Canadian Water Quality Guidelines for the Protection of Aquatic Life - Aluminium (Withdrawn)

There are few studies available on the toxicity of Al_im to aquatic biota. In particular, studies on plants and invertebrates are rare. This is likely the result of the difficulty in finding accurate and precise analytical methods to determine the concentrations of Al_im in solution (Driscoll and Postek 1996; Driscoll and Schecher 1990). Additionally, the toxicity of Al_im to aquatic organisms can be difficult to quantify at low pH due to the inherent toxicity of the H⁺ ion (Baldigo and Murdoch 1997; Atland and Barlup 1996; Parkhurst et al. 1990). In nature, species sensitive to low pH toxicity would not be expected to inhabit aquatic systems where acidic conditions predominate. For the purposes on this guideline, only those studies that report the toxic effects of Al_im relative to proper controls at the same exposure pH are reported.

Aquatic Plants

Parent and Campbell (1994) exposed the unicellular green algae (Chlorella pyrenoidosa) to Al_im to observe biological responses at various pH levels. Algal growth inhibition was minor at pH 4.3-4.6. The EC₃₀s for algal growth were calculated to range from 7-800 μg-L^-1 for pH 6.0-5.0. The most sensitive EC₃₀ was reported at pH 6.0 and 7 μg-L^-1 Al_im. Toxicity was extremely dependent on pH in this range. Both Parent and Campbell (1994) and Parker et al. (1989, in Lydersen et al. 1990) have suggested that poly-nuclear hydroxyl aluminium species may have pronounced phytotoxic effects. These Al species are expected to be present at pH ranging from 5 - 7 depending upon temperature and other physical chemical factors (e.g., ligands).

Invertebrates

Mackie (1989) exposed five benthic invertebrates to six levels of Al_im ranging from 0-400 μg-L^-1 and pH ranging from 4-5.5. The test species included the shredder, Hyalella azteca, the scraper, Amnicola limosa, the predator, Enallagma sp., and the bivalves Pisidium casertanum and Pisidium compressum. The invertebrates were exposed, in static test systems, to Al_im for 96-h to determine the LC₅₀ at each exposure concentration. Insufficient mortality was observed to calculate LC₅₀ values at the concentrations tested.

Khangarot and Ray (1989) examined the toxicity of various metals as ions (Al³⁺) and the correlation to their physicochemical properties to the water flea, Daphnia magna. Static bioassay tests at 13°C, were used to determine the toxicity of the test metals. The 24-h EC₅₀ and 48-h EC₅₀ were reported as 85.9 mg-L^-1 and 59.6 mg-L^-1, respectively.

Amphibians

Clark and LaZerte (1985) examined the effects of pH and aluminium on eggs and tadpoles of American toad (Bufo americanus) and wood frog (Rana sylvatica). They found that at low pH (i.e., 4.14), hatching success for eggs of both species were significantly reduced. Reproductive success at pH 4.32 with the addition of 9.2 μg-L^-1 Al_im was reduced in the American toad. With the addition of up to 200 μg-L^-1 of Al_im at pH 4.75, there was no change in hatching success. Below pH 4.75, aluminium was found to augment toxicity due to pH. Similar results have been reported for other amphibian species at different life stages (Freda 1991; Saber and Dunson 1979; Gosner and Black 1957). The sensitive endpoint at 9.2 μg-L^-1 was not selected for guideline development due to the presence of large effects due to pH alone in the bioassay. The authors concluded that toxic response was not dependent on aluminium speciation (Clark and LaZerte 1985).

Fish

Mount et al. (1988) exposed brook trout (Salvelinus fontinalis) to monomeric aluminium in low calcium (0.5 mg-L^-1) and low pH (4.97 ± 0.02) conditions. Al uminium was reported as both inorganic and total monomeric. The lowest observed effect concentration (LOEC) for growth was reported as 47 μg-L^-1 Al_im. Total monomeric aluminium was 169 μg-L^-1. The observed effects ranged from reduced growth and survival to physiological abnormalities. The authors observed that raising the calcium concentrations or lowering the aluminium concentration alleviated the observed adverse responses.

Holtz and Hutchinson (1989) exposed fish species at various life stages to solutions with low pH (ranging from pH 4.5 to 6.0) and concentrations of Al_im. Survival of lake whitefish (Coregonus clupeaformis) swim-up fry was found to be the most sensitive endpoint with a reported LOEC of 28 μg-L^-1 at pH 5.1. The LOEC for survival in smallmouth bass (Micropterus dolomieui) swim-up fry at pH 5.1 was 144 μg-L^-1 and at pH 5.4, >58 μg-L^-1. At pH 5.97, common shiner (Notropis cornutus) eggs exhibited 90.7% mortality at an Al_im concentration of 17 μg-L^-1. This sensitive endpoint was not selected for guideline derivation. The authors suggested that the toxicity reported at this sensitive endpoint was due to aluminium over-saturation. The authors measured colloidal and polymeric aluminium in the test solutions and determined that these were less important than acidity and Al_im concentrations to fish survival.

Roy and Campbell (1995) exposed juvenile Atlantic salmon (Salmo salar) to concentrations of aluminium (as Al_im) and aluminium and zinc mixtures over a wide pH range. The most sensitive response to Al_im alone, occurred at pH 5.24. The reported LC₅₀ was 51.2 μg-L^-1 (1.9 μmol). The authors found that the LC₅₀s tended to be lower in the aluminium and zinc mixture bioassays then with just aluminium alone. Aluminium acted as a gill irritant that stimulated mucus production in the salmon. Zinc readily binds to gill mucus and can cause a rapid influx of metal ions through the gill tissue resulting in a toxic response.