Effects of aluminum and acid on calcium uptake by the crayfishOrconectes virilis

Abstract

Aluminum increases in concentration in acidified waters and is sometimes more toxic to aquatic organisms at acidic than at neutral pH. This paper examined the interaction of pH and Al in inhibiting uptake of Ca⁺⁺ from lake water by postmolt crayfish,Orconectes virilis (Hagen). Aluminum at 200 μg/L in non-acidified media had no effect on⁴⁵Ca uptake. Media at pH 5.5 without Al reduced⁴⁵Ca uptake to 30% of that in non-acidified media. Aluminum at each of the concentrations of 200, 500 or 1,000 μg/L in media at pH 5.5 reduced⁴⁵Ca uptake slightly more, to about 20% of that in non-acidified media. The degree of inhibition of⁴⁵Ca uptake by Al in acidified media was not related to its concentration. Lack of dose-response may be explained by the limited solubility of Al salts and the limited concentrations of the toxic monomeric species which are present in spite of increases in total Al concentration. These toxic species are presumably in the dialyzable fraction of Al which represented 6 to 17% of total lumogallion-reactive Al in media at pH 5.5 and 1 to 10% of total reactive Al at pH 7.O. At pH 5.5, concentration of dialyzable Al was only 67% higher in 1,000 μg/L than in 200 μg/L Al media. Lack of Al toxicity at pH 7.0 may be explained by changes in Al species to less toxic species and/or the apparent lower solubility of A1C1₃ in the Precambrian Shield lake water at pH 7.0 than at 5.5. Aluminum toxicity constitutes a small additional stress to moltingO. virilis in softwater lakes acidified to between pH 6.0 and 5.0 which have elevated Al levels. In this pH range, natural populations ofO. virilis subject to acidification fail, apparently because of difficulties of ionic regulation coupled with other factors.