Effect of Fluoride Complexation on Aluminum Toxicity Towards Juvenile Atlantic Salmon (Salmo salar)

In 7-d semistatic bioassays, fluoride complexation attenuated Al toxicity to juvenile Atlantic salmon (Salmo salar; age 1 +) and the accumulation of Al in gill tissue, but not to the extent predicted by the free-ion model of metal toxicity. Bioaccumulation and toxicity persisted even in the presence of an excess of the complexing ligand. An equilibrium model, involving the formation of a mixed ligand complex (F–Al–L-gill) at the gill surface, is proposed to explain this residual toxicity (L-gill = ligand at the gill surface). Exposure to Al, or to a combination of Al and F, led to a decrease in the plasma sodium levels even for sublethal conditions. Aluminum concentrations as low as 2 μM adversely affected the salmon. The similarity of the osmo-regulatory response to the H+-ion, to Al3+, and to Al(F)x suggested that the mechanism of toxicity in the presence of fluoride did not differ markedly from that observed by previous workers for salmonid species exposed to moderately acidic media containing Al but without added fluoride.