Total Aluminium

There is a great deal of toxicity data available that examines the impact of total aluminium on aquatic biota. A large number of these studies expose biota to aluminium concentrations in artificial exposure solutions where maximum speciation of aluminium will occur and no organic matter is present to complex aluminium. It has been demonstrated that DOC has a large impact on aluminium toxicity by complexing monomeric aluminium (Parent et al. 1996; Farag et al. 1993; Howells et al. 1990). It has also been shown that as DOC concentrations increase in solution, Al toxicity tends to be reduced (Parkhurst 1987; Gunn and Noakes 1987; Burton and Allan 1986). Dissolved organic carbon is a constituent of all natural waters though concentrations vary (Peterson et al. 1989). Due to the impact of DOC on aluminium toxicity, only those studies with measurable DOC as part of the exposure solution are selected for use in deriving the Al_tot water quality guideline for aquatic life.

Parent et al. (1996) examined the impact of aluminium to the green alga, C. pyrenoidosa in the presence of dissolved organic carbon. The DOC concentrations ranged from 1.2-11 mg-L^-1. Total monomeric aluminium concentrations were determined using atomic absorption spectrophotometry with electrothermal atomisation. At pH 5.0, 167 μg-L^-1 of total monomeric aluminium and no DOC resulted in a 30% decrease in growth of green alga over 96 hours relative to the control. When 2.3 mg-L^-1 of DOC and 189 μg-L^-1 Al_tot was added to solution at pH 5.0, growth was reduced by 25% relative to controls.

Hörnström et al. (1995) examined the effect of aluminium at various pH ranges and at two humus concentrations on the phytoplankton Monoraphidium griffithii and Monoraphidium dybowskii. At pH 4.8 and humus concentration 0.2 mg Pt-L-1 a 70% growth reduction was observed relative to controls at 200 μg-L^-1 in M. dybowskii. Humic concentrations are often measured by comparing samples to standard reference solutions of platinum. The humic concentration is then reported in platinum units (mg Pt-L-1). At pH 6.8 and humus concentration 27 mg Pt-L-1, growth reduction was observed at 300 μg-L^-1 aluminium in M. dybowskii. M. griffithii exhibited 82% reduction in growth relative to controls when exposed to 100 μg-L^-1 aluminium at pH 4.8 and humus concentration of 0.2 mg Pt-L-1. At 27 mg Pt-L-1, M. griffithii exposed to 300 μg-L^-1 at pH 4.8 and 6.8 exhibited 35% and 50% growth reduction, respectively.

Freda et al. (1990) exposed R. pipiens embryos and B. americanus tadpoles to levels of aluminium in order to examine the impact of organic complexation on toxicity. Aluminium was measured using spectrophotometry and the catechol-violet method. The test organisms were exposed to various pH and DOC levels with the DOC being derived from natural pond waters. A series of pond water dilutions were used to vary the DOC concentration in the bioassays. The 96-h LC₅₀ for B. americanus tadpoles at a pH of 4.5 and DOC concentration of 2.85 mg-L^-1 was 627 μg-L^-1 total aluminium. Increasing the DOC content to 11.4 mg-L^-1 caused an increase in the LC₅₀ to > 2000 μg-L^-1. R. pipiens embryos exhibited a similar reaction to increasing DOC concentrations. In 100% artificial soft water at pH 4.8 and with no DOC, an LC₅₀ of 471 μg-L^-1 was reported. The LC₅₀s increased markedly (>856 - >1018 μg-L^-1) upon addition of DOC in the form of various pond water dilutions at the same pH.

Freda and McDonald (1990) demonstrated the effects of aluminium to leopard frog (R. pipiens) over a wide range of pH and low DOC. R. pipiens were exposed in a static system rather than flow through in order to better mimic conditions in ephemeral breeding ponds that have no inflow or outflow of water. The authors observed that at very low pH (pH 4.2-4.4) aluminium ameliorated the effects of pH on frog embryos and permitted hatching. Between pH 4.6-4.8 aluminium was found to be extremely toxic with mortality being significantly increased at 500 μg-L^-1. All tests contained a DOC concentration of 1.0 mg-L^-1. The reported 96-h LC₅₀s for Al_tot at 4.6 and 4.8 were 811 and 403 μg-L^-1, respectively. At pH 4.4, 4.6, and 4.8 the lowest concentration of Al tested (250 μg-L^-1) caused either mortality or abnormal deve lopment in pre-stage 25 tadpoles.

It has been suggested that amphibian species most at risk to aluminium toxicity are those that inhabit small temporary or ephemeral ponds that receive most of their water from spring runoff and snow melt (Sparling and Lowe 1996). Albers and Prouty (1987) reported that embryonic survival in spotted salamander Ambystoma maculatum was negatively correlated with the concentration of aluminium in temporary ponds. Aluminium levels and acidity in these waters are particularly high and exposure occurs during early life stages when amphibians tend to be the most sensitive. Larger species that inhabit lakes and permanent ponds may be less at risk from episodic events but can still be affected by chronic acidification and accompanying elevated Al. In a study to determine the effects of a range of Al_tot (250-1000 μg-L^-1) on leopard frog R. pipiens embryos at pH 4.8, Freda (1991) reported that DOC exceeding 5.7 mg-L^-1 complexed most of the Al present, decreasing labile Al.

Aluminium tends to be non-toxic to invertebrates at levels commonly found in circumneutral water. Ambient levels of Al in water at circumneutral pH are usually less than 1 mg-L^-1 and more typically around 500 μg-L^-1 (Wren and Stephenson 1991; Havas and Likens 1985). Burton and Allan (1986) examined the effect of temperature, pH, DOC, and aluminium concentrations on various stream invertebrates. They observed that the addition of 500 μg-L^-1 aluminium to water at 15°C, pH 4.0 and DOC 42-47 mg-L^-1 had no effect on mortality on the isopod, Asellus intermedius, stonefly, Nemoura sp., and the snail Pycnopsyche guttifer relative to a control with no aluminium. At 2°C and with 500 mg-L^-1 Al_tot, significant increased mortality was observed in the stonefly and isopod. Mortality increased when the experiment was repeated at very low DOC levels. The authors observed that the removal of organic matter from the exposure solution resulted in a 94-98% shift of aluminium from organic to inorganic aluminium forms.

Gundersen et al. (1994) exposed rainbow trout (Oncorhynchus mykiss) to acute and subacute combinations of Al, DOC (as humic acid) and pH. Fish were exposed in a continuous flow through exposure system. Aluminium concentrations were measured by absorbance spectrophotometry using the catechol method. In the acute test, humic acid concentrations ranged from 1.4- 10.1 mg-L^-1 and pH was weakly alkaline at 7.97-8.56. The 96-h LC₅₀s were 3.75, 5.43, 4.60, and 5.22 mg-L^-1 at humic acid concentrations of 1.4, 2.6, 6.6, and 10.1 mg-L^-1, respectively. Mortality (25%) was reported at pH 8.03, humic acid concentration of 6.17 mg-L^-1 and a total aluminium concentration of 2.1 mg-L^-1. At the same pH, higher humic acid concentration (9.57 mg-L^-1) and similar Al_tot (1.9 mg-L^-1) mortality was 5%. The authors found that the humic acid protected against aluminium induced mortality.

American flagfish (Jordanella floridae) were used to determine the toxicity of metal mixtures (Al/Cu/Zn) and the impact of humic substances on this toxicity (Hutchinson and Sprague 1987). The authors observed that aluminium toxicity is reduced by complexation with humic substances though the level of toxicity to flagfish was not specifically quantified. Also, total organic carbon was more closely associated with changes in trace metal lethality than changes associated with water hardness.

Peterson et al. (1989) examined the impact of aluminium to Atlantic salmon (S. salar) in the presence of dissolved organic carbon. DOC was isolated from natural stream waters in Nova Scotia and diluted to achieve exposure concentrations. At pH 4.8 and DOC concentration of 4.4 mg-L^-1 Atlantic salmon alevins exhibited 100% mortality at 200 μg-L^-1 (7.4 μm). At pH 4.8 and 6.8 mg-L^-1 DOC, 100% salmon mortality was also exhibited at 210 μg-L^-1 (7.8 μm). The authors suggested that acidic fractions of DOC (i.e., humic acids) are more effective in providing protection to salmon as they contain carboxyl and hydroxyl functional groups that form strong complexes with Al.

Parkhurst et al. (1990) examined the effect of aluminium on brook trout (S. fontinalis) with variable water quality parameters (e.g. pH, DOC, F^- and temperature). The authors used a flow-through system and reported measured as well as nominal parameter concentrations in each bioassay. A multivariate analysis was used to determine which of the parameters were most important to brook trout survival under a wide range of exposure conditions. The authors reported that DOC accounted for 6% of the variability in survival for brook trout. Parkhurst (1987) reported the effect of aluminium on brook trout exposed to Al_tot. Temperature, DOC, and fluoride concentrations were varied. Nominal Al_tot concentrations in the bioassays ranged from 0-1000 μg-L^-1 while measured DOC concentrations ranged from 0.6-9.1 mg-L^-1. Measured values for all parameters were reported. The authors observed that DOC alone had no impact on brook trout survival. Addition of DOC to the various Al_tot bioassays reduced toxicity. At pH 5.3 with 11 μg-L^-1, 21-d survival was 72% with 0.5 mg-L^-1 of DOC. Survival increased substantially with the addition of 5.5 mg-L^-1 DOC to 94%. At 127 μg-L^-1, Al_tot toxicity was virtually eliminated with DOC addition at pH 4.8, 5.1, and 5.4.