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 AlCl 3, AlF 3, NaF and AlCl 3+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 AlCl 3+NaF followed by AlF 3, AlCl 3 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 AlCl 3 and NaF produced additive effect at pH 6.8, and synergistic at pH 6.0 and 4.5. The combination of AlCl 3+NaF did not produce significant difference in the activity of Mg 2+ and Ca 2+-ATPase in the medium supplemented with 60 and 100 μM PO 4 3− at pH 6.8. Compared to 60 μM PO 4 3−, the test organism grown in 100 μM PO 4 3− containing medium depicted significant increase in Mg 2+ and Ca 2+-ATPase activity at pH 6.0 and 4.5. Infra-red spectra revealed the formation of AlF 4 − at pH 6.0 and 4.5 in AlCl 3+NaF supplemented medium as well as in the algal cells. Aluminium uptake from the medium containing AlCl 3 decreased in the presence of PO 4 3−. This study suggests that phosphate restricts the entry of Al into the cell, while fluoride promotes it. AlF 4 − toxicity could be due to its interference with phosphate binding site of ATPase thereby arresting the release of energy.