Scientific criteria document for development of Provincial Water Quality Objectives and Guidelines: Aluminum
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Several sources of aluminum account for ambient concentrations in aquatic ecosystems in Ontario. These include natural sources resulting from mineral weathering, as well as anthropogenic sources such as industrial processing, and alum treatment of water for drinking, sewage treatment and pulp and paper processing. Aluminum can combine with a number of organic and inorganic anions to form simple complexes or very large complex molecules in suspension. The dominant forms of aluminum found in a given waterbody will be a function of the competing anions and aquatic parameters such as pH, alkalinity, hardness, and DOC. pH and DOC have been identified as the most significant parameters governing the behaviour of aluminum ions in solution. The nature of the aluminum ion complex will influence aquatic toxicity. Analytical procedures can now identify and measure some forms of aluminum that are toxic to aquatic life in low pH regimes. Inorganic aluminum, particularly inorganic monomeric aluminium (IMAL), is the form considered to be most toxic in acid stressed environments, organic aluminum being relatively non toxic. However, at mildly acidic pH values where aluminum solubility is minimal, supersaturated solutions of inorganic aluminum also appear to be toxic. At pH values greater than 6.5 the toxic forms of aluminum have not been identified. The organic and inorganic forms of aluminum are difficult to separate by current routine analytical procedures. Toxicological information from a wide range of laboratory and field studies has been assessed for use in this report. Although there is a large amount of information available for total aluminum toxicity in a wide variety of species, relevant data for the pH range 4.5 to 6.5 showing toxicity of inorganic aluminum alone are almost entirely from studies on fish. Data from a broader spectrum of species have been used in the pH range 6.5 to 9.5. Three Provincial Water Quality Guidelines have been developed for aquatic environments with pH values from 4.5 to 9.0. Two are numerical guidelines, one is narrative. All are intended for samples free of any clay fraction (see Appendix I for analytical procedures). These guidelines are for the protection of all forms of aquatic life, recreational purposes, and aesthetic values. They are not drinking water guidelines.