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Studies performed on earthworms using a hydrated salt of aluminium sulphate (and aluminium chloride hexahydrate) in addition to the standard soil containing kaolinite (Al2Si205(OH)) resulted in ecotoxicity at concentrations considerably lower than those found in top- and sub-soils (14 d LC50s around 300 mgAl/Kg dw at pH 3-4 and >1000 mgAl/Kg dw at pH4-6 and 6 week NOECs of 100 mg Al/Kg dw at pH 3.4 -7.3 for reproduction). The observed toxicity could not be related to extractible aluminium concentration as there was no difference between aluminium concentrations extracted from controls and treatments at pH 7.3. There were certain differences between treatment levels such as the addition of CaCO3 which was used to attenuate low soil pH further to aluminium treatment. It is therefore not clear whether the effects found can be directly attributed to aluminium toxicity.

In order to place a more realistic perspective on the assessment of aluminiumin soils we quote the Executive Summary of the USEPA EcoSSL (Ecological Soil Screening Level) assessment for aluminium:

Summary of ECO-SSLs for aluminium

"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 mgAl.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 aluminumin 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 aluminiumfrom 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."

Aluminium,its powders and salts are not classified for the environment. Aluminum (Al) is the most commonly occurring metallic element, comprising eight percent of the earth's crust (Press and Siever, 1974) and is therefore found in great abundance in both the terrestrial and sediment environments. Concentrations of 3 -8% (30,000 -80,000ppm) are not uncommon. The relative contributions of anthropogenic aluminium to the existing natural pools of aluminium in soils and sediments is very small and therefore not relevant either in terms of added amountsor in terms of toxicity. Based on these exposure considerations additional sediment and/or soil testing is not warranted. More information about exposure based waiving for aluminiumin soil and sediments can be found in attached document (White paper on exposure based waiving for Fe and Al in soils and sediments final15-03-2010.pdf).

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 ControlResearch 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. 1968The effect of various aluminum compounds on chick performance. Poult Sci. Jan; 47(1):244-7.