Aluminium in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems
Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.
The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Aluminium is the most abundant metallic element in the lithosphere, but has little or no known biological function (Gensemer & Playle 1999).
Summary of factors affecting aluminium toxicity
Toxicity to fish and invertebrates is increased at low (e.g. <5.5) and high pH (e.g. >9).
Toxicity reduced by complexing with fluoride, citrate and humic substances. The effect of organic complexation requires experimental determination.
Toxicity is reduced in presence of silicon.
Toxicity reduced at high water hardness (high calcium concentrations) but no algorithms are currently available.
Increased temperature may increase aluminium toxicity.
No data on salinity effects.
No data on effects of suspended particulate matter.
Toxicity of aluminium may be affected by presence of other metals.
The speciation of aluminium in water can be ascertained using a variety of methods including:
- Analytical techniques, such as physical separation (e.g. [ultra]filtration, dialysis, centrifugation), fluorimetry, potentiometry (e.g. ion-selective electrode), colorimetry, ligand competition, ion exchange and flow-injection (Bloom & Erich 1996, Hawke et al. 1996, Gensemer & Playle 1999, Pyrznska et al. 2000)
- Theoretical techniques, such as geochemical modelling (Browne & Driscoll 1993, Nordstrom & May 1996).
Bioassays are typically used to ascertain metal-organism interactions. These can be coupled with measured and/or predicted speciation calculations to determine the bioavailability of various aluminium species. The current analytical practical quantitation limit (PQL) for aluminium is 0.5 µg/L in both fresh and marine waters (NSW EPA 2000).
Factors affecting bioavailability and toxicity of aluminium
The bioavailability and toxicity of aluminium is generally greatest in acid solutions (Campbell & Stokes 1985). Aluminium in acid habitats has been observed to be toxic to fish (Dillon et al. 1984), amphibians (Andren et al. 1988) and phytoplankton (Folsom et al. 1986, Claesson & Tornqvist 1988). Aluminium is generally more toxic over the pH range 4.4 to 5.4, with a maximum toxicity occurring around pH 5.0 to 5.2 (Schofield & Trojnar 1980, Parent & Campbell 1994). The inorganic single unit aluminium species (A1(OH)2+) is thought to be the most toxic (Driscoll et al. 1980).
Under very acid conditions, the toxic effects of the high H+ concentration appear to be more important than the effects of low concentrations of aluminium; at approximately neutral pH values, the toxicity of aluminium is greatly reduced (CCREM 1987). The solubility of aluminium is also enhanced under alkaline conditions, due to its amphoteric character, and some researchers found that the acute toxicity of aluminium increased from pH 7 to pH 9 (Freeman & Evert 1971, Hunter et al. 1980). However, the opposite relationship was found in other studies (Boyd 1979). There are few studies on toxicity of aluminium in waters of pH >8 (Sparling & Lowe 1996).
Collier and Winterbourne (1987) studied acidic (pH 4.3 to 5.7) and more alkaline (pH 6.6 to 8.0) streams in New Zealand, and found higher numbers of invertebrate taxa (64 compared with 43) and greater mean densities of benthic invertebrates (up to five times higher) in alkaline streams. Although aluminium concentrations in acidic streams were elevated (total reactive aluminium of 123 to 363 µg/L compared with 84 µg/L in alkaline streams), they suggested that the depauperate fauna in those streams was due to changes in the food supply (e.g. epilithon), resulting from pH and not aluminium. However, most of the toxic species of aluminium were probably being complexed by dissolved humic matter in the acidic streams. Initial mixing zones where acidic, aluminium-rich water is neutralised are most toxic to fish (Gensemer & Playle 1999). Fish kills can occur naturally in northern Australia when acidic, Al-rich water is released into billabongs at the end of some dry seasons (Brown et al. 1983).
Poléo et al. (1991) observed an increase in toxicity of aluminium to Atlantic salmon with increasing temperature, which may be due to faster aluminium polymerisation at higher temperature, as well as higher metabolic rate of the fish. Temperature also affects aluminium speciation and solubility (Gensemer & Playle 1999).
The uptake and toxicity of aluminium in freshwater organisms generally decreases with increasing water hardness under acidic, neutral and alkaline conditions (Folsom et al. 1986, Playle et al. 1989, Reid & McDonald 1991, Gunderson et al. 1994). Hutchinson and Sprague (1987) found that the threshold toxicity of aluminium to flagfish Jordanella floridae (95 µg/L in soft water at pH 5.8) was reduced to 29 µg/L in the presence of zinc (5 µg/L) and copper (2 µg/L). Gensemer and Playle (1999) outline the complexity of mixture effects with aluminium.
Complexing agents such as fluoride, citrate and humic substances reduce the availability of aluminium to organisms, resulting in lower toxicity. Silicon can also reduce aluminium toxicity to fish (Gensemer & Playle 1999).
No studies have reported the effect of salinity on the uptake and toxicity of aluminium to estuarine and marine organisms. Further, no information on the bioavailability of aluminium sorbed to colloidal and particulate matter has been reported.
Toxicity and freshwater guidelines for aluminium
Gensemer and Playle (1999) provide a detailed summary of aluminium toxicity to various aquatic organisms. Among freshwater aquatic plants, single-celled plants are generally the most sensitive to aluminium (USEPA 1988a). Fish are generally more sensitive to aluminium than aquatic invertebrates (Gensemer & Playle 1999). Aluminium is a gill toxicant to fish, causing both ionoregulatory and respiratory effects (Gensemer & Playle 1999). Aluminium is more toxic in both acidic and alkaline water. Clark and LaZerte (1985) reported that hatching success of American toad Bufo americanus at pH 4.3 was significantly reduced with addition at 10 mg/L aluminium and the NOEC was 5 µg/L. CCREM (1987) considered that concentrations greater than 100 mg/L would be deleterious to aquatic life at pH >6.5.
Screened freshwater toxicity data for aluminium were separated into those conducted at pH >6.5 and those at pH <6.5. Acute and chronic toxicity data are outlined below but only acute data were used for calculations. Chronic toxicity figures comprised a mixture of LC/EC50, LOEC, MATC and NOEC figures; where stated, these were converted to NOEC equivalents using the method modified from van de Plassche et al. (1993) (ANZECC & ARMCANZ 2000 Section 184.108.40.206) (expressed mostly as geometric means for species). The pH range was 6.5 to 8.6.
Freshwater pH >6.5
Fish: Acute 48 to 96-hour LC50 five species: 600 (Salmo salar) — 106,000 mg/L; chronic seven species, 8 to 28-day converted NOEC, 34 to 7100 µg/L. The lowest measured chronic figure was an 8-day LC50 of 170 µg/L for Micropterus sp.
Amphibian: Acute Bufo americanus, 4-day LC50 860 to 1660 µg/L; chronic, 8-day LC50 of 2280 µg/L.
Crustaceans: one species 48-h LC50 2300 to 36,900 µg/L; chronic three species, 7 to 28-day NOEC, 136 to 1720 µg/L.
Algae: 96-h EC50 population growth, 460 to 570 µg/L; chronic two species, NOEC, 800 to 2000 µg/L.
Freshwater pH <6.5 (all between pH 4.5 and 6.0)
Fish: four species, 24–96h LC50 15 (S. trutta) — 4200 µg/L; chronic data on S. trutta, 21 to 42-day LC50, 15 to 105 µg/L.
Amphibians: two species, 4 to 5-day LC50 540 to 2670 µg/L (absolute range 400 to 5200 µg/L).
Alga: one species NOEC growth 2000 µg/L.
A freshwater moderate reliability trigger value of 55 µg/L was derived for aluminium at pH >6.5 using the statistical distribution method (Burr distribution as modified by CSIRO, ANZECC & ARMCANZ 2000 Section 220.127.116.11) with 95% protection and an ACR of 8.2. A freshwater low reliability trigger value of 0.8 µg/L was derived for aluminium at pH <6.5 using an assessment factor (AF) of 20 (essential element) on the low pH trout LC50 figure. The low reliability figures should only be used as indicative interim working levels.
A total of 11 acute data points were available for aluminium in seawater, comprising three taxonomic groups, as follows:
Crustaceans: four species, 72 to 96-hour LC50, 240 µg/L (Balanus eburneus) to 10,000 µg/L (Nitocra spinipes); a 7-day NOEC (mortality) for Cancer anthonyi of 1000 µg/L.
Mollusc: one species, 72-hour LC50, 2440 µg/L.
Annelid: two species, 96-hour LC50, 97 µg/L (Ctenodrilus serratus) to 405 µg/L (Capitella capitata).
There was an insufficient spread of data to calculate a reliable guideline trigger value for aluminium in seawater.
There were limited marine data and procedures for calculating an Environmental Concern Level (ECL) (ANZECC & ARMCANZ 2000 Section 18.104.22.168) were used to calculate a low reliability marine trigger value of 0.5 µg/L derived for aluminium using an AF of 200. This figure should only be used as an indicative interim working level but could be revisited as more data become available. The factor of 200 was used because the ECL factor of 1000 was considered excessive for such a commonly found element.
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