Amelioration of behavioural toxicity of aluminium by oligomeric silicic acid and humic acid

Despite its limited solubility at neutral pH, aluminium is significantly accumulated by the freshwater snail Lymnaea stagnalis, leading to behavioral toxicity. Both organic (humic acid) and non-organic (oligomeric silicic acid) ligands have been shown to reduce Al accumulation probably owing to their binding affinity for Al. This study examined the effect of these ligands on behavioral responses to Al over a 30-day exposure period. Both behavioral state score (a measure of general activity) and feeding behaviors were initially (days 2-4) depressed in the presence of 500 µgl-1 added Al, followed by apparent tolerance (days 8-16) and subsequent depression (day 30). In the presence of either oligomeric Si (molar ratio Al:Si 1:40) or humic acid (10 mgl-1) behavioral responses to Al were completely abolished. Neither ligand alone had any effect on behavior except for a slight increase in biting activity in the presence of humic acid on days 2 -4. These results suggest that the presence of complexing ligands may affect toxicity of Al in the natural environment at neutral pH. KEY WORDS: Aluminium, humic acid, silicon, Lymnaea stagnalis, behaviour Egyptian Journal of Biology Vol.3(2) 2001: 56-62