EVIDENCE FOR A PHYTOTOXIC HYDROXYALUMINUM POLYMER IN ORGANIC SOIL HORIZONS

The toxicity of Al that has been mobilized in soil, streams, and lakes through acid deposition primarily has been attributed to mononuclear Al species. Polynuclear Al species are more toxic than mononuclear species, but they have not been considered to be significant in the environment. Aluminum-27 nuclear magnetic resonance (NMR) spectra of forested spodosol soil horizon samples show the presence of polynuclear AlO4Al12(OH)24(H2O)12(7+). The AlO4Al12(OH)24(H2O)12(7+) species accounted for 30 percent of the aqueous Al observable by NMR, and this could make a significant contribution to the toxicity of the Al in these soils.