Influence of acidic to basic water pH and natural organic matter on aluminum accumulation by gills of rainbow trout (Oncorhynchus mykiss)

Abstract

Juvenile rainbow trout (Oncorhynchus mykiss) (∼0.6 g) were exposed to 3 µmol Al·L–1 in ion-poor water adjusted to pH 4–10 in the absence or presence of natural organic matter (NOM). Aluminum accumulation by trout gills was highest at pH 6–8, there was moderate Al accumulation by trout gills at pH 5 and 9, and trout at pH 4 and 10 did not accumulate any Al on their gills. NOM at 5 mg C·L–1 eliminated Al accumulation by trout gills at all water pHs. These results are explained by NOM complexing Al and keeping Al in solution but off the gills, by H+ competition with Al3+ at low pH, by poor binding of the Al(OH)4– anion to negatively charged gills at high pH, and by polymerization and precipitation of Al onto the gills at intermediate water pH, especially if water pH in the gill micro environment is considered. Increased fish mortality at pH 10 in the presence of NOM is explained by the indirect effect of NOM tying up the limited amount of Ca in the ion-poor water.