Aluminium sodium dioxide

Sediment toxicity

Additional information

In water (including soil or sediment pore water), NaOH is present as the sodium ion (Na+) and hydroxyl ion (OH-), as solid NaOH rapidly dissolves and subsequently dissociates in water. If emitted to surface water, sorption to particulate matter and sediment will be negligible.

Due to its chemical nature sodium aluminate is not stable under natural environmental conditions. The main degradation products are sodium hydroxide and various aluminium species subject to the prevailing environmental conditions, for instance pH regime.

The environmental fate of sodium hydroxide was addressed in a risk assessment report by the European Union (2007). In water (including soil or sediment pore water), NaOH is present as the sodium ion (Na+) and hydroxyl ion (OH-), as solid NaOH rapidly dissolves and subsequently dissociates in water. If emitted to surface water, sorption to particulate matter and sediment will be negligible.

The relevant compound to consider with regard to sediment toxicity of sodium aluminate is aluminium. The environmental chemistry of aluminium is complex and was addressed in several reports and public available sources to date (e.g. Sposito 1995, WHO 1997, EURAS 2007). Aluminium is the most abundant metallic element in the Earth's crust, with a proportion of around 8% by weight, and the third most abundant of all elements. Due to its reactive nature it does not exist as free elemental metal, rather it occurs in hundreds of different compounds and minerals. Against the background of this abundance and taking into account available data on the anthropogenic input to the terrestrial environment it is reasoned that aluminium from anthropogenic sources is negligible, both in terms of added amounts as well as in terms of toxicity. Vangheluwe et al (2010) investigated in detail the relative anthropogenic contribution to the existing natural pool. The assessment by Vangheluwe et al (2010) is based on aluminium concentrations for Europe, collected fromFOREGS’ geochemical baseline program database (Salminen et al. 2005, http://www.gsf.fi/publ/foregsatlas/index.php), that provides high quality environmental geochemical baseline data for Europe based on samples of stream water, stream sediment, floodplain sediment, soil and humus. For aluminium oxide concentrations of 10.5 % in topsoil, 11.3 % in subsoil, 9.8 % in stream sediment, and 10.1 % in floodplain sediment are reported. The relative importance of anthropogenic contributions of aluminium to the natural background in soil and sediments were evaluated by use of the exposure model EUSES. For the calculation of regional sediment and soil concentrations of aluminium the model was fed with the following emission data. The alumina and primary aluminium production in the European Union is estimated to be about 11.8 million tonnes of aluminium oxide. Aluminium partitioning data (log Kd values) are 5.2 for sediment and 6.62 for suspended particulate matter (SPM). Kd values for aluminium for soil are not available and as a rough estimate the soil Kd was also used for the sediment compartment.

Emission of aluminium oxide to air from alumina plants is estimated to be 10,564 tonnes. Releases to water are very limited. Removal rate in sewage treatment plants is assumed to be 80 %. The modeling exercise resulted in a relative anthropogenic aluminium contribution to topsoil and stream sediment of 0.2 and 0.17 %, respectively. The assessment by Vangheluwe et al (2010) therefore demonstrates, that the natural background concentration far outweighs anthropogenic contribution and exposure based waiving is justified for aluminium.

 

EURAS (2007) Development of a high quality aquatic ecotoxicity database for Al metal, Al oxide and Al hydroxide.

European Union (2007) European Union Risk Assessment Report. Sodium hydroxide. CAS 1310-73-2. EINECS No. 215-185-5. Targeted Risk Assessment.

Salminen, R., Batista, M.J., Bidovec, M., Demetriades, A., De Vivo, B., De Vos, W., Duris, M.,Gilucis, A., Gregorauskiene, V., Halamic, J., Heitzmann, P., Lima, A., Jordan, G., Klaver, G., Klein, P., Lis, J., Locutura, J., Marsina, K., Mazreku, A., O'Connor, P.J., Olsson, S.Å., Ottesen, R.-T., Petersell, V., Plant, J.A., Reeder, S., Salpeteur, I., Sandström, H., Siewers, U., Steenfelt, A., Tarvainen, T. (2005) Geochemical Atlas of Europe. Part 1 - Background Information, Methodology and Maps.

Sposito (ed) (1995) The environmental chemistry of aluminium. Crc Pr Inc, 480 pp, 2nd edition.

WHO (1997) Aluminium. Environmental Health Criteria 194.

Vangheluwe; M., Vercaigne,, Vandenbroele, M., Shtiza, A., Heijerick, D. (2010) White Paper on exposure based waiving for iron and aluminium in soil and sediments. Arche, Assessing Risks of Chemicals, 58 pp.