Aluminum toxicity to fish in acidic waters

An important consequence of acidification is the mobilization of Al from the edaphic to the aquatic environment. Elevated Al levels in acidic waters may be toxic to fish. Eggs, larvae, and postlarvae of white suckers (Catostomus commersoni) and brook trout (Salvelinus fontinalis) were exposed in laboratory bioassays to pH levels 4.2 to 5.6 and inorganic Al concentrations of 0 to 0.5 mg l^?1. Aluminum toxicity varied with both pH and life history stage. At low pH levels (4.2 to 4.8), the presence of Al (up 0.2 mg l^?1 for white suckers; 0.5 mg l^?1 for brook trout) was beneficial to egg survival through the eyed stage. In contrast, Al concentrations of 0.1 mg l^?1 (for white suckers) or 0.2 mg l^?1 (for brook trout) and greater resulted in measurable reductions in survival and growth of larvae and postlarvae at all pH levels (4.2 to 5.6). Aluminum was most toxic in over-saturated solutions at pH levels 5.2 to 5.4. The simultaneous increase in Al concentration with elevated acidity must be considered to accurately assess the potential effect of acidification of surface waters on survival of fish populations.