Phytotoxicity of aluminium-fluoride complexes and their uptake from solution culture by Avena sativa and Lycopersicon esculentum

Avena sativa (oats) and Lycopersiconesculentum (tomatoes) were grown in dilute nutrientsolutions supplemented with Al only, F only or acombination of both. In solutions containing Al andF, shoot growth was limited when predicted Al_r(Al³⁺, AlOH²⁺ and Al(OH) )activities were < 0.1 M, activities three orders ofmagnitude lower than the critical value determinedwith Al only. The data suggest that at the activitiesused in these experiments, Al_r is most toxic,AlF²⁺ and AlF are toxic to a lesserextent, and AlF₃, AlF and F^-are least toxic. Fluoride concentrations in shootsgrown in solutions correlated best with positivelycharged AlF species (i.e.AlF²⁺, AlF ) and the molar ratio ofF:Al in most plants shoots was about 3:2. However,when activities of positively chargedAlF species were low (< 50 M)and theactivity of AlF₃ species high (500 M) the molarratio of F:Al in plant shoots suggested AlF₃ wastaken up. These findings are discussed in relation toplant uptake and toxicity. Measured concentrations of Al_r and F^- insolutions containing Al and F were compared withconcentrations predicted by a computer model(GEOCHEM-PC). The method for measuring F^-concentrations, using a non-complexing buffer and Fion-selective electrode, gave good agreement withpredicted F^- concentrations. The8-hydroxyquinoline method for measuring Al_rconcentrations did not agree with predictedconcentrations, highlighting the limitations of thismethod when measuring Al_r in the presence of F ina multi-ligand system with high concentrations of Fand Al.