the release of energy. (C) 1998 Elsevier Science B.V. All rights reserved.