Effect of aluminum and silicic acid on the behaviour of the freshwater snail Lymnaea stagnalis

A major factor influencing the toxicity of Al at neutral pH is the presence of complexing ligands. This study compared the effect of exposure to aluminum nitrate, aluminum lactate, and aluminum maltol, in the presence or absence of monomeric silica (Si), on the behaviour of the pond snail Lymnaea stagnalis. Concentrations of Al and Si used were similar to those found in the natural environment. Soluble Al concentration in the water fell significantly with time over 48 h following addition as the nitrate or lactate (500 mu g,L-1), presumably owing to polymerisation as the colloidal hydroxide. This loss was enhanced by the presence of snails or Si (Al:Si = 1:15). Aluminum maltol largely remained in solution. Snails exposed to all three Al compounds showed depression of behavioural activity after 7 days; this effect was ameliorated in the presence of higher (Al:Si = 1:15) but not lower (Al:Si = 1:1) concentrations of Si. Depression of feeding behaviour occurred with all three Al compounds, although it was delayed in the presence of aluminum maltol. Expression of conditioned feeding was inhibited in snails exposed to aluminum nitrate during training and testing. The behavioural changes are likely to be mirrored in the field, with adverse consequences for the "fitness" of natural populations.