Forms of Aqueous Aluminum in Acidified Catchments of Central Ontario: A Methodological Analysis

Abstract

Separating the different forms of aqueous aluminum is essential for determining their relative toxicity in acidified streams and lakes. A short extraction with oxine at pH 8.3 separates inorganic monomeric and organic aluminum from the polymeric and amorphous forms. The organic fraction can be eliminated by equilibrium dialysis prior to extraction. In many cases, the inorganic fraction can also be estimated from free and total fluoride measurements. The two methods agree well in artificial solutions (R2 = 0.997) and reasonably well in natural waters (R2 = 0.82), although the computed estimates tend to be slightly lower than the directly measured values. During spring snowmelt in the Muskoka–Haliburton region of central Ontario, very little polymeric and amorphous aluminum was found, and most of the inorganic monomeric fraction was in the fluoride complexes. I present an empirical model that predicts inorganic monomeric aluminum in these waters (R2 = 0.90) using total organic carbon and the aluminum measured by a short extraction without dialysis.