Canadian Water Quality Guidelines for the Protection of Aquatic Life - Aluminium (Withdrawn)

Aluminium (Al; CAS # 7429-90-5; molecular weight 26.98) is a silvery-white, pliable metal usually found in compounds as Al³⁺ (WHO 1997). It is the most abundant metal in the earth's crust, and the third most common element (Sparling and Lowe 1996). Aluminium is very light (density = 2.70 g-cm^-3), capable of being hammered, cast, drawn out, machined, and moulded, and is therefore easily formed into many shapes (Frank et al. 1985, as cited in WHO 1997). Aluminium is found in a variety of minerals, usually combined with elements such as silicon, oxygen, phosphates, fluorine, and hydroxides, to name a few (Lide 1991, as cited in WHO 1997; Frank et al. 1985; Hudson et al. 1985).

With an annual production in excess of two million tonnes, Canada ranks third in the world in total aluminium metal production. The top primary aluminium producers in Canada are located in Quebec, except for Alcan's Kitimat smelter in British Columbia, and include Alcan Aluminium Limited, Canadian Reynolds Metals Company Limited, Aluminerie de Becancour Inc. (A.B.I), Aluminerie Lauralco Inc., and Aluminerie Alouette Inc. (A.A.I) (Aluminium Association of Canada 1993). Alcan now owns and operates thirteen aluminium smelters with an annual rated capacity of 1589 kilotonnes/year including 1118 kilotonnes from its seven Canadian aluminium smelters (Alcan Aluminium Ltd. 1998). Canadian Reynolds Metals Company Limited, A.B.I, Aluminerie Lauralco Inc., and A.A.I have annual production capacities for primary aluminium of 400, 360, 215, and 215 kilotonnes, respectively (Aluminium Association of Canada 1993).

Aluminium metal has many desirable characteristics for the manufacturing of consumer products (Lide 1991, as cited in WHO 1997; Sax and Lewis 1987). It is used extensively in the making of containers in the food and beverage industry. It has high electrical conductivity, is resistant to corrosion, is light, and recyclable (Aluminium Association Inc. 1998a,b; WHO 1997). Aluminium metal is used as a design material for building and construction; for rod, cable and wire products in the electrical industry; for the production of metal alloys; and for components in the transportation industry (e.g., automobiles and aircraft). Other aluminium products include jewellery, road signs, cooking utensils, foil for household and commercial packaging, decorations, and corrosion-resistant chemical equipment (Aluminium Association of Canada 1993; ATSDR 1992, as cited in WHO 1997). Several aluminium salts have been identified as being of particular concern to the Canadian environment (Germain et al. 1999). These salts include aluminium chloride, aluminium sulphate and aluminium nitrate. Aluminium chloride is used in its anhydrous form in the manufacture of rubbers and lubricants. In its hydrated form it can be used for wood preservation, the manufacture of cosmetics and deodor-ants, or as a disinfectant in slaughterhouses. Aluminium sulphate (alum) is used in many water treatment plants in Canada as a coagulant to help remove nutrients (i.e., phosphorus) from water and help prevent or reduce eutrophication (Germain et al. 1999; Health Canada 1994; Lamb and Bailey 1981). Aluminium polymers (i.e., poly-aluminium sulphate and poly-aluminium chloride) may also be used in water treatment. Aluminium sulphate is also used as a mordant in dyeing, in the leather industry, in the paper industry, in fire-proofing and waterproofing textiles, and in antiperspirants and pesticides among other uses. Aluminium nitrate is used in antiperspirants, as a corrosion inhibitor, as a chemical reagent and in the leather tanning industry (Germain et al. 1999).

The study of the environmental chemistry of aluminium has been restricted by the inability to differentiate between aqueous and particulate Al, and between inorganic and organic forms of aqueous Al (Driscoll and Postek 1996; Driscoll and Schecher 1990). Measurements of aluminium in water are made using a wide variety of analytical methods, with varying extraction periods and digestion procedures. This makes it difficult to compare Al values between studies due to the uncertainty between measured values using different methods, and the type of aluminium reported by the authors (e.g., total aluminium (Al_tot), inorganic monomeric aluminium (Al_im), organic monomeric aluminium (Al_om), and dissolved aluminium (Al_d)). For the purposes of these guidelines total aluminium represents all of the forms of dissolved and undissolved aluminium in water and is often determined in nonfiltered samples (Driscoll and Schecher 1990). Al_tot is the most commonly reported form due to the low cost and ease of analysis of samples (Germain et al. 1999). Monomeric aluminium comprises a single ion of aluminium (Al³⁺) that most often is linked to other compounds as a ligand, that is either organic or inorganic. Dissolved aluminium is commonly defined as the fraction of aluminium present in a sample filtered through a 0.45 μm membrane (Germain et al. 1999). Colloidal aluminium, aluminium bound with soluble organic ligands, and monomeric aluminium are constituents of the dissolved aluminium fraction.

Analytical methods have been developed to determine the concentration of aluminium in many environmental samples (Bloom and Erich 1996). A thorough review of the common methods for determining aluminium in water is described in 'Standard Methods for the Examination of Water and Wastewater' (APHA et al. 1995). The most common methods include the graphite furnace atomic emission spectrometric method (detection limit 0.003 mg-L^-1), the inductively coupled plasma atomic emission spectrometric method (detection limit 0.04 mg-L^-1), and many UV-visible spectrophotometry methods that involve reacting aluminium with a specific reagent (e.g., catechol method).

The fate and behaviour of aluminium in the environment is very complex. Aluminium speciation and solubility are affected by a wide variety of environmental parameters including pH, temperature, dissolved organic carbon (DOC), and numerous ligands (e.g., F^-). Of primary importance to understanding aluminium fate and behaviour are its interactions with pH (Berntssen et al. 1997; DeLonay et al. 1993; Howells et al. 1990; OMOE 1988; Schindler 1988; Hutchinson and Sprague 1987; Burton and Allen 1986; Campbell and Stokes 1985; Clark and Hall 1985; Clark and LaZerte 1985; Baker and Schofield 1982) and dissolved organic carbon (DOC) (Kullberg et al. 1993; Simonin et al. 1993; Peterson et al. 1989; Hutchinson and Sprague 1987; Lacroix and Townsend 1987; Parkhurst 1987).

Both the solubility and speciation of aluminium are pH dependent (Driscoll and Postek 1996; Howells et al. 1990; Spry and Wiener, 1991). Aluminium is a strongly hydrolyzing metal and is relatively insoluble in the neutral pH range (6.0 - 8.0). In the presence of complexing ligands and under acidic and alkaline conditions (pH <6 or >8), aluminium solubility is enhanced. At low pH values, dissolved Al is present in the aquo form (Al³⁺). Hydrolysis occurs as pH rises resulting in a series of less soluble hydroxide complexes (e.g., Al(OH)²⁺, Al(OH)₂⁺). Aluminium solubility is at aminimum near pH 6.5 at 20°C and then increases as the anion, Al(OH)₄^- begins to form at higher pH (Witters et al. 1996; Driscoll and Schecher 1990; Howells et al. 1990). Ambient temperature will also have an impact on aluminium speciation and hence solubility in the environment (Lydersen et al. 1990). At low temperature (2°C), aluminium species are expected to remain in their most toxic form (Al_im) at a higher pH than would occur at higher temperature (20°C) (Howells et al. 1990; Lydersen et al. 1990). Thus at 2°C and pH < 5.7, aluminium is primarily present in the form Al⁺³ and Al(OH)⁺². In the pH range 5.7 - 6.7, aluminium hydroxide species dominate, including Al(OH)⁺² and Al(OH)₂⁺. In this range, aluminium solubility is low and availability to aquatic biota should also be low. At pH >6.7, Al(OH) -4- becomes the dominant species (Howells et al. 1990). This shift in speciation due to temperature can have an impact on the toxicity of aluminium to aquatic organisms (Howells et al. 1990).

Dissolved organic carbon (DOC) is defined as the chemically reactive organic fraction of the organic carbon pool dissolved in water that passes through a 0.45 μm glass fibre filter (Rand et al. 1995). Dissolved organic carbon originates in the terrestrial ecosystem as by-products of biodegradation and chemical agents in the cycling of nutrients and natural weathering (Kullberg et al. 1993). In natural waters, DOC is comprised of a number of organic compounds the majority of which are humic acids (~50-75%) (Kullberg et al. 1993). Humic substances are ubiquitous components of freshwater and their concentrations vary widely (Hutchinson and Sprague 1987). DOC concentrations range from 1-4 mg-L^-1 in oligotrophic and mesotrophic lakes, 2-10 mg-L^-1 in large rivers, 3-34 mg-L^-1 in eutrophic lakes, and 20-50 mg-L^-1 in dystrophic lakes (Rand et al. 1995). The Ontario Acid Sensitivity Database contains water chemistry data for about 6000 Ontario lakes (Neary et al. 1990, in Spry and Weiner 1991). Those Ontario lakes with pH above 5.3 typically had DOC levels greater than 1 mg-L^-1, and DOC concentrations in most were considerably higher. DOC will complex aluminium in water forming organo-aluminium complexes and reducing concentrations of monomeric forms of aluminium (Parent et al. 1996; Farag et al. 1993; Howells et al. 1990). At pH 4.5, 1 mg-L^-1 of DOC can complex approximately 0.025 mg-L^-1 of aluminium with its complexing capacity increasing as pH increases (OMOE 1988).

There are two general types of ligands that can form strong complexes with aluminium in solution. Inorganic ligands include anions such as sulphate (SO₄^2-), fluoride (F^-), phosphates (PO₃^3-), bicarbonates (HCO₃^-), or hydroxides (OH^-), among others. Organic ligands include oxalic, humic or fulvic acids (Sparling and Lowe 1996; Driscoll et al. 1980). The relative concentrations of the inorganic or organic ligands will determine which type of ligand is formed in solution.

Several recent review documents have further information on the behaviour and toxicity of aluminium in the aquatic environment (Phippen and Horvath 1998; Roy 1998; Valcin 1998; WHO 1997; Sparling and Lowe 1996; Howells et al. 1990).

Aluminium in the aquatic environment comes from both natural and anthropogenic sources. The National Pollutant Release Inventory (NPRI) summary report for 1996 reports total on-site industrial aluminium releases for Canada of 52.4 tonnes, with 18.7 tonnes released to the air, 12.8 tonnes into water, and 17.3 tonnes to land (NPRI 1996). As aluminium makes up roughly 8.1% of the earth's crust, the amount of aluminium found naturally in the environment exceeds aluminium from anthropogenic sources (Lantzy and Mackenzie 1979, as cited in WHO 1997). Direct anthropogenic releases that impact the aquatic environment include soil-derived dusts from activities such as farming, mining, and coal combustion where aluminium is highly concentrated (WHO 1997; Havas and Jaworski 1986). Wind and water erosion from agricultural lands is a particularly important source of aluminium in the aquatic environment (WHO 1997). Aluminium can be transported in the form of particulates in the atmosphere and deposited through both wet and dry deposition. Aluminium conc-entrations in precipitation are usually low (< 2 mg-L^-1) but can be increased markedly when influenced by industrial sources (e.g., ore smelting, coal combustion) or natural particulate sources (e.g., soil transport) (Havas and Jaworski 1986). Aluminium may be indirectly mobilised or made more bioavailable due to emissions of acidifying substances such as nitrogen oxides and sulphur dioxide to the atmosphere. These substances when deposited as acid rain lower environmental pH thereby making aluminium more soluble and altering aluminium speciation.

Between 1990 and 1996 aluminium levels in water were measured in Canada near industries using and releasing aluminium salts and other forms of aluminium. In Manitoba, mean extractable aluminium levels ranged from 0.232 mg-L^-1 in South Indian Lake to 0.547 mg-L^-1 in the Burntwood River, and average dissolved aluminium measured in the Burntwood River was 0.06 mg-L^-1. In Saskatchewan, the average mean levels of total aluminium ranged from 0.32 mg-L^-1 in the South Saskatchewan River to 2.15 mg-L^-1 in the North Saskatchewan River. In Ontario, total aluminium levels were highest in Kaministiquia River near Thunder Bay with concentrations reaching up to 13 mg-L^-1, and the highest mean total aluminium levels reached 1.3 mg-L^-1 in the Wabigoon River, downstream of Dryden. Lower levels of total aluminium in Ontario were measured in Lake Superior with a maximum concentration of 0.002 mg-L^-1. Dissolved aluminium levels ranged from 0.44 to 0.058 mg-L^-1 in the St. Clair River. In Quebec, mean total aluminium levels ranged from 0.07 in the St. Maurice River to 0.59 mg-L^-1 in the St. Lawrence River (Germain et al. 1999).