One mechanism by which certain plants tolerate high concentrations of aluminum in the soil is for their roots to exude organic acids; these acids detoxify the Al(III) through a chelation reaction. For example, buckwheat and hydrangea endure aluminum-rich soil by complexing Al(III) with oxalate and citrate, respectively, in their root zones. The solubilities of several organic acids (oxalic, succinic, and citric) were measured in water and in 0.5M Al(III) as a function of the temperature. The heats of solution of these acids were then determined by use of the van't Hoff equation; their experimental heats in water compared favorably with reference values. With respect to measurements in water, the presence of Al(III) doubled the solubilities of oxalic and succinic acids at 25 C, and halved their heats of solution. Such effects are evidence for chelation between Al(III) and the organic acid. Surprisingly, Al(III) had negligible effect on both the solubility and heat of solution of citric acid in water. The solubilities of oxalic and citric acids were also measured in 0.5M solutions of other metal ions; Fe(III), Fe(II), and U(VI) all had negligible effect on the solubilities, but Mo(VI) as molybdate significantly enhanced the solubilities. Plants using the detoxification mechanism of exuding organic acids from their roots may thus concentrate molybdenum in bioremediation efforts. In addition, hydrangea may also be able to tolerate Mo(VI)-rich soils, allowing the substitution of Mo(VI) for Al(III) in the bluing of hydrangea blooms.