A Laboratory Study of the Effects of Aluminum and pH on Amphibian Eggs and Tadpoles

Abstract

Bufo americanus and Rana sylvatica eggs and tadpoles were exposed in laboratory bioassays to a range of pH and aluminum concentrations commonly encountered in ponds and streams of central Ontario. Bufo americanus and R. sylvatica hatching success was reduced at pH 4.14. The addition of 10 μg inorganic monomeric aluminum (IMAl)/L at pH < 4.35 further reduced hatching success of B. americanus. Rana sylvatica was slightly less sensitive, with hatching success being reduced by addition of 20 μg IMAl/L at pH 4.14. Increasing aluminum concentrations at pH 4.14 appeared to have no further effect except at the highest level used (200 μg/L). IMAI that was toxic at pH 4.35 or 4.14 had no effect at pH 4.75 or 5.75. Toxicity was not dependent on the aluminum speciation, since similar levels of Al3+ and Al(OH)x complexes that were toxic at pH 4.14 were not toxic at pH 4.75; also, Al(F)x complexes were as toxic as Al3+. Egg mortality due to hydrogen ion stress was correlated with a delay in time of hatch and a reduction in egg size; however, there was no consistent pattern with respect to aluminum stress. Bufo americanus and R. sylvatica tadpoles were not sensitive to up to 200 μg IMAl/L and pH as low as 4.14.