Assessing the Rhizotoxicity of the Aluminate Ion, Al(OH)₄⁻

Abstract

Dissolved aluminum (Ill) in acidic soils or culture media is often rhizotoxic (inhibitory to root elongation). Alkaline solutions of Al are also sometimes rhizotoxic, and for that reason toxicity has been attributed to the aluminate ion, AI(OH)4-. In the present study, seedlings of wheat (Triticum aestivum L. cv Tyler) and red clover (Trifolium pratense L. cv Kenland) were cultured in aerated aluminate solutions at pH 8.0 to 8.9. The bulk phases of these solutions were free of reactive polynuclear hydroxy-AI (including the extremely toxic species AlO4Al12 [OH] species (15, 26). That one or more ofthese species is rhizotoxic has been known for many decades (7), but only recently has there been progress in determining the relative toxicities of the various species (4, 8, 12-14, 19, 21, 22). Evidence for the toxicity of a polynuclear Al species has been offered several times (2,21,22, 27), and this species has now been identified as Al13 ' (22). This species is easily prepared in artificial solutions, but upon aging, All3 undergoes a conversion to other Al species that are unreactive with commonly used assay reagents and may comprise microcrystalline gibbsite or other solid-phase Al (3,22). Al,3 is at least 10-fold more rhizotoxic than A13+ (22), and the possibility of its occurrence is a complicating factor in the study ofthe toxicity of other species (13). (14). Perhaps protonation of cell surface sites reduces Al3+ binding. In addition, Al,3 may have accumulated in the root free space as mononuclear hydroxy-Al increased in the bulk media.Al in alkaline fly ash (9, 25), bauxite residue (6), and hydroponic culture media (6) appears to be toxic, and that toxicity has been attributed to aluminate (Al[OH]4) which, according to species computations, would constitute >99% of the mononuclear hydroxy-Al at pH > 7.9. However, these media were complex, and, appropriately, the authors made no attempt to compute the species composition. In addition, no attempt was made to detect Al13, whose toxicity was not widely known at the time of those studies.The present experiments were performed as part of an ongoing investigation of the relative rhizotoxicity of Al species. The major emphasis of the study was to employ simple solutions whose species composition could be computed and to ensure the absence of Al,3 in the bulk phase of the culture media. MATERIALS AND METHODS Seedling CultureSeedlings of wheat (Triticum aestivum L. cv Tyler) and red clover (Trifolium pratense L. cv Kenland) were cultured at 25°C in aerated, 500-mL solutions as described previously (10, 13). All alkaline solutions were aerated overnight prior to the introduction of seedlings. After 2 d, root lengths were measured and the culture media were assayed for Al by the ferron method to be described. In a typical experiment intended to test the apparent toxicity of aluminate, the culture media were prepared by adding 2.95 mL of 1 M NaHCO3, 0 to 50 mL of a 1 mm stock solution of LiAl02 (in 1 mM NaOH), 50 to 0 mL of a 1 mm stock solution of LiCl (in 1 1...

Characterization of physical and chemical properties of spent foundry sands pertinent to beneficial use in manufactured soils

“…The 39 SFS had a median soluble concentration of macro nutrients: Ca, Mg, K, P, and S of 32.5, 13.5, 27.3, 0.391 Given the neutral to high pH of the SFS, it is unlikely free Al +3 is present, but rather hydoxy or polymeric Al. It is unlikely the soluble Al found in the SFS will remain in solution once blended with other components in a soil mixture (Fuller and Richardson 1986;Kinraide 1990). However, soluble Al in finished soil blends should be evaluated to determine if potential Al phytotoxicity issues could arise.…”

The Bioavailability and Toxicity of Aluminum in Aquatic Environments

“…Thus, it is difficult to separate experimentally whether dissolved or polymeric Al species can best explain pH-dependent algal toxicity. Given that some forms of polymeric Al (i.e., the Al 13 cation) can be more toxic to terrestrial plants than dissolved Al species (Parker et al, 1989;Kinraide, 1990), it is critical that we improve our understanding of its relative potency in aquatic species.…”

Interacción Rhizobium Leguminosarum Bv Trifolii Y Hongos Micorrícicos en Un Andisol Con Diferentes Niveles De Saturación De Aluminio

“…Richardson et al (1988) observaron en T. repens que el Al afectó el crecimiento de Rhizobium trifolii tanto en solución como en la rizósfera de la planta. Las especies y variedades dentro de las especies vegetales muestran grandes diferencias en la susceptibilidad a la toxicidad por Al (Ma, 2000), siendo las leguminosas las más susceptibles por el efecto detrimental producido en el proceso de nodulación (Kinraide, 1990). Con el porcentaje de saturación de Al mayor (SAl 4 ) las cepas R-113 y R-115 resultaron ser las más tolerantes, con incrementos de aproximadamente 80% y 60% sobre el testigo con cepas nativas, mientras la cepa R-109 resultó ser la más sensible.…”