Aluminium tris(dihydrogen phosphate)

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Additional information

Aluminium tris(dihydrogen phosphate) is an inorganic substance and does not undergo biological degradation. The substance dissociates to dihydrogen phosphate and aluminium ions in aqueous and biological systems. Aluminium and phosphorus are both natural elements that are present in all environmental compartments. Aluminium and phosphorus species are removed from the water column by hydrolytic transformation or chemical precipitates. Precipitates of aluminium and phosphorus will be further transformed in soil and sediment systems by mineralization.

The complex environmental chemistry of aluminium is addressed in several reports and public available sources to date (ATSDR (2008), Environment Agency (2007), Environment Canada and Health Canada (2000), RIZA (2002), WHO (2010)). All sources document that aluminium is the third most common element of the earth's crust and thus very abundant in the environment. It is naturally released to the environment from the weathering of rocks and volcanic activity. It also enters the environment from anthropogenic sources such as drinking water and wastewater treatment. The phosphate anions are ubiquitous in natural waters and essential micronutrient for many organisms.

Bioaccumulation and secondary poisoning are considered not significant for aluminium tris(dihydrogen phosphate). The available data demonstrates no biomagnification of aluminium across the trophic levels in aquatic and terrestrial food chains due to its insolubility under neutral conditions. The existing information suggests not only that aluminium does not biomagnify, but that it tends to exhibit biodilution at higher trophic levels in the food chain (Cronan and Schofield, 1979). Phosphorus is an essential element and well-regulated in all living organisms. Under the normal environmental conditions neither aluminium tris(dihydrogen phosphate) as a substance nor its dissociation species are considered to bioaccumulate. Exposure of soil dwelling organisms and plants to aluminium of geogenic and anthropogenic origin is expected to be high. However, it is known that the bioavailability of aluminium is low and that the excretion of aluminium is fast. Therefore, bioaccumulation of aluminium is rarely observed in nature (cited in WHO 1997). Thus the risk of terrestrial bioaccumulation of aluminium is expected to be low.

The air compartment is considered not relevant for aluminium tris(dihydrogen phosphate). Aluminium tris(dihydrogen phosphate) is an inorganic solid. According to its physico-chemical properties transport and partition of aluminium tris(dihydrogen phosphate) in the atmosphere is of low concern. Release into air from a high temperature emission of the production is easily run down by raining. The amount of aluminium present in air that is related to the substance being considered here would be negligible compared with the amount of aluminium coming from natural erosion of soil (Environment Canada Health Canada, 2000).

The relative mobility of aluminium species depends upon many factors, especially pH, alkalinity, temperature, dissolved organic carbon, dissolved inorganic carbon and anion concentration. At low pH (less than 5.5), aluminium is present as highly mobile Al3+. As pH increases above 5.5, aluminium-hydroxide complexes and organically complexed aluminium are formed and may combine with organic matter. Above pH 7, anionic aluminium hydroxide dominates. Kaplan (2005) published several Kd values based on measured Al concentration in groundwater and sediment and suggested Al Kd values for soil, grout, gravel, clay to be 3700 mL/g and 5000 mL/g for concrete, respectively. Furthermore, aluminium species play also an important role in the adsorption of other trace metal or anions in soils and sediments. Furthermore, colloidal aluminium species play also an important role in the adsorption of other trace metals and anions in soils and sediments.

The phosphate adsorption is affected by numerous factors, e.g. pH, type and concentration of electrolytes, clay content, A1 and Fe oxides, and organic matter content (Razaq, 1989). At pH values normally found in soils (4.5 - 6.2) H2PO4 - and HPO4 -2 are the dominant species in soil. These ions can be dissolved in soil water and also absorb onto the surface (or adsorb into) solid matter in the soil. Two types of inorganic reactions control the concentration of phosphate ions in solution; these are precipitation-dissolution and sorption-desorption processes. Precipitation-dissolution reactions involve the formation and dissolving of precipitates, being significantly pH dependent. Sorption-desorption reactions involve sorption and desorption of ions and molecules from the surfaces of mineral particles, such as Al/Fe oxides/hydroxides, clay minerals and carbonates (Packer, 1998). Basically, phosphate adsorption dominates in mineral soil with low pH. 

 

Reference:

ATSDR (Agency for Toxic Substances and Disease Registry) (2008). Toxicological Profile for Aluminum. Atlanta,: Department of Health and Human Services, Public Health Service.

Busman, Lowell Marion, "Behavior of polyphosphates in soils " (1984). Retrospective Theses and Dissertations. Paper 8979.

Canada. (2000). Canadian Environmental Protection Act: Persistence and Bioaccumulation Regulations, P.C. 2000-348, 23 March, 2000, SOR/2000-107, Canada Gazette. Part II, vol. 134, no. 7, p. 607−612. Available from: http://canadagazette.gc.ca/partII/2000/20000329/pdf/g2-13407.pdf

Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment

Cronan C.S. and Schofield C.L , 1979. Aluminium leaching response to acid precipitation: effect on high elevation watersheds in the Northeast. Science 204, 304-306

Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for the Community action in the field of water policy

Environment Agency (2007) Proposed EQS for Water Framework Directive Annex VIII, Substances: aluminium (inorganic monometric), Science Report: SC040038/SR1; SNIFER Report: WFD52 (i); ISBN: 978 -1 -84432 -651 -8, Feb 2007

Kaplan D.I. (2005) Recommended Distribution Coefficients, Kd Values, for Special Analysis Risk Calculations Related to Waste Disposal and Tank Closure on the Savannah River Site (U), Westinghouse Savannah River Company Savannah River Site,

Parker J.E., Robertson J., Wansbrough H. (1998) Chemical Processes in New Zealand, Bd 2. New Zealand Institute of Chemistry, 01.01.1998.

Razaq, Ibrahim Bakry Abdul (1989) Effect of pH and exchangeable metals on phosphate adsorption by soils. Retrospective Theses and Dissertations, Paper 9170.

RIZA (2002), Een ad-hoc Maximaal Toelaatbaar Risiconiveau (MTR) voor aluminium in oppervlaktewater, , 4L1574.A1/R0001/EVDP/Nijm, 26 april 2002

WHO (1997). Environmental Health Criteria 194. Aluminum. International Programme on Chemical Safety (IPCS). Geneva ISBN 92 4 157194 2.

WHO (2010), Aluminium in drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality. Geneva, World Health Organization (WHO/HSE/WSH/10.01/13)).