Standard Test Method for Bioavailable Aluminum in Water with Suspended Solids

Importancia y uso:

5.1 Recent research results investigating the relationship between water chemistry and aluminum toxicity to aquatic organisms are available. Toxicity was shown to vary as a function of pH, dissolved organic carbon (DOC), and hardness. Biological responses in toxicity tests do not correlate with dissolved metal because in circumneutral waters (pH 6 to 8.5) aluminum occurs as a hydroxide species or mineral particulate, both of which are removed by filtration. As such, filtration removes some of the metal species responsible for toxicity.

5.2 The U.S. Environmental Protection Agency (EPA) established water quality criteria for aluminum. Many U.S. states have adopted these criteria and require dischargers to meet water quality standards placed in their discharge permit. No direct relationship between dissolved aluminum and toxicity was shown for a wide variety of aquatic organisms in chronic toxicity studies. Toxicity does, however, correlate with aluminum measurements obtained using the pH 4 extraction method.

5.3 Natural water and wastewater frequently contain significant levels of suspended solids (25 mg/L to 300 mg/L) containing minerals high in aluminum. Regulatory authorities typically recommend measurement of total recoverable aluminum, which uses a strong acid and heat digestion. This digestion procedure results in most or all of the inert non-toxic aluminum present in suspended solids being dissolved and the metal reported as “total or total recoverable.”

5.4 The current method (pH 4 extraction) was developed to provide a method that measures aqueous bioavailable aluminum not associated with suspended solids. The data supporting the use of this method to assess toxicity can be found in the publication by Rodriguez et al.4

5.5 The current pH 4 extraction method provides analytical results that are typically greater than the dissolved metal concentration in the same water sample and less than the total recoverable concentration. In water samples with no to very little suspended solids, the pH 4 extracted concentration and the total aluminum concentration are often the same.

5.6 Aluminum salts are frequently used as flocculants in drinking water plants and wastewater treatment plants.

5.7 Aluminum is common in some industrial wastewaters and acid mine (rock) drainage.

Subcomité:

D19.05

Volúmen:

11.01

Palabras clave:

aluminum; analysis; pH 4 extraction; water;