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To place a proper perspective on the assessment of aluminium in soils we quote the Executive Summary of the USEPA EcoSSL (Ecological Soil Screening Level) assessment for aluminium.

 

SUMMARY OF ECO-SSLs FOR ALUMINUM

"Aluminum (Al) is the most commonly occurring metallic element, comprising eight percent of the earth's crust (Press and Siever, 1974). It is a major component of almost all common inorganic soil particles, with the exceptions of quartz sand, chert fragments, and

ferromanganiferous concretions. The typical range of aluminum in soils is from 1 percent to 30 percent (10,000 to 300,000 mg Al kg-1) (Lindsay, 1979 and Dragun, 1988), with naturally

occurring concentrations varying over several orders of magnitude.

EPA recognizes that due to the ubiquitous nature of aluminum, the natural variability of aluminum soil concentrations and the availability of conservative soil screening benchmarks (Efroymson, 1997a; 1997b), aluminum is often identified as a COPC for ecological risk assessments. The commonly used soil screening benchmarks (Efroymson, 1997a; 1997b) are based on laboratory toxicity testing using an aluminum solution that is added to test soils.

Comparisons of total aluminum concentrations in soil samples to soluble aluminum-based screening values are deemed by EPA to be inappropriate. The standard analytical measurement of aluminum in soils under CERCLA contract laboratory procedures (CLP) is total recoverable metal. The available data on the environmental chemistry and toxicity of aluminum in soil to plants, soil invertebrates, mammals and birds as summarized in this document support the following conclusions:

• Total aluminum in soil is not correlated with toxicity to the tested plants and soil invertebrates.

• Aluminum toxicity is associated with soluble aluminum.

• Soluble aluminum and not total aluminum is associated with the uptake and bioaccumulation of aluminum from soils into plants.

• The oral toxicity of aluminum compounds in soil is dependent upon the chemical form (Storer and Nelson, 1968). Insoluble aluminum compounds such as aluminum oxides are considerably less toxic compared to the soluble forms (aluminum chloride, nitrate, acetate, and sulfate). For example, Storer and Nelson (1968) observed no toxicity to the chick at up to 1.6% of the diet as aluminum oxide compared to 80 to 100% mortality in chicks fed soluble forms at 0.5% of the diet.

 

Because the measurement of total aluminum in soils is not considered suitable or reliable for the prediction of potential toxicity and bioaccumulation, an alternative procedure is recommended for screening aluminum in soils. The procedure is intended as a practical approach for determining if aluminum in site soils could pose a potential risk to ecological receptors. This alternative procedure replaces the derivation of numeric Eco-SSL values for aluminum."

 

References:

Efroymson, R.A., M.E. Will, and G.W. Suter II, 1997a, Toxicological Benchmarks for Potential Contaminants of Concern for Effects on Soil and Litter Invertebrates and Heterotrophic Process, ES/ER/TM-126/R2, Oak Ridge National Laboratory, Oak Ridge, TN.

 

Efroymson, R.A., M.E. Will, G.W. Suter II, and A.C. Wooten, 1997b, Toxicological Benchmarks for Screening Contaminants of Potential Concern for Effects on Terrestrial Plants: 1997 Revision, ES/ER/TM-85/R3, Oak Ridge National Laboratory, Oak Ridge, TN.

 

Dragun, 1988. The Soil Chemistry of Hazardous Materials. Hazardous Materials Control Research Institute. Silver Spring, MD USA.

 

Lindsay, W.L. 1979. Chemical Equilibria in Soils. John Wiley & Sons,.

 

Press, F. and R. Siever. 1974. Earth. W. H. Freeman and Co.,.

Storer N.L., Nelson T.S. 1968 The effect of various aluminum compounds on chick performance. Poult Sci.Jan; 47(1):244-7.